Doppler indices of the umbilical and fetal middle cerebral artery at 18-40 weeks of normal gestation: A pilot study

Doppler indices form an integral component of noninvasive evaluation of fetal well-being. There is paucity of information about normal obstetric Doppler indices, particularly from the Indian subcontinent. The aim of the study was to find the values of pulsatility index (PI), resistive index (RI) of umbilical artery (UA), and fetal middle cerebral artery (MCA) and calculate cerebro-placental ratio (CP ratio) for 18-40 weeks of normal gestation so that a reference range of these Doppler values can be postulated.

200 patients were enrolled in the study for color Doppler study of UA and MCA and were serially followed up at 4-6 weeks interval for Doppler indices. Angle-independent Doppler indices like PI and RI for MCA and UA were obtained during each examination. CP ratio was calculated in each case. All the cases were followed up till delivery and the perinatal outcome was recorded.

The fetal MCA PI and RI showed a parabolic curve with plateau at 28-30 weeks of gestation. A significant correlation was noted between MCA PI and RI with gestational age. UA PI and RI showed a gradual fall over the gestational age with a strong negative correlation. There was a significant correlation between MCA PI and UA PI with their respective RI values. CP ratio has also shown a parabolic curve with turning point at 31-32 weeks of gestation. A significant correlation was noted between CP ratio and gestational age. CP ratio also showed a minimal positive correlation with MCA PI and a strong negative correlation with UA PI.