Plasma Thyrotrophin Levels During Pregnancy

Summary Plasma levels of thyrotrophin (TSH) were studied by radio‐immunoassay using homologous human TSH in 142 normal pregnant women and in 19 women with pre‐eclampsia, in 2 normal pregnant women who were followed up for almost a month, in 1 patient with a hydatidiform mole before and after hysterotomy, in 10 women 30 minutes after delivery and in the arterial and venous cord blood of 11 newborn infants. Thirty‐one normal euthyroid adults and 23 normal children were studied as controls. An increase in TSH plasma levels was found from the 7th week of pregnancy until delivery. Thirty minutes after delivery, and in the molar pregnancy 15 minutes after hysterotomy, the TSH levels returned to the upper normal range. In pre‐eclampsia the TSH plasma levels were found to be higher than in normal pregnancy. In the newborn at delivery the hypophyseal thyrotrophic function appeared to be slightly higher than in normal children. The increased plasma TSH level during pregnancy is probably due to the placental thyrotrophic‐like peptide secretion. During the different stages of purification from the placenta of human chorionic somatomammotrophin, immunoreacting thyrotrophic factor was found only in the starting material. The existence of a cross‐reaction between human TSH and human chorionic thyrotrophin was confirmed.