RESUMEN
INTRODUCTION: The aim of this study was to construct a reference curve based on longitudinal Doppler blood flow measurements of the uterine artery during the first and second trimesters of normal pregnancy. MATERIAL AND METHODS: Healthy pregnant women (n = 124) between 18 and 38 years of age were included. The uterine artery pulsatility index (UtAPI) was measured with transvaginal ultrasound in the first trimester (gestational weeks 8-10 and 11-13) and with transabdominal ultrasound in the second trimester (gestational weeks 18 and 24). Individual longitudinal curves were constructed and a reference curve was created. RESULTS: A centile curve with the normal distribution of the UtAPI during the first and second trimesters was constructed. We found that 90% of the women alternated between quartiles during the four examinations between gestational weeks 8 and 24, but 75% remained within the higher or lower range. CONCLUSIONS: A UtAPI reference curve was constructed for the first and second trimesters of pregnancy. Although the mean UtAPI values may vary from one examination to the next, most mean UtAPI values remain within the higher or lower range, i.e. above or below the 50th centile.