Intraamniotic thyroxine (T4) effect in high risk pregnancies

Intraamniotic thyroxine (T4) effect in high risk pregnancies. We reported previously the beneficial influence of intraamniotic T4 injection in accelerating human fetal lung maturity. 48 hr. after T4 (250 μg) intraamniotic injection mean cord serum T4 conc. in 15 premature newborns was 17.6 ± 1.9 μg/100 ml, while the T4 conc. in a matched group was 11.6 ± 0.9 μg/100 ml, and rose 12 hr. postpartum to 23.7 ± 2.4 μg/100 ml. No change in maternal T4 conc. was observed. Mean cord serum T4 conc. in 17 premature newborns delivered more than 3 days following T4 intraamniotic injection, however, were not significantly different than controls. These data suggest that a) T4 (250 μg) injected intraamniotically is absorbed by the human fetus, b) the hyperthyroxinemia is only transient, and c) does not block the postnatal T4 surge.