The effects of gestational transient thyrotoxicosis on the perinatal outcomes: a case-control study

To study the effects of gestational transient thyrotoxicosis (GTT) on pregnancy outcomes.

This case-control study retrospectively analyzed 7976 women with singleton pregnancies whose thyroid function was measured before 16 weeks of gestation and who delivered at ≥22 weeks of pregnancy. GTT was defined as hyperthyroidism (free thyroxine [FT4] level: ≥95th percentile) in the early pregnancy, which normalized in mid-pregnancy without thyroid-stimulating hormone receptor antibodies. Using data extracted from electronic records, we examined the association between GTT and the pregnancy outcomes (preterm delivery, gestational age at delivery, pregnancy induced hypertension (PIH), preeclampsia, placental abruption, caesarian section, birth weight, low birth weight, Apgar score, cord pH, stillbirth at gestational week ≥22, and neonatal death). We classified the cases into quartiles according to their FT4 values during the early pregnancy and investigated the association with the gestational age at delivery.

Two hundred and eight cases of GTT and 6317 cases with normal thyroid assessments were reviewed. GTT was associated with hyperemesis gravidarum, but not with stillbirth, preterm delivery, PIH, preeclampsia, placental abruption, or low birth weight. The gestation period was shorter in patients with GTT than in those with a normal thyroid function (38.69 ± 1.79 vs. 39.07 ± 1.64 weeks, p < 0.01). Higher FT4 levels during the early pregnancy were associated with earlier delivery (p = 0.02).

GTT was associated with a lower gestational age at delivery but not with adverse pregnancy outcomes. There was a negative correlation between the FT4 values in the early pregnancy and the gestational period.