Correlation between fetal heart rate, crown-rump length, and beta-human chorionic gonadotropin levels during the first trimester of well-timed conceptions resulting from infertility treatment.

Objectives: To evaluate sequential changes in fetal heart rate (FHR) during the first trimester of well-timed pregnancies resulting from infertility treatment and to correlate the data with fetal growth curve and beta-hCG levels.
Design: Serial measurements of FHR, crown-rump length (CRL) and beta-hCG at weekly intervals throughout the first trimester in 67 consecutive conceptions, resulting from infertility treatment. The day of preovulatory LH surge or of exogenous hCG administration was known in each case.
Setting: Hospital based and private assisted reproductive technology centers.
Results: Mean FHR was 108 +/- 12, 26 to 30 days after LH/hCG (5 weeks, 4 days from last menstrual period [LMP]) in embryos 3 +/- 0.3 mm in size; the FHR gradually increased, reaching a peak of 177 +/- 10 on days 51 to 55 (9 weeks from LMP) in embryos of 23 +/- 5.5 mm; it decreased to 156 +/- 5 on days 76 to 80 (12 weeks, 5 days from LMP) in embryos of 62 +/- 5.7 mm. There was, previously not reported, high level correlation between beta-hCG and FHR during the entire first trimester and positive correlation between FHR and CRL during the first 55 days from conception.
Conclusions: During the first trimester of pregnancy, FHR closely follows beta-hCG pattern. Correlation between beta-hCG and FHR is an interesting phenomenon that needs further investigation.