Central and peripheral haemodynamic changes in post-term fetuses: correlation with oligohydramnios and abnormal fetal heart rate pattern.

OBJECTIVE

To assess the hypothesis that the occurrence of oligohydramnios and abnormal fetal heart rate (FHR) pattern in post-term fetuses is associated with impaired fetal cardiac function.

DESIGN

A cross sectional study was performed on post-term and term fetuses. Fetal tests included a computerised analysis of the FHR, a biophysical profile and Doppler studies of the abdominal aorta, umbilical artery, middle cerebral artery and the fetal heart. Pulsatility index (PI) was calculated from the abdominal aorta, umbilical and middle cerebral artery flow velocity waveforms. Peak velocity, velocity time integral (VTI), E:A ratio, and heart rate (HR) were calculated from the flow velocity waveforms obtained from the aortic and pulmonic outflow, and from the mitral and tricuspid valves.

SETTING

Maternal fetal laboratory, Department of Obstetrics.

SAMPLE

One hundred and twenty post-term and 42 term fetuses.

RESULTS

Only the tricuspid E:A ratio was significantly higher (P < 0.05) in post-term fetuses with a normal amniotic fluid index compared with term fetuses. Post-term fetuses with an abnormal amniotic fluid index had a significantly lower aortic peak velocity (P < 0.01), aortic VTI x HR (P < 0.01), and mitral VTI x HR (P < 0.05) compared with post-term fetuses with a normal amniotic fluid index or compared with term fetuses. Post-term fetuses with reduced FHR variation had a significantly lower aortic peak velocity (P < 0.01), pulmonic peak velocity (P < 0.05), aortic VTI x HR (P < 0.01), pulmonic VTI x HR (P < 0.05) and a significantly lower mitral VTI x HR (P < 0.05) when compared with post-term fetuses with normal FHR variation. Similar results were obtained in comparing fetuses with normal and adverse perinatal outcome.

CONCLUSION

The occurrence of oligohydramnios and abnormal FHR pattern in post-term fetuses appears to be associated with impaired fetal cardiac function. This finding should allow further investigations of post-term fetuses.