A fetus in the womb does not breathe through the mouth or nose, it is supplied with nutrients and oxygen through the placenta and umbilical cord.
The fetus lives in amniotic fluid in the uterine cavity, which is devoid of gas, and the fetus’ lungs and trachea are filled with amniotic fluid-like substances, so there is no way for it to breathe through the mouth and nose. The nutrients and oxygen needed for fetal growth and development are obtained from the mother mainly through the placenta and umbilical cord.
If the fetus is deprived of oxygen in the late stages of pregnancy and at the time of delivery, it may stimulate respiratory movements, which may result in excessive aspiration of amniotic fluid, wet lungs or even lung infections in the newborn.
After delivery, with the first cry of the newborn, the alveoli expand and breathe on their own, and the airways of the newborn are opened to form a normal respiratory system.