Thyroxine concentration and outcome of hyperemetic pregnancies.

Plasma total thyroxine (TT4) and free thyroxine (FT4) were measured in 23 women with hyperemesis gravidarum at presentation, on average at about 10 weeks, in the second trimester, and before delivery. The first TT4 was raised abnormally in eight women and the FT4 in nine, but by the second trimester the TT4 was abnormally high in only three although in eight the FT4 remained high. By the third trimester all measurements, except one slightly raised FT4, were normal. Birthweight was not related to the thyroxine levels but there was a weak significant negative correlation between FT4 in the second trimester and gestational age at delivery.