Embryonal heart rate as a predictor of pregnancy outcome: a prospective analysis.

To evaluate the association between embryonal heart rate and pregnancy outcome, we prospectively followed 50 very early pregnancies (4.5 to 7.3 weeks of gestation) through the first trimester. Of the 11 embryos that miscarried, 6 had initial heart rates below 85 beats per minute (bpm); in contrast, none of the viable embryos had initial heart rates of or below 85 bpm (P less than 0.0001). A rise in mean heart rate was seen among the viable embryos with increasing gestational age, in concordance with previously reported rates.