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Abstract
Objective: The purpose of this study was to determine whether fetal heart rate (FHR) can be used to date pregnancies in the early first trimester using the gold standard of crown-rump length (CRL) dating as a reference.
Methods: This single center study evaluated women undergoing obstetrical ultrasounds between 4.5 and 8.5 weeks. FHR and gestational age (GA) based on CRL were obtained. Linear regression analysis and a Bland–Altman plot were used to demonstrate the relationship between the two measurements. A further simplified version of the relationship between CRL and FHR that may be clinically useful was calculated.
Results: 176 patients were included in the study. The Pearson correlation coefficient was 0.95, indicating a strong correlation between the two dating methods. The Bland–Altman plot demonstrated agreement across GA tested. A simple arithmetic formula of GA(weeks) = FHR (beats per minute)/20 was calculated. 169/176 patients had <4 days discrepancy between FHR- and CRL-based dating using this formula.
Conclusion: We found that a simple formula based on FHR may accurately date early pregnancies. This method, if further validated, may represent an important tool for pregnancy dating.
Declaration of interest
The authors report no declarations of interest.