[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Embryology](https://durgical.com/en/embryology/) › [Fetal period, placenta and twins](https://durgical.com/en/embryology/#a-fetal) › Fetal growth and growth restriction

[Embryology](https://durgical.com/en/embryology/) · [Fetal period, placenta and twins](https://durgical.com/en/embryology/#a-fetal)

# Fetal growth and growth restriction

- Topic

The fetus grows on what the placenta delivers and on the insulin it makes itself. If the placenta fails, growth slows.

Updated 2026-11-01

## Key points

- Fetal insulin is the main growth hormone in the uterus; growth hormone matters little before birth.
- Glucose crosses the placenta, maternal insulin does not: maternal hyperglycaemia causes fetal hyperinsulinaemia and macrosomia.
- Symmetric restriction: early, with an intrinsic cause (aneuploidy, congenital infection).
- Asymmetric restriction: late, from placental insufficiency; the brain is spared and the abdomen stays small.
- Low birth weight: under 2500 grams, whether from prematurity or restriction.
- The infant of a diabetic mother risks neonatal hypoglycaemia from hyperinsulinism.

## What it is

Fetal growth depends on placental delivery of oxygen and glucose, on the fetus's own insulin and insulin-like growth factors, and on its genes. Fetal growth restriction is a fetus that does not reach its potential, nearly always because of placental insufficiency. At the other extreme, maternal hyperglycaemia causes fetal hyperinsulinaemia and macrosomia.

## Key facts

- First trimester: growth by more cells; third trimester: by larger cells and fat deposition.
- First-trimester crown–rump length is the best measure for dating a pregnancy.
- Small for gestational age (below the 10th centile) is not always restriction: some fetuses are constitutionally small.
- Altitude lowers birth weight; in high cities such as Bogotá newborns weigh less on average than at sea level.

## Symmetric and asymmetric restriction

| Feature | Symmetric | Asymmetric |
| --- | --- | --- |
| Onset | Early | Third trimester |
| [Typical cause](https://durgical.com/en/conditions/congenital-infections-syphilis-toxoplasmosis-cmv-and-zika/) | Aneuploidy, congenital infection | Placental insufficiency, preeclampsia |
| [Proportions](https://durgical.com/en/conditions/preeclampsia/) | Small head and body | Head spared, small abdomen |
| Outlook | Depends on the cause | Improves if supply is restored |

## Clinical notes

- Risk factors: hypertension and preeclampsia, smoking, alcohol, undernutrition, congenital infections, multiple pregnancy.
- Restriction raises the risk of stillbirth, asphyxia, neonatal hypoglycaemia and hypothermia.
- In Colombia the Instituto Nacional de Salud monitors low birth weight at term as a public health event.

## In the lab

- Fundal height smaller than expected: the first clinical sign.
- Ultrasound: estimated fetal weight or abdominal circumference below the 10th centile.
- Umbilical artery Doppler: absent or reversed end-diastolic flow signals severe placental insufficiency; middle cerebral artery dilation signals «brain sparing».

## Memory aid

When the placenta rations, the fetus protects the brain first: the head keeps growing and the belly falls behind.

## Test yourself

Think of the answer, then tap the question to see it.

## What is the main hormone driving fetal growth?

Fetal insulin, together with insulin-like growth factors; growth hormone plays little part before birth.

## Why does poorly controlled maternal diabetes cause macrosomic fetuses?

Because maternal glucose crosses the placenta and the fetal pancreas responds with hyperinsulinaemia, which drives growth and fat deposition.

## Which pattern of restriction does third-trimester placental insufficiency cause?

Asymmetric restriction: flow is redirected to the brain, the head is spared and the abdomen, with a small liver, lags behind.

## Which Doppler finding signals severe placental insufficiency?

Absent or reversed end-diastolic flow in the umbilical artery.

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## Related

- [Placenta: structure, circulation and functions](https://durgical.com/en/embryology/placenta-structure-circulation-and-functions/)
- [Fetal period: month 3 to birth](https://durgical.com/en/embryology/fetal-period-month-3-to-birth/)
- [Twins: dizygotic and monozygotic, chorionicity, twin–twin transfusion](https://durgical.com/en/embryology/twins-dizygotic-and-monozygotic-chorionicity-twin-twin-transfusion/)
- [Maternal diabetes and obesity as teratogens](https://durgical.com/en/embryology/maternal-diabetes-and-obesity-as-teratogens/)
- [TORCH infections: what each agent does to the embryo and fetus](https://durgical.com/en/embryology/torch-infections-what-each-agent-does-to-the-embryo-and-fetus/)
- [Ionizing radiation, tobacco and cocaine](https://durgical.com/en/embryology/ionizing-radiation-tobacco-and-cocaine/)
- [Gestational age vs fertilization age: how pregnancy is dated](https://durgical.com/en/embryology/gestational-age-vs-fertilization-age-how-pregnancy-is-dated/)

## Related conditions

- [Gestational diabetes mellitus](https://durgical.com/en/conditions/gestational-diabetes-mellitus/)
- [Preeclampsia](https://durgical.com/en/conditions/preeclampsia/)
- [Neonatal hypoglycaemia (including infant of a diabetic mother)](https://durgical.com/en/conditions/neonatal-hypoglycaemia/)
- [Congenital (TORCH) infections: syphilis, toxoplasmosis, CMV and Zika](https://durgical.com/en/conditions/congenital-infections-syphilis-toxoplasmosis-cmv-and-zika/)

[← All of embryology](https://durgical.com/en/embryology/)

Educational content on embryonic development; not a guide to prenatal diagnosis or to medicines in pregnancy and no substitute for a health professional's advice. No doses are given.

Sources: [Intrauterine growth restriction: MedlinePlus Medical Encyclopedia](https://medlineplus.gov/ency/article/001500.htm) (MedlinePlus, U.S. National Library of Medicine, 2024); [Placental insufficiency: MedlinePlus Medical Encyclopedia](https://medlineplus.gov/ency/article/001485.htm) (MedlinePlus, U.S. National Library of Medicine, 2024); Langman's Medical Embryology, 13th ed., ch. 8: Third Month to Birth: The Fetus and Placenta (Wolters Kluwer, 2015).

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Representative model, for educational purposes only.

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License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/embryology/fetal-growth-and-growth-restriction/