Relationship of uterine blood flow to chorionic sac and embryo growth rates

The embryonic period of development is characterized by marked variability in the rate of embryonic growth and development. Differences in uterine blood flow may explain this variability. We investigated the relationship between uterine artery blood flow volume (VOL), uterine artery pulsatility index (UA-PI), uterine artery resistance index (UA-RI), spiral artery pulsatility index (SA-PI), spiral artery resistance index (SA-RI), chorionic sac diameter (CSD), and crown-rump length (CRL) during 321 first trimester vaginal colour Doppler ultrasound examinations of 94 delivered or continuing pregnancies. After correcting for the confounding effect of gestational age, subject, and serum hormone levels by Analysis of Covariance, CRL was related to UA-PI (P = 0.025) and UA-RI (P < 0.001), but not to VOL, SA-PI, or SA-RI. No relationship was found between CSD and any uterine blood flow variables. Serum oestradiol levels were related to CSD and CRL (P < 0.001). No relationship was found to progesterone, maternal age, parity, or previous abortion. We conclude that differences in uterine blood flow and serum oestradiol explain some of the variability in the rate of embryo growth during the first 12 gestational weeks.