Evaluation of the embryonic and foetal heart rate at 6+0 to 11+6 weeks of gestation

Abstract

Objective: To establish the normal range of embryonic heart rate (EHR) and foetal heart rate (FHR) at 6+0 to 11+6 weeks of gestation, to evaluate the risk of pregnancy loss depending on EHR and FHR values and to establish if checking of FHR with the use of M-mode method is possible in different levels obstetric departments. Material and methods: Transvaginal or transabdominal ultrasound using M-mode in 255 singleton pregnancies. Maternal age varied between 16 and 44 years (mean 29}5 years). There were 67% primigravidas. Gestational week was established on the basis of CRL measurements. Demographic factors, obstetrical history and follow-up were collected. Data was statistically reviewed. Results: FHR varied between 47 and 192bpm (mean 154}26bpm). At 6 weeks, mean EHR was 116}21bpm, then slowly increased, reaching mean 172}9bpm at 10 weeks. At 11 weeks the mean FHR achieved the level of 165}7bpm. The difference was statistically significant. The r-correlation ratio between FHR and the gestational week was 0.58. In case of 7 embryos (2.75%) at 6,1 to 8,1 weeks of gestation slow FHR was noted (<100bpm). The scan performed 7-10 days later revealed miscarriages in all cases. Conclusions: EHR and FHR in the first trimester depends on gestational week. It increases since 6 to 9 weeks and decreases after 10 weeks. The highest values of FHR are observed between 9 and 10 weeks of gestation. The risk of early pregnancy loss increases significantly in case of detecting slow FHR. FHR can be checked by M-mode methods using any kind of ultrasound machine.