The additive effect of interpregnancy interval and maternal body mass index on pregnancy induced hypertension in the U.S.

Objectives: The incidence of pregnancy induced hypertension (PIH), one of the most frequent causes of maternal and neonatal morbidity, has increased significantly in the U.S. in last two decades. However, reasons for this rise are not well explored. The interrelationship between interpregnancy interval (IPI), prepregnancy body mass index (BMI), and PIH might play a role in this rise. This study aims to investigate the additive effect of IPI and prepregnancy BMI on PIH.

Study Design: The 2018 Vital Statistics Natality Data was analyzed (N = 1,046,350) for this cross-sectional study. A combined variable was created using IPI and prepregnancy BMI. Adjusted odds ratios and 95% confidence intervals were generated for IPI, prepregnancy BMI, and PIH using multiple logistic regression models.

Main Outcome Measure: PIH was defined using the birth certificate variable 'Gestational hypertension- (PIH, preeclampsia)' in the dataset.

Results: IPI and prepregnancy BMI were statistically significantly associated with PIH, both independently and in combination, after adjusting for potential confounders. The largest effect size was observed among women with long IPI and obesity (Adjusted OR = 4.01, 95% CI = 3.84, 4.25). Further, short IPI in combination with underweight BMI was found to be inversely associated with PIH (AOR = 0.64, 95% CI = 0.53, 0.78).

Conclusions: When combined, IPI and BMI are crucial risk factors for PIH. The highest risk of PIH is in women with long IPI in combination with high BMI categories. Healthcare professionals should be cognizant of the additional increased risk of PIH for the overweight and obese women with long IPI.