Impaired Maternal Hemodynamics in Morbidly Obese Women: A Case-control Study.

AIM: Maternal obesity is associated with significant pregnancy complications and is a risk factor for the development of hypertensive disorders of pregnancy as well as other adverse outcomes. There are few data regarding the hemodynamic aberrations observed in maternal obesity. The aim of this study was to investigate maternal hemodynamics in morbidly obese pregnant women. METHODS: This was a prospective, case-control study of morbidly obese women (BMI >40 kg/m(2) ) and controls (BMI 20-29.9 kg/m(2) ) at a ratio of one-to-ten. The control population was matched for maternal age and gestational age. BMI was calculated based on maternal height and weight at the time of recruitment to the study, which occurred on the same day as the hemodynamic assessment. Pregnant women in the second or third trimester of pregnancy were included. Women who were found to be hypertensive at any time were excluded from the study. USCOM-1A(®) was used to assess hemodynamic parameters (heart rate, stroke volume, cardiac output and systemic vascular resistance). The parameters were corrected for body surface area (BSA) to provide the stroke volume index (SVI), cardiac index (CI) and systemic vascular resistance index (SVRI). Mann Whitney-U test was used to compare the medians of the hemodynamic variables between the two groups. RESULTS: A total of 30 obese women and 327 controls were recruited. There was no difference in maternal (p = 0.506) or gestational (p = 0.693) age at recruitment between the groups. Mean arterial pressure was higher both at pregnancy booking (90 vs 80 mmHg, p < 0.001) and study recruitment (91 vs 85 mmHg, p < 0.001) in the obese group. Heart rate was higher in the obese group (p = 0.003), however there was no difference in stroke volume (p = 0.271), cardiac output (p = 0.238) or systemic vascular resistance (p = 0.635). Following correction of these parameters for BSA, the SVI (34 vs 45 ml/m(2) , p < 0.001) and CI (2.96 vs 3.64 L/min/m(2) , p < 0.001) were significantly reduced in the obese group, whilst the SVRI was significantly higher (2354 vs 1840 dynes-sec-cm(5) /m(2) , p < 0.001). CONCLUSION: The findings of our study suggest that cardiac function is significantly altered in morbidly obese pregnant women. In order to make appropriate comparisons between individuals, it is imperative that hemodynamic parameters are indexed for BSA - as indeed they are in pediatric cardiology. The novel finding of a reduced CI in morbidly obese pregnant women may explain the predisposition to preeclampsia and other adverse outcomes in this population and warrants further investigation