Fetal breathing movements (FBM) are episodic rhythmic contractions of the diaphragm and other muscles of respiration.
Fetal breathing may be noticed as early as 15 weeks of gestation. At 24 -28 weeks, the fetus breaths about 10-20% of the time, increasing to 30% at 30 weeks of pregnancy 1. Fetal breathing is crucial to the development of the lungs 2. Fetal respiratory rate may vary from 30 -70 breaths per minute with periods of apnea up to 2 hours in between 3,4.
Factors affecting fetal breathing movements
smoking, alcohol, narcotics, IUGR: decrease fetal breathing 2
caffeine, amphetamine: increase fetal breathing 4
Radiographic features
Ultrasound
Ultrasound is the best modality to look for fetal breathing movements. Fetal breathing movements are best visualized in the sagittal plane as the episodic rhythmic downward movements of the diaphragm. It is important to differentiate fetal breathing from maternal respiratory movements, which involve the complete movement of the entire sonographic frame.
Fetal respiratory movements form one of five parameters of the fetal biophysical profile used to assess antenatal fetal wellbeing. At least one breathing episode lasting ≥30 seconds during 30 minutes of observation is considered normal breathing.
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