VERY EARLY (24-56 DAYS FROM LAST MENSTRUAL PERIOD) EMBRYONIC HEART-RATE IN NORMAL PREGNANCIES

To determine embryonic heart rate in early gestations, 426 ultrasonogr aphic examinations from 24 to 56 days from onset of last menstrual per iod (LMP) were studied. All pregnancies had a subsequent successful ou tcome. 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 f rom 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 cardi ac activity. By day 37 from onset of LMP all pregnancies demonstrated embryonic cardiac activity. From days 34 to 56, mean embryonic heart r ate 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 i n normal pregnancies.