Very early (24-56 days from last menstrual period) embryonic heart rate in normal pregnancies.

S Britten
D M Soenksen
M Bustillo
C B Coulam


To determine embryonic heart rate in early gestations, 426 ultrasonographic examinations from 24 to 56 days from onset of last menstrual period (LMP) were studied. All pregnancies had a subsequent successful outcome. Transvaginal ultrasonography was performed using an Acuson 128 10XP with a 5 MHz probe. Embryonic heart rate was determined by M-mode. No embryonic heart rate was observed prior to 34 days of gestation from onset of LMP (n = 65). At 35 days, two of 13 (15%) pregnancies had cardiac activity, and by 36 days 16 of 19 (82%) pregnancies had cardiac activity. By day 37 from onset of LMP all pregnancies demonstrated embryonic cardiac activity. From days 34 to 56, mean embryonic heart rate rose from 94 to 166 beats/min. We conclude that embryonic cardiac activity is first apparent at day 34 and should be visible by day 37 in normal pregnancies.