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 μ U/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.

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