Measurement of human fetal breathing movements in healthy pregnancies using a real-time scanner.

Real-time scanners have permitted investigators to measure fetal breathing movements during pregnancy in humans. It has been demonstrated that fetal breathing movements are episodic and occur about 30% of the time during the last 10 wk of pregnancy. Design of studies must account for the episodic nature of fetal breathing movements. It will be important to account for the relationship of fetal breathing movements to maternal meals, time of day, and gestational age of fetuses. Furthermore, cigarette smoking, alcohol, and drugs may alter fetal breathing measurements. Finally, fetal breathing movements are absent during accelerated labor and may normally be diminished during the last 3 days prior to spontaneous term labor. Measurement of fetal breathing movements using real-time scanners has helped to understand circadian rhythms in fetal life and may ultimately be of use in the assessment of fetal health. It is important that much more information be obtained concerning factors that normally influence fetal breathing movements before proper strategies can be suggested for the use of these measurements in the clinical assessment of fetal health.