Subclinical hypothyroidism is not associated with neonatal morbidity in women with gestational diabetes mellitus: a case-control study

Purpose Placental modifications observed in women with subclinical hypothyroidism (SCH) should be associated with altered fetal development in women with gestational diabetes mellitus (GDM) and worsen perinatal outcome. We aim to determine if SCH is associated with neonatal morbidity in women with GDM. Methods A secondary analysis of data collected for a prospective population-based cohort study including all pregnant women with singleton pregnancies at diagnosis of GDM in a tertiary care university hospital. Thyroid-stimulating hormone and free thyroxine were measured at diagnosis of GDM. Perinatal outcome was compared between two groups-women with SCH and euthyroid. Neonatal morbidity was defined by at least one of the following criteria: preterm birth, macrosomia, shoulder dystocia, respiratory distress syndrome, 5-min Apgar score < 7, pH < 7.10, and admission to the NICU (neonatal intensive-care unit) for 24 h. Results Of the total 200 women enrolled, 150 were evaluable for the study. Of whom, 9 (6%) women presented SCH. The mean gestational age at diagnosis of GDM was 21.7 +/- 7.0 weeks. Maternal outcome of women with SCH was similar to euthyroid women. Neonatal morbidity occurred in 17.3% (26/150). Women with SCH had higher rate of neonatal morbidity (44.4%vs.15.6%;p = 0.03), specifically due to admission to the NICU for 24 h (33.3%vs.5.7%;p = 0.02). SCH in women with GDM is not associated with neonatal morbidity after controlling for gestational age at birth and admission to NICU (adjusted OR 2.02, 95% CI 0.75-10.23). Conclusion Subclinical hypothyroidism is not associated with neonatal morbidity in women with gestational diabetes mellitus.