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.
Keywords: Crown rump length; early pregnancy dating; fetal heart rate dating.