Maternal preconception diet and the sex ratio.

Temporal variations in the sex ratio, or the ratio of boys to girls at birth, have been widely studied and variously attributed to social changes, conditions of war, and environmental changes. Recently, Mathews et al. ["You are what your mother eats: Evidence for maternal preconception diet influencing fetal sex in humans," Proc. R. Soc. bond. B 275:1661-1668 (2008)] studied the direct evidence of individual pregnancies and established an association between the sex at birth and the mother's preconception diet. We examined the hypothesis using new evidence from the wartime famine in Holland in 1944-1945 and failed to show an association between maternal diet in pregnancy and the sex ratio. This makes a causal link highly improbable.