Maternal cardiac function in normal twin pregnancy: a longitudinal study

Objective: To investigate maternal cardiac function in a cohort of uncomplicated twin gestations assessed longitudinally.

Methods: Women with twin pregnancies were enrolled prospectively and underwent serial maternal echocardiography at 20-23 weeks, 26-29 weeks and 30-33 weeks of gestation. Patients were excluded if any of these complications occurred after recruitment: delivery < 34 weeks; pre-eclampsia or gestational hypertension; small-for-gestational age neonates (birth weight of one or both twins < 5(th) centile for gestational age). Cardiac findings were compared with those obtained at the same gestational age periods in a group of singleton gestations.

Results: A group of 20 uncomplicated twin gestations was obtained for analysis and 10 singleton pregnancies were then selected as controls. At each visit, mean ± SD cardiac output (CO) was significantly higher in twins than in singletons (6.55 ± 0.82 vs 5.62 ± 0.82 L/min, P = 0.007 at 20-23 weeks; 7.31 ± 0.74 vs 6.39 ± 0.74 L/min, P = 0.003 at 26-29 weeks; 7.50 ± 0.89 vs 6.68 ± 0.65 L/min, P = 0.015 at 30-33 weeks), whereas total vascular resistance (TVR) was lower (1005 ± 137 vs 1179 ± 199 dynes × s/cm(5) , P = 0.009 at 20-23 weeks; 924 ± 100 vs 1070 ± 138 dynes × s/cm(5), P = 0.003 at 26-29 weeks; 929 ± 96 vs 1031 ± 122 dynes × s/cm(5), P = 0.018 at 30-33 weeks). In both twins and singletons, CO showed a significant increase while TVR decreased significantly throughout the assessed pregnancy time period.

Conclusion: In twin gestation, maternal cardiac function apparently undergoes more profound changes compared with in singleton gestation, as testified by higher CO and lower TVR values at each stage of pregnancy starting from the mid-trimester.