Fetal Doppler reference values in women with a normal body mass index

To construct gestation specific reference limits for fetal umbilical (UA), middle cerebral artery (MCA) pulsatility indices (PI) and the cerebroplacental ratio (CPR) in singleton pregnancies with normal BMI between 16 and 40 weeks of gestation.

We ultrasonographically examined 596 fetuses from women with normal nutritional and health status and minimal environmental constraints on fetal growth. Each mother was considered only once for measurement of fetal Doppler indices, at gestations between 16 and 40 weeks in a prospective cross-sectional study. Gestational age was confirmed by fetal crown-rump length measurement between 11 and 14 weeks. Pulsatility indices of umbilical and middle cerebral arteries were measured by real time and Doppler ultrasonography. CPR ratio was calculated by dividing MCA PI by UA PI. The fetal Doppler measurements obtained from the current study were compared with commonly used reference charts. For each parameter separate polynomial regression models were fitted to estimate the gestation specific means and standard deviations, assuming that the measurements have a normal distribution at each gestational age.

A significant difference of fetal Doppler indices was observed between our study and previously published reference charts for most gestational weeks. The fitted 10th, 50th and 90th centiles at 40 weeks of gestation were 0.65, 0.87 and 1.08 for UA PI; 0.93, 1.32 and 1.71 MCA PI; 1.02, 1.58 and 2.13 for CPR.

These charts can be used for better defining the normal range of fetal arterial Doppler indices. This will be useful in the diagnosis and management of fetuses with abnormal fetal growth.