Reference intervals for first trimester embryonic/fetal heart rate in a Thai population

Area of Science:

• Obstetrics and Gynecology
• Fetal Medicine
• Diagnostic Ultrasound

Background:

• First-trimester embryonic/fetal heart rate is a key indicator of early pregnancy development.
• Establishing population-specific reference intervals is essential for accurate clinical interpretation.
• Previous studies may not fully represent diverse ethnic populations.

Purpose of the Study:

• To determine reference intervals for embryonic/fetal heart rate during the first trimester in a Thai population.
• To correlate embryonic/fetal heart rate with gestational age (GA) and crown-rump length (CRL).

Main Methods:

• A prospective descriptive cross-sectional study involving 547 normal pregnant women in their first trimester.
• Gestational age was determined by crown-rump length (CRL) using transvaginal ultrasound.
• Embryonic/fetal heart rate was measured using a 5 MHz vaginal probe and duplex color Doppler.

Main Results:

• Median embryonic/fetal heart rate increased from 124 bpm (GA 40-44 days) to 177 bpm (GA 60-64 days), then decreased to 159 bpm (GA 95-99 days).
• Regression analysis yielded equations correlating heart rate with GA (R=0.5) and CRL (R=0.58).
• Similar trends were observed when correlating heart rate with CRL, increasing from 131 bpm (CRL 5-9 mm) to 177 bpm (CRL 20-34 mm).

Conclusions:

• Reference intervals for first-trimester embryonic/fetal heart rate in the Thai population were successfully established.
• These established intervals can aid in the prediction of spontaneous abortion or chromosomal disorders.
• The findings support the use of ultrasound-derived heart rate data for risk assessment in early pregnancy.