Value of "minimum menstrual age" in determining early pregnancy failure.
The purposes of this study were to assess a discriminatory "minimum menstrual age" (28 days + number of days elapsed between the first positive pregnancy test result and sonogram) for the diagnosis of early pregnancy failure when no embryonic/fetal heartbeat is seen and to compare minimum menstrual age dating with last menstrual period and sonographic dating. We conducted a retrospective study of 338 initial first-trimester sonographic examinations among women with suspected early pregnancy failure. A minimum menstrual age for each was calculated, and pregnancy outcomes were assessed. The predictive value of the minimum menstrual age for the pregnancy outcome was assessed at both 42 and 49 days and compared to that of dating by the last menstrual period and sonography. Among a study cohort of 338 patients, the average gestational age calculated by the last menstrual period was 53 days; by sonography, it was 50 days; and by the minimum menstrual age, it was 35 days (P < .01). All cases in which there was no sonographically detectable embryonic heartbeat above a minimum menstrual age of 42 days resulted in pregnancy failure. The minimum menstrual age is a conservative estimate of the gestational age, with an estimated positive predictive value of 100% for early pregnancy failure when no embryonic heartbeat is seen after 42 days. The minimum menstrual age can be combined with other existing diagnostic clues to predict early pregnancy failure with greater accuracy.