The findings of a cohort study by Professor Cnattingius et al. on maternal weight gain prior to the birth of a second child and the increased risk of stillbirth and infant mortality in the first year of life were recently published in THE LANCET and interviewed by Medscape. In 15% of women, the increase in body mass index (BMI) between the two births was between 2 and 4 (weight gain of 6-11 kg), and in 6% of women, the increase in BMI was greater than 4. This increase in weight, without counting the weight gain of the first birth, resulted in a 30% to 50% increase in the risk of stillbirth. For normal weight women, the same weight gain leads to a 27% to 60% increase in the risk of infant mortality in the first trimester. In contrast, for overweight women, studies have found that a reduction in BMI by 2 (6 kg) reduces the risk of infant mortality by 50%. Overweight and obesity are becoming a worldwide problem because of the association with pregnancy complications and may have a predictive effect on neonatal mortality. Weight gain between pregnancies has been associated with preeclampsia, gestational diabetes, preterm delivery and stillbirth. This association is more pronounced in normal weight women than in overweight or obese women. Professors Cnattingius and Villamor therefore investigated the effect of maternal weight gain between pregnancies on stillbirth and neonatal mortality in the second trimester. The researchers conducted a cohort study of birth registration data from the Swedish Medical Center between 1992 and 2012, including 456711 women who delivered their first and second child during this period, and assessed the effect of increased maternal BMI at first and second births on stillbirth (28 weeks and beyond) and infant mortality (up to 1 year). Of these participants, 13.1% had a BMI decrease ≤ 1 between births, 45.9% had no change in weight (BMI change of -1 to < 1), and 41.1% had a BMI increase ≥ 1. Women with a BMI increase > 4 had a 1.55 times greater risk of stillbirth and neonatal death compared to women with no significant change in weight between births. The risk of stillbirth increases linearly with BMI, with women with a BMI increase >4 having a 50% increased risk of stillbirth compared to women whose weight remained constant. With a normal first birth weight (<25 kg/O), weight gain between births increases second birth infant mortality, with a high infant mortality rate for BMI increases of 2 to 4 or 4. Although weight gain leads to a linear increase in infant mortality, it is only at a BMI gain ≥ 4 that mortality increases in young children after 1 year of age. Notably, for women who were overweight at their first birth, weight gain between births did not have an effect on infant mortality. In addition, for overweight women (BMI >25 kg/O), a reduction in maternal BMI of more than 2 significantly reduced infant mortality, but for women of normal weight, the same weight loss increased the risk of infant mortality. In these cohort studies, there was sufficient evidence of an association between weight gain and stillbirth between the two births, both in normal weight women and in overweight women. The studies also found that weight gain between pregnancies also increased the risk of subsequent stillbirths. The studies suggest that normal weight women should control their weight gain before pregnancy and that overweight women should lose weight.