Doppler ultrasound of the maternal uterine arteries: disappearance of abnormal waveforms and relation to birthweight and pregnancy outcome

Background. To assess whether the gestation at which abnormal uterine artery waveforms disappear is related to birthweight and complications of pregnancy. Methods. A prospective study of outcome of pregnancy after a uterine artery Doppler screening program set in an inner city teaching hospital. One thousand five hundred and twenty-four consecutive women attending the Obstetric Department for a routine anomaly scan at between 19 and 21 weeks gestation had maternal uterine arteries assessed using color wave Doppler. Those women in whom the flow was deemed abnormal were recalled for a further scan at 24-26 weeks gestation. The main outcome measures were birthweight, gestation at delivery and incidence of pre eclampsia. Results. The women in whom the uterine artery blood flow was normal at 20 weeks had babies with significantly higher mean birthweight than those who normalized between 20 and 24-26 weeks gestation ('late normalizers') after adjustment for confounding factors; gestational age, maternal height, parity, ethnic group and smoking (mean difference = 173 g, 95% confidence intervals 42 to 303 g). Conclusions. The timing of trophoblast invasion, as reflected by abnormal uterine artery waveforms, may have an effect on birthweight.