Women with Subclinical Hypothyroidism Are at Low Risk of Poor Pregnancy Outcome in Japan

Maternal subclinical hypothyroidism may be associated with adverse pregnancy outcomes, although not consistently across regions. Here, we sought to determine the effect of elevated thyroid-stimulating hormone (TSH) on pregnancy outcomes in Japanese women without known medical complications. TSH was determined by dried blood spots at 8-20 weeks of gestation, and 3.0-10.0 pU/mL of TSH was considered as elevated TSH (eTSH). A retrospective study involving 167 cases of eTSH was conducted. Five hundred and seventy eight of controls with normal TSH and without thyroid antibodies were selected. We compared a composite adverse maternal outcome comprised of spontaneous abortion, premature delivery, gestational diabetes mellitus (GDM), placental abruption, and pregnancy-induced hypertension, as well as composite adverse neonatal outcome including stillbirths, heavy for date, light for date, and a low Apgar score (< 7) at 5 minutes between two groups. The incidence of GDM was significantly higher in eTSH (p < 0.01); however, composite adverse maternal and neonatal outcome did not differ between groups (p = 0.19 and p = 0.50, respectively). Although 27 out of 167 cases in eTSH have antibodies, composite adverse outcome did not differ between eTSH with antibodies and controls (p = 0.64 and p = 0.50, respectively). Additionally, composite adverse maternal and neonatal outcome did not differ between the group larger than the median of TSH in eTSH (n = 81) and controls (p = 0.43 and p = 0.98, respectively). Thus, elevated TSH is not associated with overall adverse pregnancy outcomes in women without known medical complications.