It is possible to see a rhythmic movement on the abdomen that corresponds to fetal practice breathing, but this motion is often subtle and easily confused with other movements. The movements, known as Fetal Breathing Movements (FBMs), are a standard and necessary part of development, even though the baby is not taking in air. FBMs are a reassuring indicator of the baby’s health and preparation for life outside the womb.
The Biology of Fetal Breathing Movements
Fetal Breathing Movements (FBMs) are not true respiration, as the baby receives all necessary oxygen through the placenta and umbilical cord. FBMs are rhythmic contractions of the respiratory muscles that serve as practice for life after birth. The fetus moves amniotic fluid into and out of its lungs during these episodes, powered by the diaphragm and the chest wall muscles. These movements build strength and coordination for the moment the baby takes its first breath of air. FBMs are episodic and often alternate with periods of rest or deep sleep, which is a pattern distinct from the continuous breathing of an infant. Their presence is a sign that the fetal central nervous system is functioning correctly.
Visualizing Fetal Activity
FBMs are typically subtle, appearing as a faint, rhythmic pulsation or gentle ripple near the baby’s chest or diaphragm area. This motion is much smaller and quicker than a full kick or a body roll. It can be difficult to distinguish FBMs from other fetal activity, particularly the jerky, sustained movements of fetal hiccups; practice breathing is a smoother, more localized rise and fall of the abdomen. Visibility depends on the baby’s position, the amount of amniotic fluid present, and the mother’s body composition. While healthcare providers use ultrasound to visualize the downward movement of the diaphragm, some mothers in the third trimester report seeing a fast, consistent, localized rhythmic motion. However, this visible activity is not a consistently reliable sign for parents to monitor alone.
Developmental Role and Timing of Practice Breathing
Fetal Breathing Movements begin sporadically around 10 to 12 weeks of gestation. They become more organized around 20 to 22 weeks and increase in frequency in the third trimester, with the baby spending up to 30 to 40% of its time practicing in the final weeks. The purpose of FBMs is to prepare the lungs for their post-birth function. The mechanical stretching stimulates lung tissue growth, helps expand the air sacs (alveoli), and aids in the production and proper distribution of surfactant, which prevents the alveoli from collapsing. FBMs are routinely assessed during a biophysical profile, often performed in high-risk pregnancies. A healthy fetus must exhibit an episode lasting at least 30 seconds during a 30-minute observation window, as the movements are suppressed by factors like hypoxia or deep fetal sleep.