Duration of biophysical profile in periviable and very preterm low-risk pregnancies

Abstract

BackgroundIn recent years, perinatal viability has shifted from 24 to 22 weeks of gestation at many institutions after improvements in survival in neonates delivered at the limit of viability. Monitoring these fetuses is essential since antenatal interventions with resuscitation efforts are available for patients at risk of delivery at the limit of viability. However, fetal monitoring as biophysical profile has not been extensively studied in very preterm pregnancies, particularly in the periviable period (20 weeks 0 days – 23 weeks 6 days). Objectives (i)To investigate whether the completion of biophysical profiles within 30 min is feasible in very preterm pregnancies. (ii) To determine the average observation time required to achieve a score of 8/8 in very preterm pregnancies from 20 weeks 0 days to 31 weeks 6 days. Study DesignThis study prospectively evaluated biophysical scores in singleton pregnancies undergoing routine ultrasonography at or near viability from 20 weeks 0 days to 23 weeks 6 days (periviable or group I), 24 weeks 0 days to 27 weeks 6 days (group II), and 28 weeks 0 days to 31 weeks 6 days (group III). The results and duration of biophysical profiles were compared to those of a control group (32 weeks 0 days to 35 weeks 6 days) undergoing indicated fetal surveillance. Biophysical profiles were performed on all studied pregnancies until a score of 8/8 was obtained. When more than one biophysical profile was obtained during pregnancy, each was analyzed individually. Pregnancies with fetal anomalies or obstetric/medical indications for fetal well-being surveillance were excluded. Analysis of variance and post-hoc Tukey’s test were used for comparisons. ResultsData was completed for 123 participants, yielding 79, 75, and 72 studies for groups I, II, and III, respectively. The control group included 42 patients, yielding 140 studies. At 30 min, 80% (63/79) of the studies in the periviable group had a score of 8/8, compared to 100% (140/140) in the control group (P<0.001). The mean + standard deviation time in minutes to achieve a biophysical score of 8/8 was 23.3 + 10.1 in the periviable group compared to 9.4 + 6.5 in controls (P<0.001). Extending the study to +2 standard deviations (43.6 min) in the periviable group resulted in 97% (77/79) of the scans scoring 8/8 in the absence of adverse outcomes. In the other groups, a biophysical score of 8/8 within 30 min was obtained in 97% (73/75) and 100% (72/72) in groups II and III, respectively; the mean + standard deviation times were 17.1 + 8.4 min (group II) and 13.1 + 7.3 min (group III). No adverse outcomes developed during the study participation in groups I–III. ConclusionsBiophysical scores of 8/8 can be successfully obtained in low-risk periviable pregnancies (20 weeks 0 days – 23 weeks 6 days) within an observation time longer than the standard 30 min. The time required to reach a score of 8/8 decreases as gestation progresses. We suggest adjusting the observation time for biophysical profile completion according to the gestational age.