Early detection of pregnancy with transvaginal ultrasound.

The gestational age and the serum human chorionic gonadotropin (hCG) at which an intrauterine pregnancy can be detected using transvaginal ultrasonography (TVU) is not known. In this study, ten pregnant women were serially scanned with TVU from the time of initial positive pregnancy test, to determine when an intrauterine sac greater than 2 mm, fetal pole greater than 2 mm, and fetal heart motion could be detected. A gestational sac was seen 34.8 +/- 2.2 days from the last menstrual period (LMP), at which time the hCG was 1398 +/- 155 mIU/ml of the International Reference Preparations (IRP) or 914 +/- 106 mIU/ml of the Second International Standard (second IS). A fetal pole was seen 40.3 +/- 3.4 days from the LMP when the hCG was 5113 +/- 298 mIU/ml of the IRP or 3783 +/- 683 mIU/ml of the second IS. Fetal heart motion was detected 46.9 +/- 6.0 days from the LMP when the hCG was 17,208 +/- 3772 mIU/ml of the IRP or 13178 +/- 2898 mIU/ml of the second IS. From these results, it can be concluded that transvaginal ultrasonography can detect an intrauterine gestation earlier than what has been previously reported with transabdominal ultrasonography.