Sex Differences in birth size and intergenerational effects of intrauterine exposure to Ramadan in Saudi Arabia

Objectives: In Europe, boys and girls have different body proportions at birth. We examined newborn babies in Saudi Arabia to determine the sex differences and whether fetal growth differed if the mother was in utero during Ramadan. Methods: We examined body size at birth among 967 babies (479 boys and 488 girls) born in Unizah, a small city in Saudi Arabia. Results: Large head circumference was the strongest single predictor of male sex. In a simultaneous regression, female sex was predicted by small head circumference (P < 0.001), low birth weight (P = 0.002), and large chest circumference (P = 0.008). The mothers of boys were heavier in pregnancy than the mothers of girls and had a higher body mass index, 31.7 kg/m ² compared to 30.2 (P < 0.001). The mothers of girls, however, were taller than the mothers of boys, 158.6 cm compared to 157.4 (P = 0.001). Compared to babies whose mothers were not in utero during Ramadan boys whose mothers were in mid gestation during Ramadan were 1.2 cm longer (P = 0.005) while girls had a 0.4 week shorter gestation period (P = 0.04). Conclusion:: Our findings are consistent with other evidence that boys are more ready than girls to trade off visceral development in utero to protect somatic and brain growth. They also support the hypothesis that boys are more responsive to their mother's current diet than girls, who respond more to their mother's life time nutrition and metabolism. They provide the first evidence that changes in the life style of pregnant women during Ramadan affect more than one generation.