Zhang C, Yang X, Zhang Y, et al. - In this large prospective cohort study of a Chinese population, researchers intended to determine if there is a connection of maternal thyroid function during early and late pregnancy with birth weight. Between January 2013 and December 2016, pregnant women who had first-trimester prenatal screenings at the International Peace Maternity and Child Health Hospital were included. The sample consisted of 46,186 mothers in whom TSH, free thyroxine (FT4), T3, and thyroid peroxidase antibody concentrations were measured in the first and third trimesters and in whom data on birth weight were available. According to results, higher birth weight and increased risk of LGA were related to persistently low FT4 concentrations throughout pregnancy. Maternal TSH and FT4 correlations with birth weight varied by fetal gender. The monitoring of mildly altered thyroid hormone concentrations throughout pregnancy is recommended.