A cross-sectional study was performed in 85 low-risk singleton first t
rimester pregnancies to assess corpus luteum blood flow during this pe
riod. Gestational age, established by measuring crown-rump length, ran
ged from 6 to 12 weeks. All cases were studied by transvaginal color v
elocity imaging and pulsed Doppler ultrasonography. After corpus luteu
m blood flow was identified by color velocity imaging, the resistive i
ndex and pulsatility index were calculated to assess vascular resistan
ce. Overall, detection rate of corpus luteum blood flow was 75.2%. No
statistical differences were found in mean resistive index and pulsati
lity index among gestational weeks studied. Linear regression analysis
showed that nonsignificant changes in resistive and pulsatility indic
es occur during the first weeks of normal early pregnancy (R(2) = 0.00
59 for resistive index, R(2) = 0.0008 for pulsatility index). In concl
usion, luteal blood flow is constant during normal early pregnancy.