Monitoring early pregnancy with transvaginal ultrasound and choriogonadotrophin levels.

Serum human chorionic gonadotrophin levels were correlated with gestational sac size detected by transvaginal ultrasound in a series of 178 women undergoing in vitro fertilization. The improved resolution of transvaginal ultrasound enables pregnancy to be detected between 17 and 20 days post-ovum retrieval, when HCG levels were greater than an average threshold level of 1,300 IU/L. The lower HCG discriminatory zone enables improved evaluation of ectopic pregnancies. Also, higher HCG titres observed in multiple pregnancies enable estimation of implantation rates when more than one embryo is transferred.