Association of maternal body mass index with hemodynamic and vascular alterations at 35-37 weeks' gestation

Globally, one in four pregnant women is classified as overweight or obese, based on their prepregnancy body mass index (BMI). Obese pregnant women are at increased risk of adverse pregnancy outcomes and long-term cardiovascular disease that occurs earlier in life. This study aimed to assess maternal hemodynamic and vascular parameters at 35-37 weeks' gestation, to understand the alterations that may occur in association with increased maternal BMI and gestational weight gain, and to evaluate obesity-related pregnancy outcomes.

This was a prospective observational study of 11 731 women with a singleton pregnancy attending for a routine hospital visit at 35 + 0 to 36 + 6 weeks' gestation at King's College Hospital, London, UK, between December 2021 and June 2024. Women were categorized based on their BMI at 11-13 weeks' gestation, as normal weight (BMI, 18.5-24.9 kg/m²), overweight (BMI, 25.0-29.9 kg/m²) or obese (BMI, ≥ 30 kg/m²). We recorded details regarding maternal demographic characteristics and medical history, used Doppler ultrasound to assess the uterine artery pulsatility index (UtA-PI) (as a marker for uteroplacental perfusion) and ophthalmic artery peak systolic velocity (PSV) ratio (as a marker for small vessel peripheral circulation), and measured carotid-to-femoral pulse-wave velocity, augmentation index (as direct and indirect markers of aortic stiffness, respectively), cardiac output, total peripheral resistance (TPR), and central systolic and diastolic blood pressure. Multivariable analysis was performed to examine the relationship of BMI and gestational weight gain with hemodynamic and vascular measures, adjusting for maternal demographics, medical history, pregnancy characteristics and pregnancy outcomes (including pre-eclampsia and gestational diabetes mellitus).

Overweight and obese women were more often of black ethnicity, and had higher central systolic and diastolic blood pressure, cardiac output, aortic stiffness and UtA-PI, compared with normal-weight women. There was no significant difference between overweight or obese women and normal-weight women with regard to TPR and ophthalmic artery PSV ratio. On multivariable analysis, increasing BMI at 11-13 weeks and gestational weight gain between 11-13 weeks and 35-37 weeks were independently associated with increases in all cardiovascular indices (including ophthalmic artery PSV ratio), apart from TPR.

Women with a high BMI in early pregnancy vs normal-weight women, and those with higher gestational weight gain, had worse maternal hemodynamic and vascular indices at 35-37 weeks' gestation, independent of baseline and pregnancy characteristics. Our findings support the notion that optimization of prepregnancy weight and gestational weight gain may improve maternal hemodynamics and vascular function during pregnancy, and therefore may improve pregnancy outcomes. © 2025 The Author(s). Ultrasound in Obstetrics & Gynecology published by John Wiley & Sons Ltd on behalf of International Society of Ultrasound in Obstetrics and Gynecology.