THE EFFECT OF FETAL HEART-RATE AND FETAL ACTIVITY ON THE MIDDLE CEREBRAL-ARTERY FLOW VELOCITY WAVE-FORMS IN NORMAL HUMAN FETUSES FROM 18 TO42 WEEKS GESTATION

Objectives: The purpose of the study was to evaluate the effect of fet al heart rate (FHR) and fetal activity (FA) on the pulsatility index ( PI) of fetal middle cerebral artery (MCA). Methods: We examined 181 no rmal pregnant women from 18 to 42 weeks gestation with pulsed wave Dop pler and color flow Doppler. Fetal activity was determined by ultrasou nd. Results: The fetal MCA PI declines with advancing gestation after 25 weeks. MCA PI is significantly higher in the second than in the thi rd trimester whereas the FHR is similar. MCA PI values are normally di stributed and correlate best with gestational age and least with FHR b ut not at all with fetal activity (FA). Simple linear regression of MC A PI on FHR according to FA revealed this correlation to be stronger i n active fetuses. During the second trimester, the MCA PI is lower in active than in quiet fetuses. In the third trimester, this difference is smaller. FHR shows similar responses in the two activity states. FH R in the entire group, however, is higher in active fetuses but MCA PI is similar in the two activity states. Conclusions: Fetal MCA PI decl ines with advancing gestation significantly in the presence of an insi gnificant decline of the FHR. FHR and MCA PI relate differently in act ive than in quiet fetuses. The effect of activity on FHR and MCA PI is variable in second and third trimester fetuses.