ABSTRACT
<p><b>OBJECTIVE</b>To explore the pattern of variations in middle cerebral artery peak systolic velocity (MCA PSV) and cardiothoracic ratio (CTR) during early pregnancy, establish their reference ranges and explore their correlation with the crown-rump length (CRL).</p><p><b>METHODS</b>A total of 522 pregnant women with normal findings in antenatal examinations underwent routine color Doppler ultrasound examination to collect the data of MCA PSV, CTR and CRL. The reference ranges of MCA PSV and CTR for different CRL levels were established, and the correlation of MCA PSV and CTR with CRL was analyzed.</p><p><b>RESULTS</b>During the first trimester, MCA PSV and CRL showed a moderate positive correlation with a correlation coefficient of 0.426 (P<0.001), while CTR and CRL showed no significant correlation (0.168, P<0.001). The reference range of MCA PSV was 14.35 (14.08-14.62) cm/s and that of CTR was 0.34 (0.33-0.34) during early pregnancy.</p><p><b>CONCLUSION</b>Color Doppler ultrasound is a safe and feasible modality to assess fetal MCA PSV and CTR for detecting fetal growth abnormalities in early pregnancy. The established reference ranges of MCA PSV and CTR offer a clinical theoretical basis for detecting α-thalassemia in early pregnancy.</p>