Embryology · Fetal period, placenta and twins

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

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	Aneuploidy, congenital infection	Placental insufficiency, preeclampsia
Proportions	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».

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.

Add to my cards (4)

← All of 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 (MedlinePlus, U.S. National Library of Medicine, 2024); Placental insufficiency: MedlinePlus Medical Encyclopedia (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).

Spotted a mistake?We are always improving for the community. Tell us what is wrong and our team will review it.Report a mistake

Representative model, for educational purposes only.