Low cardiac output to the placenta: an early hemodynamic adaptive mechanism in intrauterine growth restriction.

OBJECTIVE

A low combined cardiac output (CCO) to the placenta (placenta/CCO fraction) has been reported in growth-restricted (IUGR) fetuses, but the temporal sequence of these modifications in relation to other changes in the fetal circulation is unknown. The aim of this study was to evaluate the placenta/CCO fraction in relation to other hemodynamic changes in fetuses at risk of developing IUGR.

METHODS

We studied 340 singleton nulliparous pregnancies characterized at 20-24 weeks by abnormal uterine artery pulsatility index (PI) values (> 95(th) centile). At this gestational age we measured fetal biometry and Doppler waveforms from the umbilical artery (UA), middle cerebral artery (MCA), ductus venosus (DV), umbilical vein (UV) and outflow tracts of both ventricles. The diameters of the semilunar valves and UV were measured and CCO (left cardiac + right cardiac outputs) and UV blood flow were calculated. The placenta/CCO fraction was calculated as UV flow as a percentage of CCO.

RESULTS

There were 283 pregnancies with birth weight >or= 10(th) centile and normal UA-PI throughout gestation (Group A), 34 with birth weight < 10(th) centile and normal UA-PI throughout gestation (Group B) and 23 with birth weight < 10(th) centile and abnormal UA-PI developing later in gestation (Group C). At 20-24 weeks there were no differences among the three groups in fetal biometric parameters, PI values from the UA, MCA and DV, and CCO. UV flow and placenta/CCO fraction were significantly lower in Group C compared with Group A (UV flow delta value = - 1.439, P < 0.0001; placenta/CCO fraction delta value = - 1.74, P < 0.0001) but not in Group B.

CONCLUSIONS

Our data suggest that, in fetuses developing IUGR secondary to placental compromise, UV flow and placental/CCO fraction are already reduced by 20-24 weeks, and that this reduction occurs earlier than do modifications in fetal size and arterial and venous PI values.