O-164 Associations between hypothyroidism and adverse obstetric and neonatal outcomes: a population study of 9.1 million births
Authors: Hizkiyahu R , Badeghiesh A , Baghlaf H , Dahan M H 
Published: August 2021

Study question

Does hypothyroidism confer an independent risk for adverse delivery and neonatal outcomes, based on analysis of the Healthcare Cost and Utilization Project-Nationwide Inpatient Sample database?

Summary answer

After controlling for confounders, women with hypothyroidism are at an increased risk of hypertensive disorders of pregnancy, preterm delivery, placental abruption, hemorrhage and caesarean section.

What is known already

Surprisingly, studies in the literature on maternal and neonatal complications of hypothyroidism in pregnancy are relatively small. The largest study to date included 184,611 pregnancies overall, with 7140 with hypothyroidism. Maternal hypothyroidism has been associated with multiple adverse pregnancy outcomes. These findings have not been confirmed in a large population database study.

Study design, size, duration

This is a retrospective study utilizing data from the Healthcare Cost and Utilization Project-Nationwide Inpatient Sample (HCUP-NIS). A cohort of all deliveries between 2004 and 2014 inclusively was created. Within this group, all deliveries to women with hypothyroidism formed the study group (n = 185,073), and the remaining deliveries were categorized as non- hypothyroidism births and comprised the reference group (n = 8,911,715). The main outcome measures were pregnancy and perinatal complications. Patients were included once per pregnancy.

Participants/materials, setting, methods

The HCUP-NIS is the largest inpatient sample database in the USA. It provides information relating to seven million inpatient stays per year, includes ∼20% of hospital admissions, and represents over 96% of the American population. Multivariate logistic regression analysis, controlling for confounding effects, was conducted to explore associations between hypothyroidism and delivery and neonatal outcomes. According to Tri-Council Policy statement (2018), IRB approval was not required, given data was anonymous and publicly available.

Main results and the role of chance

Women with hypothyroidism were more likely to be older than 25 years, Caucasian, have higher household incomes, private insurance and deliver in an urban teaching hospital, as compared with the non-hypothyroidism obstetrical population (p &lt; 0.0001, all cases). After adjustment for all statistically significant confounders, women with hypothyroidism were more likely to suffer from gestational diabetes mellitus (aOR 1.43, 95%CI 1.38-1.47), hypertensive disorders of pregnancy: gestational hypertension (aOR 1.17, 95%CI 1.11-1.22) and preeclampsia (aOR 1.21, 95%CI 1.16-1.27) (all P &lt; 0.001)). They were more likely to experience PPROM (aOR 1.19, 95%CI 1.09-1.29) and preterm delivery (aOR 1.12 95%CI 1.08-1.17), and deliver by caesarean section (aOR 1.21, 95% CI 1.18-1.24 (all P &lt; 0.001)). Women with hypothyroidism more often developed chorioamnionitis (aOR 1.09, 95%CI 1.01-1.17, P = 0.019), maternal infections (aOR 1.08, 95% CI 1.01-1.16, P = 0.017), post-partum hemorrhage (aOR 1.07, 95%CI 1.01-1.13, P = 0.012), disseminated intravascular coagulation (aOR 1.20, 95%CI 1.00-1.43, P = 0.047), require blood transfusions (aOR 1.12, 95%CI 1.03-1.22, P = 0.009), and hysterectomy (aOR 1.42, 95% CI 1.13-1.80, P = 0.012) compared to the control group. [HB1] As for neonatal outcomes, small for gestational age and congenital anomalies were more likely to occur in the offspring of women with hypothyroidism (aOR 1.20, 95% CI 1.14-1.27 and aOR 1.34, 95% CI 1.22–1.48, both P &lt; 0.001).

Limitations, reasons for caution

This is a retrospective analysis utilizing an administrative database that relies on data coding accuracy and consistency.

Wider implications of the findings

Women with hypothyroidism were more likely to experience pregnancy, delivery and neonatal complications. We found an association between hypothyroidism and; hypertensive disorders, post-partum hemorrhage, transfusions, infections, preterm deliveries and hysterectomy, among other problems. This data from a population sized database confirmed the findings of the smaller studies in the literature.

Trial registration number

not applicable