Long-term prognosis of pregnancies complicated by slow embryonic heart rates in the early first trimester

Slow embryonic heart rates at gestational age 7 weeks or less are associate d with high risk of first trimester death. Our goal was to determine the pr ognosis for those embryos with slow early heart rates who survive the first trimester. We prospectively recorded embryonic heart rates for all obstetr ical sonograms obtained on singleton pregnancies at or before 7.0 weeks' ge station since 1993. We collected information about pregnancy outcome, inclu ding date of live birth or in utero death and presence and nature of congen ital anomalies. First trimester survival rate was 61.6% among 531 embryos w ith slow early heart rates (<100 bpm at less than or equal to 6.2 weeks, <1 20 bpm at 6.3 to 7.0 weeks), lower than the survival rate of 91.5% among 15 01 embryos with normal heart rates (p < 10(-8), Fisher's exact test). Among 299 pregnancies in which the early heart rate was slow and the fetus was s till alive at the end of the first trimester, 277 (92.6%) resulted in liveb orn infants without congenital anomalies, similar to the frequency of 95.1% in cases with normal early heart rates (p > 0.10, Fisher's exact test). St ructural and chromosomal anomalies, however, occurred more than twice as fr equently in cases with slow early heart rates: 5.4% (16 of 299) of the firs t trimester survivors with slow early heart rates proved to have anomalies, as compared to 2.4% (31 of 1281) of cases with normal early heart rates (p < 0.05, Fisher's exact test). In conclusion, a pregnancy in which the embr yo has a slow heart rate at or before 7.0 weeks' gestation and which contin ues beyond the first trimester has a high likelihood (>90%) of resulting in a Liveborn neonate without congenital anomalies. Embryos with slow early h eart rates do, however, have a greater risk of having anomalies than embryo s with normal early heart rates.