Comparison of severe maternal morbidity between pregnancy with subclinical hypothyroidism and overt hypothyroidism

Maternal outcomes of pregnancy with subclinical hypothyroidism continue to be active areas of research interest. The objective of this study was to compare severe maternal morbidity at delivery between pregnant patients with subclinical hypothyroidism and those with overt hypothyroidism.

This cross-sectional study queried the Healthcare Cost and Utilization Project's National Inpatient Sample. Study population included 11 620 hospital deliveries with a diagnosis code of subclinical hypothyroidism and 697 320 hospital deliveries with a diagnosis code of overt hypothyroidism. Main outcome was severe maternal morbidity per the Centers for Disease Control and Prevention definition (20 indicators), assessed with multivariable generalized linear model.

Pregnancy with subclinical hypothyroidism was associated with a 54% higher rate of severe maternal morbidity at delivery compared with those with overt hypothyroidism (18.1 and 11.1 per 1000 deliveries, adjusted-incidence rate ratio [aIR] 1.54, 95% confidence interval [CI] 1.34-1.76). Among the individual severe maternal morbidity indicators, the incidence rate of eclampsia (2.2 versus 0.7 per 1000 deliveries, aIR 2.73, 95% CI: 1.83-4.09) was particularly higher among pregnancies with subclinical hypothyroidism compared with pregnancies with overt hypothyroidism. In an exploratory evaluation according to patient demographics, maternal age younger than 25 years (31.9 vs. 9.4 per 1000 deliveries, aIR 3.62, 95% CI: 2.62-5.01), Black individuals (55.2 vs. 24.7 per 1000 deliveries, aIR 2.21, 95% CI: 1.60-3.06), pregestational hypertension (70.2 vs. 27.2 per 1000 deliveries, aIR 2.20, 95% CI: 1.60-3.03), and obesity disorder (35.2 vs. 16.7 per 1000 deliveries, aIR 1.87, 95% CI: 1.48-2.35) were associated with higher rates of severe maternal morbidity for subclinical hypothyroidism compared with overt hypothyroidism. Severe maternal morbidity rates were more than twice as high for subclinical hypothyroidism compared with overt hypothyroidism among pregnant patients younger than 25 years with obesity disorder (79.4 vs. 10.1 per 1000 deliveries, aIR 7.89, 95% CI: 4.78-13.02), Black individuals with pregestational hypertension (157.9 vs. 40.2 per 1000 deliveries, aIR 3.15, 95% CI: 1.77-5.61), and Black individuals with obesity disorder (102.0 vs. 33.9 per 1000 deliveries, aIR 2.81, 95% CI: 1.83-4.32).

The results of this cross-sectional study suggest that subclinical hypothyroidism may be associated with higher rates of severe maternal morbidity at delivery compared with overt hypothyroidism.