The fetus receives all the food he needs through the placenta from this mother's blood. One of the signs that the placenta is not working well is a fetus that is growing slowly. This slow growth may be found by feeling the size of the uterus or by ultrasound examination. From minute to minute, the fetus also needs a vital supply of oxygen from the mother. If he did not get that oxygen he would soon die. Much of the care of the baby during the modern management of labour is devoted to a careful watch of his oxygen supply. Usually the baby's heart beats 120 and 140 times a minute, but it may get faster or slower if he is short of oxygen. Nurses are therefore trained to listen to the baby's heart rate frequently as labour progresses; if she hears a change she will tell the doctor. This is very satisfactory for the ordinary management of labour, but if the doctors feel there is a very high risk of the baby losing his oxygen supply, such as the baby who has stopped growing, a more sophisticated method of watching the baby is needed. It is now possible to record heart rate and contraction of the uterus by special devices which are readily available at most birthing clinics. A very fast heart-rate or marked slowing of the rate during or just after a contraction are both signs that the baby may have very little oxygen and needs immediate delivery. In addition a small blood sample can be taken from the head of the baby; the baby scalp is prickled and a few drops of blood are allowed to run into a tube. The blood can be analyzed to see if it is acid, very acid blood is produced when the baby lacks oxygen.

These new methods mean that there is more machinery around the mother in the labour ward, but it enables the doctors to keep a close eye on the baby and deliver him quickly if necessary.