View source for Birth weight

{{short description|Weight of a human neonate at birth}}
{{use dmy dates |date=March 2020 }}
[[File:Baby being weighed.jpg|thumb|Neonate weighed as appropriate for gestational age]]
'''Birth weight''' is the [[body weight]] of a [[neonate]] at their [[childbirth|birth]].<ref>{{cite web | url = http://oasis.state.ga.us/oasis/help/mch.html | title = Definitions | archive-url = https://web.archive.org/web/20120402214755/http://oasis.state.ga.us/oasis/help/mch.html | archive-date=April 2, 2012 | work = Georgia Department of Public Health | date = 4 December 2008 | quote = Birthweight: Infant's weight recorded at the time of birth }}</ref> The average birth weight in babies of European and African descent is {{Convert|3.5|kg|lb}}, with the normative range between {{Convert|2.5|and|4.0|kg|lb}}.<ref>{{Cite web |title=Birth Weight and Subsequent Risk of Type 2 Diabetes: A Meta-Analysis |url=https://academic.oup.com/aje/article/165/8/849/184757?login=true |access-date=2023-01-27 |website=academic.oup.com}}</ref> 

15% of babies born in 2012 had a low birth weight and 14.7% in 2020. It is projected that 14.2% of newborns will have low birth weight in 2030, falling short of the 2030 Sustainable Development Goals target of a reduction of 30%.<ref name=":32">{{Cite book |last1=FAO |url=https://openknowledge.fao.org/handle/20.500.14283/cd1254en |title=The State of Food Security and Nutrition in the World 2024 |last2=IFAD |last3=UNICEF |last4=WFP |last5=WHO |date=2024 |publisher=FAO ; IFAD ; UNICEF ; WFP ; WHO |isbn=978-92-5-138882-2 |language=English |doi=10.4060/cd1254en}}</ref>

On average, babies of Asian descent weigh about {{Convert|3.25|kg|lb}}.<ref>{{Cite web|url=https://www.thestar.com/life/parent/2012/02/15/new_birth_weight_curves_tailored_to_babys_ethnicity.html|title=New birth weight curves tailored to neonate's ethnicity {{!}} Toronto Star|website=thestar.com|date=15 February 2012|access-date=2016-09-22}}</ref><ref>{{cite journal | vauthors = Janssen PA, Thiessen P, Klein MC, Whitfield MF, Macnab YC, Cullis-Kuhl SC | title = Standards for the measurement of birth weight, length and head circumference at term in neonates of European, Chinese and South Asian ancestry | journal = Open Medicine | volume = 1 | issue = 2 | pages = e74–e88 | date = July 2007 | pmid = 20101298 | pmc = 2802014 }}</ref> The prevalence of low birth weight has changed over time. Trends show a slight decrease from 7.9% (1970) to 6.8% (1980), then a slight increase to 8.3% (2006), to the current levels of 8.2% (2016).<ref name=":0">{{cite web | work = Child Trends Databank | date = 2016 | title = Low and very low birthweight infants | url = https://www.childtrends.org/?indicators=low-and-very-low-birthweight-infants }}</ref><ref>{{Cite web|url=https://www.cdc.gov/nchs/fastats/birthweight.htm|title=FastStats|date=2018-08-08|website=www.cdc.gov|language=en-us|access-date=2018-11-25}}</ref> The prevalence of [[low birth weight]]s has trended slightly upward from 2012 to the present.<ref name="NVSS">{{cite journal | vauthors = Martin JA, Hamilton BE, Osterman MJ, Driscoll AK, Drake P | title = Births: Final Data for 2016 | journal = National Vital Statistics Reports | volume = 67 | issue = 1 | pages = 1–55 | date = January 2018 | pmid = 29775434 }}</ref>

Low birth weight is associated with [[neonatal infection]], [[infant mortality]], as well as illness into adulthood.<ref>{{Cite web |title=Australia's mothers and babies, Birthweight |url=https://www.aihw.gov.au/reports/mothers-babies/australias-mothers-babies/contents/baby-outcomes/birthweight |access-date=2023-01-27 |website=Australian Institute of Health and Welfare |language=en-AU}}</ref> Numerous studies have attempted, with varying degrees of success, to show links between birth weight and later-life conditions, including [[Diabetes mellitus|diabetes]], [[obesity]], [[tobacco smoking]], and [[intelligence]].<ref name=":6">{{cite journal | vauthors = Zhao Y, Wang SF, Mu M, Sheng J | title = Birth weight and overweight/obesity in adults: a meta-analysis | journal = European Journal of Pediatrics | volume = 171 | issue = 12 | pages = 1737–1746 | date = December 2012 | pmid = 22383072 | doi = 10.1007/s00431-012-1701-0 | s2cid = 25950922 }}</ref>

==Abnormalities==
*A [[low birth weight]] can be caused either by a [[preterm birth]] (low gestational age at birth) or the infant being [[small for gestational age]] (slow prenatal growth rate), or a combination of both.<ref name=":1">{{Cite news|url=https://www.marchofdimes.org/complications/low-birthweight.aspx|title=Low birthweight|access-date=2018-11-25|language=en-US}}</ref> Small for gestational age is defined as below the 10th percentile for gestational age and sex.<ref>{{Cite web |title=Australia's mothers and babies, Birthweight adjusted for gestational age |url=https://www.aihw.gov.au/reports/mothers-babies/australias-mothers-babies/contents/baby-outcomes/birthweight-adjusted-for-gestational-age |access-date=2023-01-27 |website=Australian Institute of Health and Welfare |language=en-AU}}</ref> Low birth weight can also be caused by health issues in the person giving birth, genetic factors, or problems in the [[placenta]].<ref>{{Cite web|title=Birth Weight|url=https://medlineplus.gov/birthweight.html|access-date=2020-10-29|website=medlineplus.gov}}</ref>
*A very large birth weight is usually caused by the infant having been [[large for gestational age]]. Large birth weight can be caused by maternal health issues such as gestational diabetes and obesity.<ref>{{cite journal | vauthors = Ye W, Luo C, Huang J, Li C, Liu Z, Liu F | title = Gestational diabetes mellitus and adverse pregnancy outcomes: systematic review and meta-analysis | journal = BMJ | volume = 377 | pages = e067946 | date = May 2022 | pmid = 35613728 | pmc = 9131781 | doi = 10.1136/bmj-2021-067946 }}</ref><ref>{{cite journal | vauthors = Marchi J, Berg M, Dencker A, Olander EK, Begley C | title = Risks associated with obesity in pregnancy, for the mother and baby: a systematic review of reviews | journal = Obesity Reviews | volume = 16 | issue = 8 | pages = 621–638 | date = August 2015 | pmid = 26016557 | doi = 10.1111/obr.12288 | s2cid = 206228471 | url = https://openaccess.city.ac.uk/id/eprint/12304/1/Risks%20associated%20with%20obesity%20in%20pregnancy%20%28final%20accepted%20version%29.pdf }}</ref> Large birth weight has been associated with significantly higher rates of neonatal morbidity.<ref>{{cite journal | vauthors = Mendez-Figueroa H, Truong VT, Pedroza C, Chauhan SP | title = Large for Gestational Age Infants and Adverse Outcomes among Uncomplicated Pregnancies at Term | journal = American Journal of Perinatology | volume = 34 | issue = 7 | pages = 655–662 | date = June 2017 | pmid = 27926975 | doi = 10.1055/s-0036-1597325 | s2cid = 4165673 }}</ref>

==Determinants==
[[File:Weight vs gestational Age.jpg|thumb|Relation of weight and [[Gestational age (obstetrics)|gestational age]]]]

=== Genetics ===
There are two genetic loci that have been strongly linked to birth weight, ''[[ADCY5]]'' and ''[[CCNL1]]'', and four that show some evidence (''[[CDKAL1]]'', ''[[HHEX]]–[[Insulin-degrading enzyme|IDE]]'', ''[[GCK (gene)|GCK]]'', and ''[[TCF7L2]]'').<ref>{{cite journal | vauthors = Freathy RM, Mook-Kanamori DO, Sovio U, Prokopenko I, Timpson NJ, Berry DJ, Warrington NM, Widen E, Hottenga JJ, Kaakinen M, Lange LA, Bradfield JP, Kerkhof M, Marsh JA, Mägi R, Chen CM, Lyon HN, Kirin M, Adair LS, Aulchenko YS, Bennett AJ, Borja JB, Bouatia-Naji N, Charoen P, Coin LJ, Cousminer DL, de Geus EJ, Deloukas P, Elliott P, Evans DM, Froguel P, Glaser B, Groves CJ, Hartikainen AL, Hassanali N, Hirschhorn JN, Hofman A, Holly JM, Hyppönen E, Kanoni S, Knight BA, Laitinen J, Lindgren CM, McArdle WL, O'Reilly PF, Pennell CE, Postma DS, Pouta A, Ramasamy A, Rayner NW, Ring SM, Rivadeneira F, Shields BM, Strachan DP, Surakka I, Taanila A, Tiesler C, Uitterlinden AG, van Duijn CM, Wijga AH, Willemsen G, Zhang H, Zhao J, Wilson JF, Steegers EA, Hattersley AT, Eriksson JG, Peltonen L, Mohlke KL, Grant SF, Hakonarson H, Koppelman GH, Dedoussis GV, Heinrich J, Gillman MW, Palmer LJ, Frayling TM, Boomsma DI, Davey Smith G, Power C, Jaddoe VW, Jarvelin MR, McCarthy MI | display-authors = 6 | title = Variants in ADCY5 and near CCNL1 are associated with fetal growth and birth weight | language = En | journal = Nature Genetics | volume = 42 | issue = 5 | pages = 430–435 | date = May 2010 | pmid = 20372150 | pmc = 2862164 | doi = 10.1038/ng.567 }}</ref><ref name=":3">{{cite journal | vauthors = Yaghootkar H, Freathy RM | title = Genetic origins of low birth weight | journal = Current Opinion in Clinical Nutrition and Metabolic Care | volume = 15 | issue = 3 | pages = 258–264 | date = May 2012 | pmid = 22406741 | doi = 10.1097/mco.0b013e328351f543 | s2cid = 3402464 }}</ref><ref>{{cite journal | vauthors = Ryckman KK, Feenstra B, Shaffer JR, Bream EN, Geller F, Feingold E, Weeks DE, Gadow E, Cosentino V, Saleme C, Simhan HN, Merrill D, Fong CT, Busch T, Berends SK, Comas B, Camelo JL, Boyd H, Laurie CC, Crosslin D, Zhang Q, Doheny KF, Pugh E, Melbye M, Marazita ML, Dagle JM, Murray JC | display-authors = 6 | title = Replication of a genome-wide association study of birth weight in preterm neonates | journal = The Journal of Pediatrics | volume = 160 | issue = 1 | pages = 19–24.e4 | date = January 2012 | pmid = 21885063 | pmc = 3237813 | doi = 10.1016/j.jpeds.2011.07.038 | author6-link = Eleanor Feingold }}</ref>  The [[heritability]] of birth weight ranges from 25 to 40%.<ref>{{cite journal | vauthors = Clausson B, Lichtenstein P, Cnattingius S | title = Genetic influence on birthweight and gestational length determined by studies in offspring of twins | journal = BJOG | volume = 107 | issue = 3 | pages = 375–381 | date = March 2000 | pmid = 10740335 | doi = 10.1111/j.1471-0528.2000.tb13234.x | s2cid = 43470321 | doi-access = }}</ref><ref>{{cite journal | vauthors = Lunde A, Melve KK, Gjessing HK, Skjaerven R, Irgens LM | title = Genetic and environmental influences on birth weight, birth length, head circumference, and gestational age by use of population-based parent-offspring data | journal = American Journal of Epidemiology | volume = 165 | issue = 7 | pages = 734–741 | date = April 2007 | pmid = 17311798 | doi = 10.1093/aje/kwk107 | doi-access = free }}</ref> There is a complex relationship between a baby's genes and the maternal environment that the child is developing in.<ref>{{cite journal | vauthors = Kobayashi S, Sata F, Kishi R | title = Gene-environment interactions related to maternal exposure to environmental and lifestyle-related chemicals during pregnancy and the resulting adverse fetal growth: a review | journal = Environmental Health and Preventive Medicine | volume = 27 | pages = 24 | date = 2022 | pmid = 35675978 | pmc = 9251623 | doi = 10.1265/ehpm.21-00033 }}</ref> [[Foetal]] genes influence how the fetus grows in [[Uterus|utero]], and the maternal genes influence how the environment affects the growing fetus.<ref name=":3" />

===Maternal health===
The [[health]] of the mother during the pregnancy can affect birth weight.  A [[Pre-existing disease in pregnancy|pre-existing disease]] or acquired disease in pregnancy is sometimes associated with decreased birth weight. For example, [[celiac disease]] confers an [[odds ratio]] of low birth weight of approximately 1.8.<ref name="TersigniCastellani2014">{{cite journal | vauthors = Tersigni C, Castellani R, de Waure C, Fattorossi A, De Spirito M, Gasbarrini A, Scambia G, Di Simone N | display-authors = 6 | title = Celiac disease and reproductive disorders: meta-analysis of epidemiologic associations and potential pathogenic mechanisms | journal = Human Reproduction Update | volume = 20 | issue = 4 | pages = 582–593 | year = 2014 | pmid = 24619876 | doi = 10.1093/humupd/dmu007 | doi-access = free | hdl = 10807/56796 | hdl-access = free }}</ref> Certain medications (e.g. for high blood pressure or epilepsy) can put a mother at a higher risk for delivering a low birth weight baby.<ref name=":1" /> Women younger than 15 or older than 35 are at a higher risk to have a low-birth weight baby.<ref name=":1" /><ref name="hrsa">{{Cite web |url=https://mchb.hrsa.gov/chusa11/hstat/hsi/pages/201lbw.html |title=Low Birth Weight |website=Child Health USA 2011 |access-date=2018-11-25}}</ref> Multiple births, where a mother has more than one child at one time, can also be a determinant in birth weight as each baby is likely to be outside the AGA (appropriate for gestational age). Multiple births put children at a higher rate to have low birth weight (56.6%) compared to children born in a single birth (6.2%).<ref name=":0" /> Low birth weight can also vary by maternal age. In 2008 the rate of low birth weight was the highest in babies born to women younger than 15 years old (12.4%).<ref name="hrsa"/> Women aged 40–54 had a rate of low birth weight at 11.8 percent. The lowest rates of low birth weight happened among babies whose mothers were between the ages of 25–29 years (4.4%) and 30–34 years (7.6%).<ref name="hrsa"/>

=== Stress ===
[[Psychological stress|Stressful]] events have been demonstrated to produce significant effects on birth weight. Those mothers who have stressful events during [[pregnancy]], especially during the first and second trimester, are at higher risk to deliver low birth weight babies.<ref name="Hedegaard">{{cite journal | vauthors = Hedegaard M, Henriksen TB, Secher NJ, Hatch MC, Sabroe S | title = Do stressful life events affect duration of gestation and risk of preterm delivery? | journal = Epidemiology | volume = 7 | issue = 4 | pages = 339–345 | date = July 1996 | pmid = 8793357 | doi = 10.1097/00001648-199607000-00001 | s2cid = 25514196 | jstor = 3702049 | doi-access = free }}</ref><ref name="Zhu et al.">{{cite journal | vauthors = Zhu P, Tao F, Hao J, Sun Y, Jiang X | title = Prenatal life events stress: implications for preterm birth and infant birthweight | journal = American Journal of Obstetrics and Gynecology | volume = 203 | issue = 1 | pages = 34.e1–34.e8 | date = July 2010 | pmid = 20417475 | doi = 10.1016/j.ajog.2010.02.023 }}</ref> Researchers furthered this study and found that maternal stressful events that occur prior to conception have a negative impact on birth weight as well, and can result in a higher risk for preterm and lower birth weight babies.<ref name="Witt et al.">{{cite journal | vauthors = Witt WP, Cheng ER, Wisk LE, Litzelman K, Chatterjee D, Mandell K, Wakeel F | title = Maternal stressful life events prior to conception and the impact on infant birth weight in the United States | journal = American Journal of Public Health | volume = 104 | issue = Suppl 1 | pages = S81–S89 | date = February 2014 | pmid = 24354829 | pmc = 3975462 | doi = 10.2105/AJPH.2013.301544 }}</ref><ref name="Khashan et al.">{{cite journal | vauthors = Khashan AS, McNamee R, Abel KM, Mortensen PB, Kenny LC, Pedersen MG, Webb RT, Baker PN | display-authors = 6 | title = Rates of preterm birth following antenatal maternal exposure to severe life events: a population-based cohort study | journal = Human Reproduction | volume = 24 | issue = 2 | pages = 429–437 | date = February 2009 | pmid = 19054778 | doi = 10.1093/humrep/den418 | doi-access = free }}</ref><ref name="Class et al.">{{cite journal | vauthors = Class QA, Khashan AS, Lichtenstein P, Långström N, D'Onofrio BM | title = Maternal stress and infant mortality: the importance of the preconception period | journal = Psychological Science | volume = 24 | issue = 7 | pages = 1309–1316 | date = July 2013 | pmid = 23653129 | pmc = 3713176 | doi = 10.1177/0956797612468010 }}</ref> Women who experienced abuse (physical, sexual, or emotional) during pregnancy are also at increased risk of delivering a low birth weight baby.<ref name="Murphy">{{cite journal | vauthors = Murphy CC, Schei B, Myhr TL, Du Mont J | title = Abuse: a risk factor for low birth weight? A systematic review and meta-analysis | journal = CMAJ | volume = 164 | issue = 11 | pages = 1567–1572 | date = May 2001 | pmid = 11402794 | pmc = 81110 }}</ref> For example, in a study completed by Witt et al., those women who experienced a stressful event (i.e. death of close family member, infertility issues, separation from partner) prior to conception had 38% more of a chance to have a very low birth weight baby compared to those who had not experienced a stressful life event.<ref name="Witt et al." /> Additionally, mothers with diagnosed post-traumatic stress disorder are more likely to give birth to a low birth weight infant.<ref>{{cite journal | vauthors = Sanjuan PM, Fokas K, Tonigan JS, Henry MC, Christian K, Rodriguez A, Larsen J, Yonke N, Leeman L | display-authors = 6 | title = Prenatal maternal posttraumatic stress disorder as a risk factor for adverse birth weight and gestational age outcomes: A systematic review and meta-analysis | journal = Journal of Affective Disorders | volume = 295 | pages = 530–540 | date = December 2021 | pmid = 34509068 | doi = 10.1016/j.jad.2021.08.079 | s2cid = 237485994 | pmc = 10481878 }}</ref> The theory is that stress can impact a baby based on two different mechanisms: neuroendocrine pathway or immune/inflammatory pathway.<ref name="Wadwha2">{{cite journal | vauthors = Wadhwa PD, Culhane JF, Rauh V, Barve SS | title = Stress and preterm birth: neuroendocrine, immune/inflammatory, and vascular mechanisms | journal = Maternal and Child Health Journal | volume = 5 | issue = 2 | pages = 119–125 | date = June 2001 | pmid = 11573837 | doi = 10.1023/A:1011353216619 | s2cid = 13524067 }}</ref><ref name=":2">{{cite journal | vauthors = Wadhwa PD, Culhane JF, Rauh V, Barve SS, Hogan V, Sandman CA, Hobel CJ, Chicz-DeMet A, Dunkel-Schetter C, Garite TJ, Glynn L | display-authors = 6 | title = Stress, infection and preterm birth: a biobehavioural perspective | journal = Paediatric and Perinatal Epidemiology | volume = 15 | issue = Suppl 2 | pages = 17–29 | date = July 2001 | pmid = 11520397 | doi = 10.1046/j.1365-3016.2001.00005.x | doi-access = free }}</ref> Stress causes the body to produce stress hormones called [[glucocorticoid]]s that can suppress the immune system, as well as raises levels of [[Corticotropin-releasing hormone|placental corticotropin-releasing hormone]] (CRH) which can lead to [[Preterm birth|preterm]] labor.<ref>{{cite journal | vauthors = Rich-Edwards J, Krieger N, Majzoub J, Zierler S, Lieberman E, Gillman M | title = Maternal experiences of racism and violence as predictors of preterm birth: rationale and study design | journal = Paediatric and Perinatal Epidemiology | volume = 15 | issue = Suppl 2 | pages = 124–135 | date = July 2001 | pmid = 11520405 | doi = 10.1046/j.1365-3016.2001.00013.x | doi-access = free }}</ref><ref name=":2" /> These findings can pose evidence for future prevention efforts for low birth weight babies. One way to decrease rates of low birth weight and premature delivery is to focus on the health of women prior to conception through reproductive education, screening and counseling regarding mental health issues and stress, and access to primary care.<ref name="Cheng">{{cite journal | vauthors = Cheng TL, Kotelchuck M, Guyer B | title = Preconception women's health and pediatrics: an opportunity to address infant mortality and family health | journal = Academic Pediatrics | volume = 12 | issue = 5 | pages = 357–359 | date = 2012 | pmid = 22658953 | pmc = 4443477 | doi = 10.1016/j.acap.2012.04.006 }}</ref>

===Racial stress===
Non-Hispanic Blacks have the highest infant mortality rate in the United States (11.4 deaths per 1,000 live births compared to the national average of 5.9 deaths per 1,000 live births).<ref name="CDC Infant Mortality">{{cite web|url=https://www.cdc.gov/reproductivehealth/MaternalInfantHealth/InfantMortality.htm|title=Infant Mortality {{!}} Maternal and Infant Health {{!}} Reproductive Health {{!}} CDC|date=3 August 2018|website=www.cdc.gov|language=en-us}}</ref> Subsequently,  there has been growing research supporting the idea of [[racial discrimination]] as a risk factor for low birth weight. In one study by Collins et al., evidence suggested that African American mothers who experienced high levels of racial discrimination were at significantly higher risk of delivering a very low-birth weight baby compared to African American mothers who had not experienced racial discrimination.<ref name="Collins et al.">{{cite journal | vauthors = Collins JW, David RJ, Handler A, Wall S, Andes S | title = Very low birthweight in African American infants: the role of maternal exposure to interpersonal racial discrimination | journal = American Journal of Public Health | volume = 94 | issue = 12 | pages = 2132–2138 | date = December 2004 | pmid = 15569965 | pmc = 1448603 | doi = 10.2105/AJPH.94.12.2132 }}</ref>

===Environmental factors===
[[File:RICO tobacco litigation corrective statement, Whitehall, PA (cropped).jpg|thumb|A [[United States v. Philip Morris|court-ordered]] corrective statement: "Smoking also causes reduced fertility, low birth weight in newborns, and cancer of the cervix" (United States, 2024).]]

Environmental factors, including exposure of the mother to [[secondhand smoke]]<ref name="sg-report">{{cite web | url = https://www.ncbi.nlm.nih.gov/books/NBK44324/ | title = The Health Consequences of Involuntary Exposure to Tobacco Smoke: A Report of the Surgeon General | publisher = [[Surgeon General of the United States]] | date = 2006-06-27 | access-date = 2014-06-16 |pages=198–205 | pmid = 20669524 | author1 = Office on Smoking Health (US) }}</ref> can be a factor in determining the birth weight of child. In 2014, 13% of children exposed to smoke were born with low birth weight compared with 8% of those children born to nonsmokers.<ref name=":0" /> Children born to mothers who smoked or were exposed to secondhand smoke are more likely to develop health problems earlier in life such as [[Developmental disability|neurodevelopmental delays]].<ref>{{cite journal | vauthors = Lee BE, Hong YC, Park H, Ha M, Kim JH, Chang N, Roh YM, Kim BN, Kim Y, Oh SY, Kim YJ, Ha EH | display-authors = 6 | title = Secondhand smoke exposure during pregnancy and infantile neurodevelopment | journal = Environmental Research | volume = 111 | issue = 4 | pages = 539–544 | date = May 2011 | pmid = 21397902 | doi = 10.1016/j.envres.2011.02.014 | bibcode = 2011ER....111..539L }}</ref>

When mothers actively smoke during pregnancy, their child is at a higher risk of being born with a low birth weight.<ref>{{cite journal | vauthors = Pereira PP, Da Mata FA, Figueiredo AC, de Andrade KR, Pereira MG | title = Maternal Active Smoking During Pregnancy and Low Birth Weight in the Americas: A Systematic Review and Meta-analysis | journal = Nicotine & Tobacco Research | volume = 19 | issue = 5 | pages = 497–505 | date = May 2017 | pmid = 28403455 | doi = 10.1093/ntr/ntw228 | s2cid = 3803610 }}</ref> Unfortunately, smoking is sometimes used as a stress management tool by expecting mothers.<ref>{{cite journal | vauthors = Damron KR | title = Review of the Relationships Among Psychosocial Stress, Secondhand Smoke, and Perinatal Smoking | journal = Journal of Obstetric, Gynecologic, and Neonatal Nursing | volume = 46 | issue = 3 | pages = 325–333 | date = May 2017 | pmid = 28390924 | doi = 10.1016/j.jogn.2017.01.012 | s2cid = 4576511 }}</ref> There is some support for lower [[socioeconomic status]] of the parents being a determinant of low birth weight, but there is conflicting evidence, as socioeconomic status is tied to many other factors.<ref name=":5">{{cite journal | vauthors = Mahumud RA, Sultana M, Sarker AR | title = Distribution and Determinants of Low Birth Weight in Developing Countries | journal = Journal of Preventive Medicine and Public Health = Yebang Uihakhoe Chi | volume = 50 | issue = 1 | pages = 18–28 | date = January 2017 | pmid = 28173687 | pmc = 5327679 | doi = 10.3961/jpmph.16.087 }}</ref><ref>{{cite journal | vauthors = Parker JD, Schoendorf KC, Kiely JL | title = Associations between measures of socioeconomic status and low birth weight, small for gestational age, and premature delivery in the United States | journal = Annals of Epidemiology | volume = 4 | issue = 4 | pages = 271–278 | date = July 1994 | pmid = 7921316 | doi = 10.1016/1047-2797(94)90082-5 | author-link = Jennifer D. Parker }}</ref><ref>{{cite journal | vauthors = Martinson ML, Reichman NE | title = Socioeconomic Inequalities in Low Birth Weight in the United States, the United Kingdom, Canada, and Australia | journal = American Journal of Public Health | volume = 106 | issue = 4 | pages = 748–754 | date = April 2016 | pmid = 26794171 | pmc = 4986052 | doi = 10.2105/AJPH.2015.303007 }}</ref>

== Neonatal care ==
Most babies admitted to the [[Neonatal intensive care unit|NICU]] are born before 37 weeks of pregnancy or have low birth weight which is less than {{convert|5.5|lb}}.<ref name="stanford">{{Cite web|url=https://www.stanfordchildrens.org/en/topic/default?id=the-neonatal-intensive-care-unit-nicu-90-P02389|title=The Neonatal Intensive Care Unit|website=Stanford Children Health |language=en-GB|access-date=2018-11-15}}</ref> They could also have a medical condition that requires special care. In the United States nearly half a million babies are born preterm. Because of this, many of these babies also have low birth weights.<ref name="stanford"/> There are four levels of care in the neonatal care units: [[Intensive care unit|intensive care]], high dependency care, low dependency, and transitional care:<ref name="LiverpoolWhat">{{Cite web|url=https://www.liverpoolwomens.nhs.uk/our-services/neonatal-care/what-is-neonatal-care/|title=What is neonatal care?|website=Liverpool Women's NHS Foundation Trust |language=en-GB|access-date=2018-11-25}}</ref>

* Intensive care: For babies with serious problems. This includes babies born three months early and with extremely low birth weight.
* High dependency care: For babies with less serious problems, but who still may need to be looked after or babies that are recovering from a critical illness.
* Low dependency care: For babies that do not need continuous supervision.
* Transitional care: For babies that still need medical treatment, but are well enough to be called for at their mother's bedside.

==Influence on early life==
[[File:Weigh your child every week.jpg|thumb|1930 poster from the [[Soviet Union]] encouraging mothers to weigh their babies weekly]]
Children born with an abnormally low birth weight can have significant problems within the first few years of life. They may have trouble gaining weight, obtaining adequate nutrition, and developing a strong immune system. They also have higher risks for mortality, behavior problems, and mental deficiencies.<ref name=":5" /> Low birth weight babies are more likely to develop the following conditions compared to normal birth weight babies:<ref name=":1" />

* Breathing problems ([[infant respiratory distress syndrome]])
* Bleeding in the brain ([[intraventricular hemorrhage]])
* [[Patent ductus arteriosus]] (PDA)
* [[Necrotizing enterocolitis]]
* [[Retinopathy of prematurity]]
* [[Neonatal jaundice|Jaundice]]
* Infections

That said, the effects of low birth weight on a child's first few years of life are often intertwined with other maternal, environmental, and genetic factors and most effects of low birth weight are only slightly negatively significant on a child's life when these factors are controlled for.<ref name=":4">{{cite journal | vauthors = Datar A, Jacknowitz A | title = Birth weight effects on children's mental, motor, and physical development: evidence from twins data | journal = Maternal and Child Health Journal | volume = 13 | issue = 6 | pages = 780–794 | date = November 2009 | pmid = 19308711 | pmc = 2855622 | doi = 10.1007/s10995-009-0461-6 }}</ref> When these factors are taken into account, the only significant effect low birth weight has on a child's development is early physical growth and the likelihood of being underweight, compared to those with a normal birth rate.<ref name=":4" />
[[File:All Causes world map - DALY - WHO2004.svg|thumb|upright=1.25|Disability-adjusted life years out of 100,000 lost due to any cause in 2004:<ref>{{Cite web |url=https://www.who.int/healthinfo/global_burden_disease/estimates_country/en/index.html |title=WHO Disease and injury country estimates |year=2009 |work=World Health Organization |access-date=Nov 11, 2009}}</ref>{{Div col|small=yes|colwidth=10em}}
{{legend|#b3b3b3|no data}}
{{legend|#ffff65|less than 9,250}}
{{legend|#fff200|9,250–16,000}}
{{legend|#ffdc00|16,000–22,750}}
{{legend|#ffc600|22,750–29,500}}
{{legend|#ffb000|29,500–36,250}}
{{legend|#ff9a00|36,250–43,000}}
{{legend|#ff8400|43,000–49,750}}
{{legend|#ff6e00|49,750–56,500}}
{{legend|#ff5800|56,500–63,250}}
{{legend|#ff4200|63,250–70,000}}
{{legend|#ff2c00|70,000–80,000}}
{{legend|#cb0000|more than 80,000}}
{{div col end}}]]

==Influence on adult life==
Studies have investigated how a person's birth weight can influence their future life, including potential links with [[obesity]], [[diabetes]] and [[intelligence (trait)|intelligence]].<ref name=":6" />

A baby born small or large for gestational age (either of the two extremes) was previously thought to have an increased risk of developing [[obesity]],<ref name="title3 stages of childhood may predict obesity risk - Fitness - MSNBC.com">{{cite web |url=http://www.nbcnews.com/id/8088161 |archive-url=https://web.archive.org/web/20160305104110/http://www.nbcnews.com/id/8088161/ |url-status=dead |archive-date=5 March 2016 |title=3 stages of childhood may predict obesity risk - Fitness - NBC News |website=[[NBC News]] |access-date=2007-11-28 |date=3 June 2005 }}</ref><ref>{{cite journal | vauthors = Singhal A, Wells J, Cole TJ, Fewtrell M, Lucas A | title = Programming of lean body mass: a link between birth weight, obesity, and cardiovascular disease? | journal = The American Journal of Clinical Nutrition | volume = 77 | issue = 3 | pages = 726–730 | date = March 2003 | pmid = 12600868 | doi = 10.1093/ajcn/77.3.726 | doi-access = free }}</ref> but it was later found that both high birth weight and maternal BMI are associated with increased risk of developing obesity in childhood.<ref name=":6" /><ref>{{cite journal | vauthors = Wang J, Liu E, Wang Y, Qiao Y, Zhang T, Li B, Zhang Z, Li N, Hu G | display-authors = 6 | title = Association of early pregnancy body mass index and children's birth weight with risk of being overweight in childhood | journal = American Journal of Human Biology | volume = 30 | issue = 5 | pages = e23174 | date = September 2018 | pmid = 30207617 | pmc = 6193846 | doi = 10.1002/ajhb.23174 }}</ref>

[[growth hormone therapy|Growth hormone (GH) therapy]] at a certain dose induced catch-up of lean body mass (LBM). However, percentage body fat decreased in the GH-treated subjects. [[Bone density|Bone mineral density]] SDS measured by [[DEXA]] increased significantly in the GH-treated group compared to the untreated subjects, though there is much debate over whether or not SGA (small for gestational age) is significantly adverse to children to warrant inducing catch-up.<ref>{{cite journal |title=GH Treatment Effects on Body Composition in SGA |journal=Growth, Genetics & Hormones |volume=24 |issue=1 |date=May 2008 |url=http://gghjournal.com/volume24/1/ab13.cfm |archive-url=https://web.archive.org/web/20080622212229/http://www.gghjournal.com/volume24/1/ab13.cfm |url-status=dead |archive-date=22 June 2008 }}</ref>
Babies that have a low birth weight are thought to have an increased risk of developing type 2 [[diabetes]] in later life.<ref>{{cite news |url=http://news.bbc.co.uk/1/hi/health/4293509.stm |title= Low birth weight diabetes link |access-date=2007-11-28 |work=BBC News | date=2005-02-25}}</ref><ref>{{cite journal | vauthors = Gillman MW, Rifas-Shiman S, Berkey CS, Field AE, Colditz GA | title = Maternal gestational diabetes, birth weight, and adolescent obesity | journal = Pediatrics | volume = 111 | issue = 3 | pages = e221–e226 | date = March 2003 | pmid = 12612275 | doi = 10.1542/peds.111.3.e221 | doi-access = free }}</ref><ref>{{cite journal | vauthors = Rich-Edwards JW, Colditz GA, Stampfer MJ, Willett WC, Gillman MW, Hennekens CH, Speizer FE, Manson JE | display-authors = 6 | title = Birthweight and the risk for type 2 diabetes mellitus in adult women | journal = Annals of Internal Medicine | volume = 130 | issue = 4 Pt 1 | pages = 278–284 | date = February 1999 | pmid = 10068385 | doi = 10.7326/0003-4819-130-4_part_1-199902160-00005 | s2cid = 17291266 }}</ref><ref>{{cite journal | vauthors = Li Y, Ley SH, Tobias DK, Chiuve SE, VanderWeele TJ, Rich-Edwards JW, Curhan GC, Willett WC, Manson JE, Hu FB, Qi L | display-authors = 6 | title = Birth weight and later life adherence to unhealthy lifestyles in predicting type 2 diabetes: prospective cohort study | journal = BMJ | volume = 351 | pages = h3672 | date = July 2015 | pmid = 26199273 | pmc = 4510778 | doi = 10.1136/bmj.h3672 }}</ref><ref>{{Cite journal |last1=Martín‐Calvo |first1=Nerea |last2=Goni |first2=Leticia |last3=Tur |first3=Josep A. |last4=Martínez |first4=J. Alfredo |date=January 2022 |title=Low birth weight and small for gestational age are associated with complications of childhood and adolescence obesity: Systematic review and meta‐analysis |journal=Obesity Reviews |language=en |volume=23 |issue=S1 |pages=e13380 |doi=10.1111/obr.13380 |pmid=34786817 |issn=1467-7881|doi-access=free |hdl=20.500.13003/19673 |hdl-access=free }}</ref> Low birth weight is linked with increase rates of obesity, [[insulin resistance]], and type 2 diabetes and it is shown that children with the low birth weights have increased [[leptin]] levels after they catch up growth during childhood.<ref name="leptin">{{cite journal | vauthors = Jornayvaz FR, Vollenweider P, Bochud M, Mooser V, Waeber G, Marques-Vidal P | title = Low birth weight leads to obesity, diabetes and increased leptin levels in adults: the CoLaus study | journal = Cardiovascular Diabetology | volume = 15 | pages = 73 | date = May 2016 | pmid = 27141948 | pmc = 4855501 | doi = 10.1186/s12933-016-0389-2 | doi-access = free }}</ref> [[Adiponectin]] levels are positively related with birth weight and BMI in babies with an increase of risk of type 2 diabetes.<ref name="leptin"/> The leptin and adiponection mechanisms are still being studied when involving low birth weight.<ref name="leptin"/>

== Around the world ==
There is much variation regarding birth weight within continents, countries, and cities.  Even though over 20 million babies are born each year with low birth weight, it is hard to know the exact number, as more than half of babies born in the world are not weighed at birth.<ref>{{Cite news|url=https://data.unicef.org/topic/nutrition/low-birthweight/|title=Low birthweight - UNICEF DATA|work=UNICEF DATA|access-date=2018-11-25|language=en-US}}</ref> The baby's weight is an indicator of the mother and baby's health. In 2013, 22 million newborns had low birth weight, around 16 percent of all babies globally.<ref name="unicef">{{Cite web|url=https://data.unicef.org/topic/nutrition/low-birthweight/|title=Low BirthWeight |website=UNICEF DATA|language=en-GB|access-date=2018-11-25}}</ref> Data on low birth weight is adjusted to account for under reporting. South Asia has the highest rate of babies not weighed at birth with 66 percent, but also have the highest low birth weight, at 28 percent worldwide.<ref name="unicef"/> West and Central Africa and least developed countries are next, with 14 percent low birth weight worldwide.<ref name="unicef"/>

More than 96.5% of low birth weight babies are born in developing countries around the world.<ref name=":5" /> Because low birth weight babies can require more extensive care, it places a financial burden on communities.

== Prevention ==
The [[World Health Organization]] (WHO) recently announced an initiative to have a thirty percent reduction in low birth weight worldwide. This is a public health priority, as birth weight can have short- and long-term effects. WHO estimates that worldwide, 15–20% of all births each year are considered low birth weight, which is about 20 million births.<ref name="WHOnutrition">{{Cite web |url=https://www.who.int/nutrition/publications/globaltargets2025_policybrief_lbw/en/|archive-url=https://web.archive.org/web/20150218100000/http://www.who.int/nutrition/publications/globaltargets2025_policybrief_lbw/en/|url-status=dead|archive-date=18 February 2015|title=Global Nutrition Targets 2025: Low birth weight policy brief|website=World Health Organization|language=en-GB|access-date=2018-11-25}}</ref>

The start of prenatal care is very important to help prevent low birth weight and early medical problems. Going to regular doctor's visits is very important for the health of the mother and the baby. At the visits, OB/GYNs check maternal nutrition and weight gain because they are linked to the baby's weight gain. The mother having a healthy diet is essential for the baby. Maintaining good nutrition by taking [[folic acid]], which can be found in fruits and vegetables, is linked to the prevention of<ref>{{Cite web | url=https://www.sciencedaily.com/releases/2014/11/141125205859.htm |title = New study examines effect of timing of folic acid supplementation during pregnancy |website=ScienceDaily.com}}</ref><ref>{{cite journal | vauthors = Hodgetts VA, Morris RK, Francis A, Gardosi J, Ismail KM | title = Effectiveness of folic acid supplementation in pregnancy on reducing the risk of small-for-gestational age neonates: a population study, systematic review and meta-analysis | journal = BJOG | volume = 122 | issue = 4 | pages = 478–490 | date = March 2015 | pmid = 25424556 | doi = 10.1111/1471-0528.13202 | s2cid = 8243224 | doi-access = }}</ref> premature births and low birth weight.  Alcohol, cigarettes, and drugs should also be avoided during pregnancy because they can also lead to poor growth and other complications.<ref>{{cite journal | vauthors = Polańska K, Jurewicz J, Hanke W | title = Smoking and alcohol drinking during pregnancy as the risk factors for poor child neurodevelopment - A review of epidemiological studies | language = english | journal = International Journal of Occupational Medicine and Environmental Health | volume = 28 | issue = 3 | pages = 419–443 | date = 2015-05-18 | pmid = 26190723 | doi = 10.13075/ijomeh.1896.00424 | doi-access = free }}</ref> Doctors are also able to monitor pre-existing medical illnesses to make sure they are under control during pregnancy. Mothers with [[Hypertension|high blood pressure]] and [[Diabetes mellitus type 2|type 2 diabetes]] are more likely to have infants with low birth weights.<ref>{{Cite web|url= https://www.healthxchange.sg/women/pregnancy/low-birth-weight-babies-prevention|title=Low and Very Low Birth Weight Babies:Prevention Tips for Expectant Mothers|website=HealthXchange|language=en-gb|access-date=2018-11-16}}</ref> One essential action to increase normal birth weights is to have affordable, accessible, and [[culturally sensitive]] prenatal care worldwide. This is essential not just for treating low birth weight, but also preventing it.  Other prevention efforts include [[smoking cessation]] programs, food-distribution systems, stress reduction and social service supports.<ref name="WHOnutrition" />

== See also ==
*[[Infant mortality]]
*[[Low birth-weight paradox]]
*[[MOMO syndrome]]
*[[Prenatal nutrition]]
*[[Thrifty phenotype]]

== Sources ==
{{Free-content attribution
| title = The State of Food Security and Nutrition in the World 2024
| author = FAO, IFAD, UNICEF, WFP and WHO
| publisher = FAO
| documentURL = https://openknowledge.fao.org/handle/20.500.14283/cd1254en
| license = CC BY 4.0
}}

== References ==
{{reflist|30em}}

== Further reading ==
{{refbegin}}
* {{cite journal | vauthors = Peleg D, Kennedy CM, Hunter SK | title = Intrauterine growth restriction: identification and management | journal = American Family Physician | volume = 58 | issue = 2 | pages = 453–60, 466–7 | date = August 1998 | pmid = 9713399 | url = http://www.aafp.org/afp/980800ap/peleg.html | access-date = 5 June 2005 | archive-date = 6 June 2011 | archive-url = https://web.archive.org/web/20110606040232/http://www.aafp.org/afp/980800ap/peleg.html | url-status = dead }}
* {{cite journal | vauthors = Jornayvaz FR, Vollenweider P, Bochud M, Mooser V, Waeber G, Marques-Vidal P | title = Low birth weight leads to obesity, diabetes and increased leptin levels in adults: the CoLaus study | journal = Cardiovascular Diabetology | volume = 15 | pages = 73 | date = May 2016 | pmid = 27141948 | pmc = 4855501 | doi = 10.1186/s12933-016-0389-2 | doi-access = free }}
{{refend}}

== External links ==
* {{MedlinePlusEncyclopedia|001500|Intrauterine growth restriction}}
* {{eMedicine|med|3247|Fetal Growth Restriction}}

{{Pregnancy}}
{{Infants and their care}}
{{Authority control}}

{{DEFAULTSORT:Birth weight}}
[[Category:Obstetrics]]
[[Category:Neonatology]]
[[Category:Human body weight]]
[[Category:Midwifery]]