Obesity in pregnancy causes a volume overload in third trimester

Abstract

Background Obesity is a major risk factor for cardiovascular diseases. In this study, we aimed to investigate the maternal circulatory differences during pregnancy between obese and normal weight women. Materials and methods The functioning of the maternal circulation (arteries, veins, heart and body fluid) was assessed by ECG‐Doppler ultrasound, impedance cardiography (ICG) and bio‐impedance during pregnancy in obese women (BMI ≥30 kg/m2) and normal weight, nonobese women (BMI 20‐25 kg/m2). In this observational study, 232 assessments were performed in the obese group, whereas 919 assessments were performed in the nonobese group. Results Relative to nonobese women, the overall cardiovascular function in obese women during first and second trimester is consistent with a high volume/low‐resistance circulation. In third trimester, cardiac output of obese women decreases from 9.2 (8.2‐10.7) L/min to 8.5 (7.6‐9.6) L/min (P = .037) whereas this is not true in the nonobese women (from 7.8 (7‐8.5) L/min to 7.8 (6.8‐8.9) L/min, P = .536). Simultaneously, the persistently lower peripheral vascular resistance in obese vs nonobese women disappears (880 (761‐1060) dyn.sec/cm5 vs 928 (780‐1067). Conclusions The circulatory gestational adaptations between nonobese and obese women were generally similar. The findings in the third trimester suggest that a pregnancy in obese women start as a state of high volume/low resistance, gradually shifting to a volume overload with decrease of cardiac output and disappearance of low vascular resistance. This evolution makes obese women vulnerable for gestational hypertensive diseases.

Preeclampsia has two phenotypes which require different treatment strategies

“…One explanation for this evolution is an endothelial dysfunction triggered by an intravascular overload with a subsequent increase in the vascular tone (peripheral vascular resistance) and a decrease in the cardiac output, as observed in pregnant women with obesity during an uncomplicated third trimester pregnancy. 25 Endothelial dysfunction caused by intravascular volume overload has been documented in nonpregnant individuals during hemodialysis 26 and acute heart failure. 27 For late-onset preeclampsia, frequently seen in women with obesity, high-output circulation is seen throughout all the stages of pregnancy, including the clinical stage of late-onset preeclampsia, during delivery, and postpartum 28 (Figure 2).…”

Hemodynamic pathways of gestational hypertension and preeclampsia

“…46 This observation is particularly evident in obese women, whose body water volume and cardiac output are constitutionally larger than those of normal-weight women. 47,48 The latter is considered to result from an increased intraabdominal pressure and external renal vein compression, leading to an increased glomerular capillary pressure with the activation of the juxtaglomerular apparatus and the reninAE angiotensinAEaldosterone system with subsequent sodium and water retention. 49 Gestational volume expansion superimposed on the constitutionally high intravascular volume of obese women is associated with a reduction of the cardiac output and an increase in the total vascular resistance during an uncomplicated third trimester pregnancy, an observation untrue for normalweight pregnant women.…”

The Possibility of Using Bioelectrical Impedance Analysis in Pregnant and Postpartum Women

“…Studying the mother's body composition and correlating it with her energy balance could facilitate the development of dietary recommendations for women that would help to ensure adequate weight gain dur-ing pregnancy. Obesity is a major risk factor for cardiovascular disease [91]. In the studies by Piuri et al it has been shown that women with hypertensive disorders caused by overweight and obesity had increased TBW and ECW already in early pregnancy [82].…”

“…BIA is also used as one of the additional tests in assessing the risk of developing GH and PE [68,69,75,91]. PE is a serious disease diagnosed in 2-8% of pregnancies [98,99], and it is associated with the risk of preterm labour.…”