This rate of demise was significantly higher than that of 7.2% (28 of 390) in pregnancies with a normal heart rate at 6.0-7.0 weeks and a normal heart rate by 8.0 weeks (P <.001, Fisher exact test). There were 59 pregnancies with a slow heart rate at 6.0-7.0 weeks and a normal heart rate at follow-up US by 8.0 weeks 15 (25.4%) resulted in first-trimester demise. The rates of first-trimester demise were 60.6% for pregnancies with slow heart rates at 6.0-7.0 weeks (188 of 310), 17.4% for those with borderline heart rates (103 of 593), and 9.1% for those with normal heart rates (186 of 2034). The Fisher exact test was used for all statistical comparisons. Pregnancies were excluded from the analysis if they were lost to follow-up before the end of first trimester. The heart rate was classified as slow if it was fewer than 90 beats per minute prior to 6.3 weeks or fewer than 110 beats/min at 6.3-7.0 weeks, normal if it was 100 or more beats/min at less than 6.3 weeks or 120 or more beats/min at 6.3-7.0 weeks, or borderline if it was 90-99 beats/min prior to 6.3 weeks or 110-119 beats/min at 6.3-7.0 weeks. Singleton pregnancies with an embryonic heart rate measured on a 6.0-7.0-week US scan were identified. The study was Health Insurance Portability and Accountability Act compliant. Institutional review board approval was granted informed consent was not required.

To determine retrospectively the outcome of pregnancies in which the embryo has a slow heart rate at 6.0-7.0 weeks gestation and a normal heart rate at follow-up ultrasonography (US) by 8.0 weeks gestation.

Normal heart rate at 6 weeks