Effect of parity on maternal cardiac function during the first trimester of pregnancy.

OBJECTIVE To investigate maternal cardiac adaptation in the first trimester of pregnancy with increasing maternal parity. METHODS This was a cross-sectional study carried out at the antenatal clinic of a teaching hospital. We examined 4689 pregnant women at 11 + 0 to 13 + 6 weeks of gestation, performing two-dimensional echocardiography of the maternal left ventricle. There were 2352 parous and 2337 nulliparous women. The relationships between parity, maternal cardiac function and neonatal birth weight were analyzed. RESULTS Parous compared to nulliparous women had a significantly higher median cardiac output (5.6 vs. 5.2 L/min) and median cardiac index (2.3 vs. 2.1 L/min/m(2)). This was owing to a significantly higher median stroke volume (73.5 vs. 70.5 mL), heart rate (76 vs. 75 bpm), left ventricular outflow diameter (20.4 vs. 20.0 mm) and lower total vascular resistance (1190.8 vs. 1253.7 dyne s/cm(5)) and median uterine artery pulsatility index (1.6 vs. 1.7). Mean arterial blood pressure was not significantly different between the groups. There was a progressive increase in all maternal cardiac variables, apart from total peripheral resistance, which decreased with increasing parity. Birth weight was higher in parous compared to nulliparous women (3.39 vs. 3.23 kg) and it was independently related to maternal hemodynamic variables and demographic and social characteristics (age, height, weight, ethnicity, smoking). CONCLUSION Pregnancy in parous compared to nulliparous women is characterized by higher maternal cardiac output and birth weight.