Collares FM, et al. - In a population-based prospective cohort study among 5726 mothers, researchers investigated the associations of maternal thyroid function in early pregnancy with maternal body mass index (BMI) and weight gain during pregnancy. For this investigation, maternal TSH and FT4 levels at 13.5 weeks of gestation were measured. They evaluated maternal weight before pregnancy and in each trimester. According to findings, maternal thyroid function associations with weight gain during early pregnancy were stronger than those with weight gain in mid and late pregnancy. Maternal hypothyroidism was correlated with higher prepregnancy BMI and early pregnancy weight gain, whereas in maternal hyperthyroidism opposite effects were observed. Overall, they concluded that higher maternal TSH and lower FT4 levels in early pregnancy were related to higher prepregnancy BMI and higher gestational weight gains.