Human reproduction
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Previous studies suggest that stressful pregnancies may be associated with a lower proportion of male relative to female offspring. Low or high maternal age may represent stress for the fetus. Our aim was therefore to study whether the sex ratio differs by maternal age in all pregnancies, and in separate analyses, to assess the sex ratio in pregnancies complicated by pre-eclampsia, fetal death, preterm delivery or small for gestational age (SGA) offspring. ⋯ The lower proportion of male births at high maternal age in pregnancies with pre-eclampsia and in pregnancies with live born SGA offspring born at term, supports the hypothesis that male fetuses are more vulnerable to maternal stress than female fetuses. The main limitation of our findings is lack of statistical power due to small study subpopulations.