Maturational sequence of fetal breathing movements

The inspiratory times of fetal breathing movements were measured in REM and NREM periods, respectively, and their changes with advancing gestational age were investigated. Ten women without complications in their 20th to 40th week of pregnancy were examined. Fetal breathing movements and REM were observed simultaneously using ultrasonography. REM and NREM periods were selected for analyzing breathing movements separate from the whole examination period. The inspiratory times of fetal breathing movements were measured with the hand-held pressure transducer. The changes in inspiratory time with fetal age showed the same pattern both in REM and NREM periods. There were no significant changes in inspiratory time before 28 weeks gestational age. After that, the inspiratory time lengthened, showing the maximum at 32-35 weeks and then shortened at 36-40 weeks gestational age. There were no differences of the inspiratory time between REM and NREM periods before 32 weeks. After 32 weeks, the inspiratory time in the NREM period was longer than in the REM period. These changes in fetal breathing movements are thought to be caused by the morphological maturation of the fetal lung and the functional development of respiratory and sleep center of the fetal central nervous system.