First-trimester uterine artery blood flow and birth weight.

OBJECTIVES

To determine reference values for first-trimester uterine artery resistance index (RI) in healthy pregnant women with uncomplicated pregnancies and to investigate the relationship between uterine artery Doppler indices and birth weight.

METHODS

This was a cross-sectional study of 265 consecutive pregnant women attending routine ultrasound examination at 11-14 weeks' gestation. Both uterine arteries were identified using color Doppler ultrasound and the RI was measured. The presence or absence of an early diastolic notch was also noted. Pregnancy outcomes were obtained from the delivery suite database and birth weight was expressed as Z-scores.

RESULTS

The 5(th), 50(th) and 95(th) centiles for uterine artery RI between 11 and 14 weeks' gestation were 0.53, 0.71 and 0.85, respectively. Complete pregnancy outcome data were available for 246 fetuses. There was a significant negative correlation between birth-weight Z-scores and first-trimester uterine artery mean RI (r = - 0.219, P = 0.001). The difference in birth weight between fetuses with absent and those with bilateral diastolic notches was also significant (P < 0.001). Multiple regression analysis demonstrated that both mean RI (standardized regression coefficient = - 0.14, P = 0.039) and uterine artery notching (standardized regression coefficient = - 0.17, P = 0.017) contributed independently towards the prediction of birth-weight Z-score.

CONCLUSIONS

A significant negative correlation exists between birth weight and first-trimester uterine artery Doppler parameters, a reliable and non-invasive method of examining uteroplacental perfusion. The value of first-trimester uterine artery Doppler as a prognostic screening tool, either in isolation or in conjunction with maternal biochemistry, remains to be determined.