Montenegro, N, J C Areias, and L P Leite. 1993. “Transvaginal Endosonography and Doppler Study in Embryo-Fetal Hemodynamic Assessment in the First Pregnancy Trimester”. Acta Médica Portuguesa 6 (December). Lisbon, Portugal:I3-8. https://doi.org/10.20344/amp.3177.