Birth-Weight

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

Newborn infant

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.

At birth, infants are generally weighed as soon as possible and may also be monitored during the neonatal period.

Links: Ultrasound | Fetal Origins Hypothesis | Maternal Diabetes | Macrosomia

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.

Human Birth Weight Classifications											no colour
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		Very Low Birth Weight	Low Birth Weight		Normal Birth Weight			High Birth Weight

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 * macrosomia

No Background Version

Human Birth Weight Classifications
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		Very Low Birth Weight	Low Birth Weight		Normal Birth Weight			High Birth Weight

Small for Gestational Age

Gastroschisis Birth Weight Graph

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.

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.

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. 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."

References

Articles

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Search Pubmed

Search Pubmed: Low Birth Weight | small for gestational age

External Links

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• CDC Pediatric Nutrition Surveillance System - Birthweight

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Cite this page: Hill, M.A. (2024, April 18) Embryology Birth-Weight. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Birth-Weight

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© Dr Mark Hill 2024, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G