Pregnancy changes how hundreds of genes work in a woman's body

It’s no secret that women’s bodies go through radical changes during pregnancy, but we’re finally starting to understand what happens at the gene level.

Alicia Smith at Emory University in the US and her colleagues took blood samples from 63 women early and late in pregnancy to see if they could detect any changes in their gene expression.

Of the 16,000 genes they looked at, they found that 439 altered their activity between the first and third trimester of pregnancy.

Many of these changes occurred in genes involved in the immune and circulatory systems, both of which are known to undergo major transformations during pregnancy.

Protect the fetus

For instance, the researchers observed increased expression of several genes from the alpha-defensin family, which help to fight disease-causing bacteria, fungi and viruses. This is probably to protect the fetus from microbes like listeria that can cause spontaneous abortion and pre-term birth, says Smith.

Changes were also seen in genes that protect the fetus from the mother’s own immune system. “Your immune system is designed to identify foreign cells and fight them, which makes carrying a fetus very complicated,” says Smith. “That’s why pregnancy is associated with a number of immune changes that stop your body from rejecting the foreign fetus.”

Another finding was that genes involved in oxygen transport in blood were upregulated during pregnancy. This is probably because women produce more blood when pregnant to deliver adequate oxygen to the fetus and safeguard against blood loss during delivery, says Smith.

Knowing how gene activity changes during normal, healthy pregnancies will hopefully allow us to develop tests that can pick up abnormal changes, says Smith. “We’re hoping this will be useful for predicting which women are at risk of pre-term birth and other pregnancy complications,” she says.