You’re 35. Is your baby doomed?

The idea that a woman’s fertility declines during her thirties is based on some dubious statistics, writes Jessica Grose at Slate. Some of the oft-cited statistics on birth and conception rates come from eighteenth-century French surveys, or from “no specific published medical literature” at all.

Yet, there is a specific reason why 35 is considered a sharp cutoff for the condition of “advanced maternal age.” It’s nothing to do with fertility.

The test for Down syndrome, done during pregnancy, is risky. It involves sampling the amniotic fluid the baby floats in with a gigantic needle. There is about a 1 in 300 chance of miscarriage as a result of the test.


Fish en amniocitos

Chromosomes fluoresce in a fetal cell, in one type of amnocentesis testing. Credit: Instituto Bernabeu

The risk of Down syndrome rises with a mother’s age, from about one baby in every thousand at age 30 to ten at age 40. The rise is dramatic over that decade but smooth: there isn’t a jump at 35. Rather, 35 is the magic number because that’s when the risk of Down syndrome is equal to the risk of miscarrying from the test.

In the past, testing for Down syndrome and other chromosomal abnormalities was only offered to the 35-and-up crowd, but guidelines have changed and there are less-invasive, though less conclusive, tests available. The “advanced maternal age” moniker stuck, and is still considered useful … but nothing terrible happens at age 35.

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  1. harvey — December 5, 2013 @ 2:02 pm

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