Genetic conflict with the fetus influences when women give birth
Longer-lasting pregnancies lead to larger babies but also riskier births, but some genes may have let women and fetuses find a middle ground
By Clare Wilson
3 April 2023
A longer pregnancy supports a fetus’ growth, but giving birth to a large baby comes with risks
Suttipong Surak/EyeEm/Getty Images
When it comes to the length of pregnancy, fetuses and those carrying them may have slightly different interests. Now, the largest study into how genes affect the timing of childbirth suggests that the two parties reached an evolutionary compromise.
Gene variants that, in women, promote a shorter pregnancy, also encourage faster fetal growth when present in fetuses. “They have reached some kind of a deal, with the mother saying: ‘I’m going to allow you to grow a little bit more, but I’m going to deliver a little bit earlier’,” says Pol Solé Navais at the University of Gothenburg, Sweden.
Premature birth – defined as delivery before 37 weeks of pregnancy – is one of the leading causes of death in newborns globally, but the causes are poorly understood.
Advertisement
To explore the genetic influences of pregnancy length, Solé Navais’s team pooled the results of previous studies that together included around 200,000 women who started giving birth at various stages of pregnancy without being medically induced. Transgender people weren’t included.
These studies sequenced the DNA of both the women and their babies, as well as noting aspects such as how long the pregnancies lasted and the babies’ birth weight.
Solé Navais’s team found 22 sites within the genome that each had a small influence on the timing of birth, of which five had opposite effects when present in the mother or the fetus. In other words, if a certain variant were present in the mother, it was linked with a shorter pregnancy, while if present in the fetus, it was associated with a longer pregnancy.
