The impact of maternal hypothyroidism on the prevalence of preeclampsia in a contemporary nationwide cohort
Authors: Alampoondi Venkataramanan S V , Li P , Hadley M , Cai P 
Published: October 2021

Abstract

Introduction
Hypothyroidism is common with a prevalence of 3.7% in the general population and 3.1% in women of childbearing age (12–49) in the United State of America (USA) according to the National Health and Nutrition Examination Survey. Studies have found an increased prevalence of hypertension in patients with hypothyroidism. However, there is a dearth of literature exploring the association between hypothyroidism and hypertensive disorders in pregnancy, especially preeclampsia. Our study aims to fill that void.

Purpose
To examine the association between hypothyroidism and preeclampsia.

Methods
We conducted a retrospective cohort study using the latest available data from the USA National Inpatient Sample (2016). Using the ICD-10 codes, we identified patients admitted with a primary diagnosis of delivery and classified them into two cohorts based on the presence or absence of hypothyroidism. We compared the prevalence of preeclampsia and eclampsia among the patient with and without hypothyroidism. We used propensity score matching for age, hypertension, hyperlipidemia, obesity, anemia, hyperthyroidism, sleep apnea, chronic kidney disease, and smoking and repeated the analysis.

Results
We identified 752,054 patients who were admitted for delivery from January 1, 2016 to December 31, 2016. Of these, 726,769 did not have hypothyroidism and 25,285 had hypothyroidism. In the unmatched cohort, 1,572 patients had preeclampsia (6.2%, p&lt;0.001) in the hypothyroidism group and 32,539 (4.5%, p&lt;0.001) patients had preeclampsia in the non-hypothyroidism group. In the unmatched cohort, there was a significantly higher proportion of obesity (13.8% vs 8.2%, p&lt;0.001) and diabetes (3.3% vs 0.9%, p&lt;0.001) in the hypothyroidism group compared to the non hypothyroidism group. There were 25,282 patients in each group after propensity score matching. In the matched cohort, the prevalence of preeclampsia was still high in the hypothyroidism group compared to the non hypothyroidism group (6.2% vs 4.9, p&lt;0.001). The LOS was longer in the hypothyroidism group compared to the non hypothyroidism group (2.99±2.90 vs 2.75±2.42, p&lt;0.001). There was no statistical difference in the prevalence of eclampsia between the two groups (26 patients vs 30 patients, p=0.688). The difference in outcomes of death, cardiac arrest, acute kidney injury, acute respiratory failure and stroke were not statistically significant between these two groups.

Conclusion
Our study shows that hypothyroidism is associated with an increased prevalence of preeclampsia. The association existed even after propensity score matching for other common risk factors for preeclampsia. Given the retrospective nature of the study, we could not establish causation. Further prospective studies are required to find out if hypothyroidism leads to increased incidence of preeclampsia and if patients from hypothyroidism would benefit from prophylaxis for preeclampsia.

Funding Acknowledgement
Type of funding sources: None. Study design