This study establishes reference intervals for embryo and fetal heart rates between 6 and 14 weeks of pregnancy based on crown-rump length, which may aid in evaluating early pregnancy viability.
May inform CRL-based fetal HR references for viability assessment; hypothesis-generating and requires prospective validation before clinical use.
OBJECTIVE: To determine reference intervals for the embryos/fetuses heart rate (HR) between 6 and 14 weeks of pregnancy. METHODS: A retrospective cross-sectional study was carried in a single center with singleton pregnancies of embryos/fetuses with a crown-rump length (CRL) between 5 and 85 mm. The HR was assessed by real time M-mode or spectrum Doppler ultrasound. To evaluate the correlation between embryo/fetal HR and CRL, polynomial equations were calculated, with adjustment by the determination coefficient (R(2)). RESULTS: A total of 5867 pregnancies were assessed. The mean gestational age was 10.37 ± 2.12 weeks. The mean maternal age was 26.41 ± 6.78 years. The mean embryo/fetal HR (bpm) for the CRL (mm) intervals 5├15; 15├25; 25├35; 35├45; 45├55; 55├65; 65├75; 75├85 was 145.1 ± 18.7; 167.2 ± 10.1; 166.9 ± 8.7; 165.5 ± 6.9; 162.2 ± 6.8; 159.2 ± 6.4; 157.1 ± 6.4; 154.9 ± 7.3; respectively. The following third-order equation best represented the correlation between embryo/fetal HR and CRL: HR = 119.25 + 3.596*CRL-0.07954*CRL(2 )+ 0.00051*CRL(3) (R(2 )= 0.36). CONCLUSION: Reference intervals of HR in embryos/fetuses in a large sample were determined. These reference intervals can be used in high-risk early pregnancy losses.
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Júnior et al. (2013) studied this question.
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