Longitudinal hemodynamic evaluation of uncomplicated twin pregnancies according to chorionicity: physiological cardiovascular dysfunction in monochorionic twin pregnancy.

OBJECTIVE: Maternal cardiac function plays a crucial role in normal placental function and development. The maternal hemodynamic changes in twin pregnancy are more pronounced than in singleton, presumably due to an increased plasma volume expansion. In view of the correlation between cardiac and placental function, it is plausible that chorionicity could influence maternal cardiac function. The aim of this study was to compare the longitudinal maternal hemodynamic changes in dichorionic and monochorionic twin pregnancies.

METHODS: 40 monochorionic diamniotic (MC), 35 dichorionic diamniotic (DC) uncomplicated twin pregnancies were included in the study. 531 healthy singleton pregnancies from a cross-sectional study are used as the control group. All participants underwent a hemodynamic evaluation using Ultrasound Cardiac Output Monitor (USCOM®) at three different stages in pregnancy (11-15 weeks, 20-24 weeks and 29-33 weeks) recording mean arterial pressure (MAP), stroke volume (SV), stroke volume index (SVI) heart rate (HR), cardiac output (CO), cardiac index (CI), systemic vascular resistance (SVR), systemic vascular resistance index (SVI), Stroke Volume Variation (SVV), Smith-Madigan Inotropy Index (INO) and potential to kinetic energy ratio (PKR).

RESULTS: Maternal CO (8.33 vs 7.30 l/min, p=0.03) and CI (4.52 vs 4.00 l/min/m2 , p=0.02) were significantly higher in the second trimester in MC compared to DC twin pregnancies. Women with MC twin pregnancies showed significantly higher PKR (24.06 vs 20.13, p=0.03) and SVRI (1837.20 vs 1698.49 d.s.cm-5 /m2 , p=0.03) in the third trimester, and significantly lower values of SV (78.80 vs 88.80 cm3 , p=0.01), SVI (47.00 vs 50.31 cm3 /m2 , p<0.01) and INO (1.70 vs 1.87 W/m2 , p=0.03) vs. singleton pregnancies. These differences were not observed in DC twin pregnancies.

CONCLUSIONS: Maternal cardiovascular function undergoes significant changes during an uncomplicated twin pregnancy and chorionicity influences maternal hemodynamics. In both twin pregnancies the hemodynamic changes are detected as early as the first trimester. In DC twin pregnancies the maternal hemodynamics remain stable during the rest of pregnancy. On the contrary, in MC twin pregnancies the rise in maternal CO continues in the second trimester to sustain the higher placental growth. There is a subsequent cross-over with a reduction in cardiovascular performance during the third trimester. This article is protected by copyright. All rights reserved.