Embryonic heart activity: appearance and development in early human pregnancy.

The appearance and development of embryonic cardiac activity was studied in early human pregnancies established by in-vitro fertilization (IVF) using transvaginal sonography. Embryonic cardiac activity could be detected as early as 25 days after follicle aspiration. The range in appearance of embryonic cardiac activity in normal continuing pregnancies was 5 days. There was no correlation with maternal age, day of embryo transfer, or cell stage at embryo transfer. As the difference in appearance of embryonic cardiac activity was associated with a difference in crown-rump length whilst the subsequent growth curve was normal we ascribe these findings to different duration of the implantation stage. The later cardiac activity was detected the greater the risk of miscarriage. Reference curves were created relating embryonic heart rate to the number of days after follicle aspiration, the number of days that cardiac activity is present and the crown-rump length. In pregnancies ending in miscarriage heart rate patterns fell away from the reference curve. Embryonic factors seem to play an essential role in these observations.