Birth Weight
Embryology - 19 Jun 2024 Expand to Translate |
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Educational Use Only - Embryology is an educational resource for learning concepts in embryological development, no clinical information is provided and content should not be used for any other purpose. |
Introduction
There are a variety of prenatal techniques for estimating approximate birth weight that are relevant for preterm, term and prolonged pregnancy. Ultrasound two- and three-dimensional scanning methods are the basis of most current techniques. There are also standard autopsy weight curves that have been developed from second and third trimester fetal and also neonatal autopsy. Low birth weight is accurately defined as a statistical indicator for development. High birthweight definition on the other hand varies in the literature and between countries with a lower cut-off above 4000 gm or 4500 gm.
At birth, infants are generally weighed as soon as possible and may also be monitored during the neonatal period. In Australia, the average birthweight for all babies born in 1991 was 3,350 grams and about the same in 2004 at 3,370 grams.
- Links: Ultrasound | Fetal Origins Hypothesis | Maternal Diabetes | Macrosomia
Some Recent Findings
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More? References | Discussion Page | Journal Searches | 2019 References | 2020 References Search term: Birth Weight <pubmed limit=5>Birth Weight</pubmed> |
Birth Weight Classifications
The primary causes of VLBW are premature birth (born <37 weeks gestation, and often <30 weeks) and intrauterine growth restriction (IUGR), usually due to problems with placenta, maternal health, or to birth defects. Many VLBW babies with IUGR are preterm and thus are both physically small and physiologically immature.
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Birth weight (grams) | less 500 | 500 – 999 | 1,000 – 1,499 | 1,500 – 1,999 | 2,000 – 2,499 | 2,500 – 2,999 | 3,000 – 3,499 | 3,500 – 3,999 | 4,000 – 4,499 | 4,500 – 4,999 | 5,000 or more |
Classification |
Extremely Low Birth Weight
- Less than 500 grams (1 lb 1 oz or less)
- 500 – 999 grams (1 lb 2 oz – 2 lb 3 oz)
Very Low Birth Weight
- 1,000 – 1,499 grams (2 lb 4 oz – 3 lb 4 oz)
Low Birth Weight
- 1,500–1,999 grams (3 lb 5 oz – 4 lb 6 oz)
- 2,000–2,499 grams (4 lb 7 oz – 5 lb 8 oz)
Normal Birth Weight
- 2,500–2,999 grams (5 lb 9 oz – 6 lb 9 oz)
- 3,000–3,499 grams (6 lb 10 oz – 7 lb 11 oz)
- 3,500–3,999 grams (7 lb 12 oz – 8 lb 13 oz)
High Birth Weight
- 4,000–4,499 grams (8 lb 14 oz – 9 lb 14 oz)
- 4,500–4,999 grams (9 lb 15 oz – 11 lb 0 oz)
- 5,000 grams or more (11 lb 1 oz or more)
- see also Birth - Macrosomia
No Background Version
Birth weight (grams) | less 500 | 500 – 999 | 1,000 – 1,499 | 1,500 – 1,999 | 2,000 – 2,499 | 2,500 – 2,999 | 3,000 – 3,499 | 3,500 – 3,999 | 4,000 – 4,499 | 4,500 – 4,999 | 5,000 or more |
Classification |
Small for Gestational Age
(SGA) Term used for infants as having a birth weight more than 2 standard deviations (SD) below the mean or less than the 10th percentile for the gestational age ((GA}}. WHO birthweight definitions are low birthweight as less than 2,500 grams, very low birthweight is less than 1,500 grams and extremely low birthweight: less than 1,000 grams. Growth restriction can be symmetrical (slow development with limited brain growth) or asymmetrical (head circumference and length are preserved and brain growth is relatively spared).
- Symmetric SGA (Weight, head circumference and length all below the 10th percentile) can be due to chromosomal abnormalities, intrauterine infection, severe placental insufficiency and or a constitutionally small infant.
- Asymmetric SGA (Weight below the 10th percentile) can be due to interference with placental function and or interference with maternal health in 3rd trimester.
There are a large number of known relationships between low birth weight and both maternal and fatal abnormalities, a few examples are shown below.
Fetal Gastroschisis
Gastroschisis patients are commonly small for gestational age (SGA, birth weight < 10th centile). Frequency line graphs of the birth weight distribution.[5]
The abnormality is usually situated to the right of the umbilicus and abdominal contents, mainly gastrointestinal, are found outside the anterior body wall. Can occur in isolation and also in association with other gastrointestinal anomalies (intestinal atresia, perforation, necrosis or volvulus). Defects in other organ systems have been reported in up to 35% of children.
Maternal Elevated Testosterone
Maternal elevated testosterone levels is associated with low birth weight in humans. Hyperandrogenism associated with polycystic ovarian syndrome (PCOS) and pre-eclampsia have a higher prevalence of small-for-gestational age newborns. A rat model study suggests that maternal testosterone does not cross the placenta, to directly suppress fetal growth, but affects nutrient delivery to the fetus by down-regulating specific amino acid transporter activity.[6]
High Altitude
Altitude affects growth patterns measured in a a recent Peruvian study of 63,620 healthy infants born at low (150 m) and high (3000-4400 m) altitude were compared. [7] They found that in the third trimester "Mean and median birth weight differences between those born at low and high altitudes reached statistical significance after 35 and 33 weeks, respectively."
Canada
Definition: Live births with a birth weight of 4,500 grams or more, expressed as a percentage of all live births with known birth weight.
High birth weight can result in complications for the infant and mother during birth and may be associated with an increased risk of diabetes.
- Links: Statistics Canada, Vital Statistics, Birth Database.
Australia - Indigenous
Australian low birth weight (2008–2009)[8]
Data in graphs below from AIHW 2014 Report, Birthweight of babies born to Indigenous mothers.[1]
Birthweight distribution | Average Birthweight (2000-2011) |
Preterm Birth | Smoking in Pregnancy |
- Links: Australian Statistics | Preterm Birth | Smoking
References
- ↑ 1.0 1.1 AIHW 2014. Birthweight of babies born to Indigenous mothers. Cat. no. IHW 138. Canberra: AIHW. Viewed 5 August 2014 http://www.aihw.gov.au/publication-detail/?id=60129548202
- ↑ <pubmed>24908671</pubmed>
- ↑ <pubmed>24941024</pubmed>| PLoS One.
- ↑ <pubmed>23733791</pubmed>
- ↑ <pubmed>22004141</pubmed>| BMC Pediatr.
- ↑ <pubmed>21812961</pubmed>| Reprod Biol Endocrinol.
- ↑ <pubmed>19038011</pubmed>
- ↑ AIHW 2014. Health indicators for Remote Service Delivery communities: a summary report. Cat. no. IHW 142. Canberra: AIHW. Viewed 5 November 2014 http://www.aihw.gov.au/publication-detail/?id=60129548650.
Articles
<pubmed>19581044</pubmed>
Search Pubmed
Search Pubmed: Low Birth Weight | small for gestational age
External Links
External Links Notice - The dynamic nature of the internet may mean that some of these listed links may no longer function. If the link no longer works search the web with the link text or name. Links to any external commercial sites are provided for information purposes only and should never be considered an endorsement. UNSW Embryology is provided as an educational resource with no clinical information or commercial affiliation.
- METoER (Australia) Birth—birth weight, code N
- CDC (USA) Pediatric Nutrition Surveillance System - Birthweight
- WHO Low Birthweight (2004) PDF
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Cite this page: Hill, M.A. (2024, June 19) Embryology Birth Weight. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Birth_Weight
- © Dr Mark Hill 2024, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G