First trimester fetal heart rate measurements by transvaginal ultrasound combined with pulsed Doppler: an evaluation of 1331 cases

The aim of this study is to present the cardiac activity measurements obtained from 1331 embryos and first trimester fetuses in whom the crown-rump length (CRL) measurements were between 2 and 60 mm, and to correlate the pattern of changes according to growth in body length, with an objective and reliable technique; transvaginal ultrasound combined with pulsed Doppler. Sonographic examinations were performed using a Combison 320-Kretz scanner with a 5–7.5 MHz vaginal probe with 240° scanning angle, combined with a 4.5 MHz pulsed Doppler. As the embryo grows, the mean heart rate increases sharply, from 106.8 ± 6.4 at a CRL of 2 mm to 178.3 ± 7.0 at a CRL of 23 mm; followed by a plateau and a slight decline thereafter. Statistical analysis of the body length and corresponding heart rate revealed a relationship with a correlation coefficient of 0.61 (P < 0.01), whereas relationship between CRL ≤ 23 and corresponding heart rate was striking with a correlation coefficient of 0.87 (P < 0.01).