Vaginal sonography versus serum human chorionic gonadotropin in early detection of pregnancy.

We first performed a vaginosonic scan and then determined the serum human chorionic gonadotropin (beta-hCG) concentration (Second International Standard) in 52 women at an early gestational age to establish criteria for the earliest possible identification of an intrauterine pregnancy by this new ultrasound technique. The smallest diameter of a gestational sac detected was 2 mm, and the lowest beta-hCG concentration was 141 mIU/ml when an intrauterine pregnancy was correctly diagnosed. Between 50 and 280 mIU/ml, six out of eight pregnancies in this range were not seen. However, all pregnancies associated with beta-hCG concentrations greater than 300 mIU/ml were correctly identified. Taking into account the rapid growth of the conceptus and the exponential increase of serum beta-hCG by a factor of 1.7 per day at this early gestational age, we presume that a gestational sac at beta-hCG concentrations of 750 mIU/ml should not be missed by vaginosonography (safety margin of the discriminatory zone), even in instances of a retroverted uterus. No false-positive vaginosonographic findings were observed in this study. A vaginosonographic examination is a short and well-tolerated procedure that can be performed in a physician's office. The use of a 5 MHz transducer placed in the vagina provides better resolution and image quality. This overcomes imperfect anatomy and other physical factors that interfere with good imaging. The vaginosonographic examination provides information on the anatomic location of the gestational sac, with the highest reliability and accuracy around the time a woman misses her menstrual period. It can be very useful in the differential diagnosis of an ectopic pregnancy.