Comparison of the accuracy of gestational age estimation from fetal heart rate and crown-rump length

Abstract

Objective: To compare the accuracy of gestational age (GA) estimation predicted by fetal heart rate (FHR) versus crown-rump length (CRL) measurements in early pregnancies. Methods: A total of 145 infertile women with singleton intrauterine pregnancies conceived through in vitro fertilization underwent vaginal ultrasonographic examination in early stage of pregnancy. We performed 197 FHR and 398 CRL measurements. The relationship between GA (counted with the day of oocyte retrieval used as day 14) and the FHR or CRL was explored with regression analysis by means of least squares. Polynomials up to the third order were analyzed, and the coefficient of determination ( R 2) was calculated. Results: Fetal cardiac activity could be detected as early as 38 days, gradually increased to 188 beats per minute at 62 days of gestation. Regression analysis with GA as dependent variable resulted in R 2 values of 0.906, 0.907, and 0.908 for the first, second, and third order polynomials, respectively. The standard deviations around the regression line were 2.90, 2.81, and 2.84 days, respectively. The second order polynomial to describe GA (days) estimated by FHR (beats per min): GA = 3.02E-4∗FHR 2 + 1.60E-1∗FHR + 2.22E+1. On the other hand, the CRL was measured at 38 days to 62 days of gestation. Regression analysis resulted in R 2 values of 0.827, 0.839, and 0.841, respectively. The deviations were 4.11, 3.83, and 3.89 days, respectively. The second order polynomial to describe GA estimated by CRL (mm): GA = −2.10E-2∗CRL 2 + 1.49E+0∗CRL + 3.86E+1. There was no difference between the R 2 values and no difference between the standard deviations around the regression lines. Conclusion: Our results indicate no statistically significant difference in the accuracy of GA estimation predicted by FHR versus CRL measurements. But better mathematical fits were obtained when the data of FHR were used for GA estimation. These findings suggest that the FHR measurement may be a new method for early ultrasound dating. This study mentions for the first time the possibility of “FHR dating” with functional data.