[Fetal respiratory movements].

In the human species, foetal breathing movements are detectable from the fifteenth week of gestation and their incidence increases until the start of the third trimester. Over the last 10 weeks, breathing movements are present for 30% of the time. These are contemporaneous with body and ocular movements, suggesting an association between breathing movements and paradoxical sleep, as has been seen in the foetal lamb. These phases of activity alternate with phases of foetal immobility during which breathing movements are often absent. The incidence of foetal movements rises in the late post-prandial period, under the effect of maternal hyperglycaemia. After the establishment of regular uterine contractions, foetal breathing movements disappear, perhaps under the effect of prostaglandins E2 and/or a reduction in placental blood flow. Maternal hypercapnia leads to a rise in foetal breathing movements, which corresponds in the animal to the paradoxical sleep state. In the foetal lamb, hypoxaemia is accompanied by a cessation of breathing movements coinciding with a passage to quiet sleep. It is probable that the human foetus produces a similar reaction to hypoxaemia. During quiet sleep an inhibition of the respiratory centres would exist, disappearing during paradoxical sleep. Alcohol and certain anaesthetic agents lead to an inhibition of foetal breathing movements. The effect of tobacco remains controversial. The role of foetal breathing movements in pulmonary maturation is discussed in the human species.