Decrease of free thyroxin in serum of lactating women

Abstract

We measured thyroid hormones and thyroxin-binding proteins in serum from 62 normal lactating and 52 nonlactating women at three months postpartum, and compared these values with those for 42 nonpregnant control women of similar age. Mean thyroxin concentrations in the lactating and nonlactating women were significantly (P <0.001) lower than that of the nonpregnant controls, but there was no significant difference (P >0.2) in triiodothyronine concentration among these three groups. Free T4 concentration was significantly (P <0.01) lower in lactating women than in controls. The reverse-T3 concentrations in both lactating and nonlactating women were significantly (P <0.001) lower than in controls and were significantly (P <0.001) lower in lactating than in nonlactating women. The concentration of thyroxin-binding globulin was significantly higher in lactating women than in controls, and the albumin concentration was significantly lower in women postpartum than in controls. Evidently, regulation of thyroid hormone in women postpartum, especially during lactation, differs from that in nonpregnant women.