The Cardio-Feto-Placental unit: fetal umbilical vein flow rate is linked to the maternal cardiac profile in fetal growth restriction.

BACKGROUND: The functional maternal-fetal hemodynamic unit includes fetal umbilical vein flow and maternal peripheral vascular resistance.

OBJECTIVE: We investigated the relationships between maternal and fetal hemodynamics in a population with suspected fetal growth restriction.

STUDY DESIGN: This was a prospective study of normotensive pregnancies referred to our outpatient clinic for a suspected fetal growth restriction. We performed a maternal hemodynamics measurement, using a non-invasive device (USCOM-1A®), and a fetal ultrasound evaluation to assess fetal biometry and velocimetry Doppler parameters. Comparisons among groups were performed with 1-way analysis of variance with Student-Newman-Keuls correction for multiple comparisons and with Kruskall-Wallis test where appropriate. Spearman's rank coefficient was used to assess the correlation between maternal and fetal hemodynamics. Pregnancies were followed until delivery.

RESULTS: 182 normotensive pregnancies were included. After the evaluation 54 fetuses were classified as growth restricted, 42 as small for gestational age, and 86 as adequate for gestational age.Growth-restricted fetus had significantly lower umbilical vein diameter (P<0.0001), umbilical vein velocity (P=0.02), umbilical vein flow (P<0.0001), and umbilical vein flow corrected for fetal weight (P<0.01) compared with adequate and small for gestational age fetuses. The maternal hemodynamic profile in fetal growth restriction was characterized by elevated systemic vascular resistance and reduced cardiac output.The umbilical vein diameter was positively correlated to maternal cardiac output (rs =0.261), whereas there was a negative correlation with maternal systemic vascular resistance (rs =-0.338) and maternal potential to kinetic energy ratio (rs =-0267). The fetal umbilical vein time averaged max velocity was positively correlated to maternal cardiac output (rs =0.189) and maternal Inotropy Index (rs =0.162), whereas there was a negative correlation with maternal systemic vascular resistance (rs =-0.264) and maternal potential to kinetic energy ratio (rs =-0.171). The fetal umbilical vein flow and the flow corrected for estimated fetal weight were positively correlated with maternal cardiac output (rs =0.339 and rs =0.297) and maternal inotropy index (rs =0.217 and r=0.336), whereas there was negative correlation with maternal systemic vascular resistance (rs =-0.461 and rs =-0.409) and maternal potential to kinetic energy ratio (rs =-0.336 and rs =-0.408).

CONCLUSION: Maternal and fetal hemodynamic parameters are different in the three groups of fetuses: fetal growth restriction, small for gestational age and adequate for gestational age. Maternal hemodynamic parameters are closely and continuously correlated with fetal hemodynamic features. In particular, a maternal hemodynamic profile with high systemic vascular resistance, low cardiac output, reduced inotropism and hypodynamic circulation is correlated with a reduced umbilical vein flow and increased umbilical artery Pulsatility index. The mother, the placenta and the fetus should be considered as a single cardio-feto-placental unit. The correlations of systemic vascular resistance, cardiac output, and inotropy index with umbilical artery impedance indicate the key role of these three parameters in placental vascular tree development. The umbilical vein flow rate and, therefore, the placental perfusion appears to be influenced not only by these three parameters, but also by the maternal cardiovascular kinetic energy.