Which of the following hormones is often decreased by approximately 25% in the serum of pregnant women who have a fetus with Down syndrome?

The correct answer is estriol (E3), which is a hormone produced primarily during pregnancy. When a fetus has Down syndrome, studies have shown that the levels of estriol in the mother’s serum can be significantly decreased, with studies reporting reductions around 25%. This decrease is linked to the placental function and fetal development; the presence of the fetus with Down syndrome can affect the production and metabolism of this hormone, leading to lower levels in the maternal serum.

Estriol is measured in maternal serum as part of screening tests for fetal anomalies, including Down syndrome. The decline in estriol can serve as a biochemical marker indicating potential issues with fetal development, making it a critical component in the assessment of the risk of chromosomal abnormalities.

Other hormones listed, such as human chorionic gonadotropin (hCG), progesterone, and estradiol (E2), do not show the same pronounced decrease in cases of Down syndrome and are not used in the same way as estriol in the context of screening for this condition. Thus, estriol is distinct in its association with pregnancy complications and chromosomal abnormalities.