Does diurnal rhythm have an impact on fetal biophysical profile?

To investigate whether parameters in fetal biophysical profile (BPP) testing exhibit a diurnal rhythm and to discuss the probable factors associated with these variables.Thirty healthy primigravid patients carrying pregnancies between 35 and 40 completed weeks were enrolled for the study. Fetal BPP testing was performed for each patient both in the early morning (08:00-10:00 am) and in the late evening (08:00-10:00 pm), and the scoring parameters were compared between morning and evening tests.BPP scores in the evening were significantly higher than that in the morning (p < 0.05). Deepest vertical amniotic pocket measurements and fetal breathing absence in the morning mostly contributed to this variation (p < 0.001). Fetal movement counts were also significantly lower in the morning tests (p < 0.001).The parameters of BPP exhibit circadian variations in healthy fetuses, which may be associated with many factors such as fetomaternal hormones. It is essential for the clinician to be aware of these changes when interpreting the results, as interventions based on false-positive results may have deleterious effects on both the mother and her fetus.