In pregnant women, maternal thyrotropin (TSH) levels >4 mIU/L are associated with increased risks for prematurity and neonatal respiratory distress syndrome, according to study results published in The Journal of Clinical Endocrinology & Metabolism.

The study included women aged ≥18 years with a singleton gestation and no known thyroid disease who were seen for prenatal care at Boston Medical Center in Massachusetts from January 2003 through May 2014 (N=8413; mean age, 29.1 years). Of all the women, 15% were white, 60% black, and 13% Hispanic. Median TSH level was 1.06 mIU/L (95% CI, 0.62-1.60 mIU/L), with 1.6% of women (n=130) having a TSH level >4 mIU/L. In their offspring, mean gestational age at birth was 38.5 weeks with a mean birth weight of 3.2 kg.

Compared with maternal TSH levels ≤4 mIU/L, maternal TSH levels >4 mIU/L were associated with increased risk for prematurity (risk ratio [RR], 2.17; 95% CI, 1.15-4.07; P =.016) and neonatal respiratory distress syndrome (RR, 2.83; 95% CI, 1.02-7.86; P =.046).

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The researchers also found nonstatistically significant associations between TSH levels >4 mIU/L and increased RRs for fetal loss, preeclampsia/eclampsia, and low birth weight. Maternal TSH levels >4 mIU/L were not associated with preterm labor, placental abruption, cesarean section, gestational hypertension/diabetes, or neonatal intensive care unit admission.

The researchers noted that their study was limited by potential selection bias and no available data on free thyroxine measurements or thyroid peroxidase antibody status for most patients.

“[M]ore interventional studies are needed to ascertain the benefit of treatment of maternal [subclinical hypothyroidism] in pregnancy,” the researchers wrote.

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Reference

Lee SY, Cabral HJ, Aschengrau A, Pearce EN. Associations between maternal thyroid function in pregnancy and obstetric and perinatal outcomes [published online December 15, 2019]. J Clin Endocrinol Metab. doi:10.1210/clinem/dgz275