Maternal thyroid function in multifetal pregnancies before and after fetal reduction

The aim of the study was to investigate maternal thyroid function in pregnancy by monitoring the circulating concentrations of thyroid stimulating hormone (TSH), free thyroxine (fT 4 ) and human chorionic gonadotrophin (hCG) in multifetal pregnancies before and after embryo reduction. We studied two groups of women: group 1 comprised singleton (n=12) and twin (n=12) pregnancies achieved after superovulation and in vitro fertilisation and embryo transfer (IVF-ET), and group 2 were multifetal pregnancies (n=39) undergoing selective fetal reduction to twin pregnancies. Blood samples were obtained initially at 10–12 weeks gestation (before fetal reduction) and then 4 and 8 weeks afterwards. Before fetal reduction, the circulating concentrations of fT4 in multifetal pregnancies were significantly greater than those in singleton or twin pregnancies (singleton, mean 16·49 pmol/l (interquartile range14·09–18·13 pmol/l); twins, 15·84 (15·36–