Acute centralization of blood flow in compromised human fetuses evoked by uterine contractions.

BACKGROUND During fetal hypoxia blood is redistributed to the brain ('brain-sparing'). Sequential changes of the cerebral and placental circulation in parallel in comparisons between basal conditions and acute hypoxic stress have not yet been thoroughly studied in human fetuses. AIM To explore acute fetal middle cerebral artery (MCA) circulatory changes relative to umbilical artery (UA) blood flow in a clinical experimental model with hypoxic stress provoked by uterine contractions during an oxytocin challenge test (OCT). STUDY DESIGN Prospective comparative between imminently compromised (OCT positive) and un-compromised (OCT negative) fetuses. SUBJECTS AND METHODS 82 term pregnancies suspected of intrauterine growth restriction were exposed to simultaneous electronic fetal heart rate monitoring and Doppler recordings of pulsatility index (PI) in the UA and MCA during basal conditions and during uterine contractions and relaxations at an OCT. OUTCOME MEASURES Sequential changes of UA and MCA PI, OCT positive vs. negative cases. Nonparametric statistics with a P < 0.05 considered significant. RESULTS The UA PI was significantly higher in OCT positive cases (N = 10) compared with OCT negative cases (N = 72) during uterine contractions and relaxations, but not during basal measurements. During contractions and relaxations the MCA PI decreased significantly in both groups (brain-sparing), but significantly more in OCT positive cases. CONCLUSIONS During acute hypoxic stress, changes towards a centralization of blood flow to the brain develop in imminently compromised (OCT positive) fetuses at an expense of the umbilicoplacental blood flow, and the brain-sparing flow is more pronounced than in un-compromised (OCT negative) fetuses.