Fetal Heart Rate in the First Trimester of Pregnancy - Revista Brasileira de Ginecologia e Obstetrícia

Purpose: to determine normal ranges for fetal heart rate (FHR) between the 10th and 14th week of pregnancy. Methods: a total of 1078 fetuses within a crown-rump length (CRL) from the 10th to the 14th week of pregnancy were evaluated. The fetuses were divided into 4 groups: Group I (10 weeks), Group II (11 weeks), Group III (12 weeks), Group IV (13 weeks). The fetal heart was seen using B-mode/M-mode at a sagital plane and FHR was recorded. FHR was electronically calculated using calipers within 3 consecutive cycles without fetal moveiments. Results: FRH ranged from 136 to 178 bpm among the 1078 studied fetuses. Median values and standard deviations (5 and 95 percentiles) were calculated for each group. The FHR range for each group was: 158 to 184 bpm (Group I); 155 to 175 bpm (Group II); 152 to 172 bpm (Group III) and 149 to 168 bpm (Group IV). Our main finding was a progressive reduction in FHR during the time period under consideration. Discussion: FHR evaluation in the first trimester of gestation is a simple procedure and should be analyzed not only qualitatively but also quantitatively. Published papers have shown a relation ship between FHR and fetal prognosis.