The onset of labour before the 37th week of pregnancy
The normal duration of pregnancy is about 40 weeks. Labour that starts before 37 weeks is considered premature. Premature labour involves few extra risks for the mother, but premature babies often have problems because of their small size and immaturity (see Problems of the premature baby).
If premature labour is diagnosed early, there is a chance that it can be stopped and that the pregnancy will continue. If labour cannot be stopped completely, it may be delayed for a day or two so that corticosteroids can be given to help the fetus to mature. Premature labour occurs in approximately 1 in every 10 births and is more common in very young mothers and those who are over the age of 35.
Often, the cause of premature labour is not known, but triggering factors can sometimes be identified.
A multiple pregnancy often results in premature labour, possibly because the uterus is stretched (see Multiple pregnancy and its problems). An excessive amount of fluid around the fetus (see Polyhydramnios) has the same effect.
Factors that increase the risk of premature labour include smoking and alcohol or drug abuse during pregnancy, heavy work, stress, a previous premature labour, and long-term disorders such as diabetes mellitus.
The symptoms of premature labour may be mistaken initially for the backache and painless contractions that commonly occur in late pregnancy. They include:
Intermittent pain in the lower back.
Tightening felt in the abdomen that become regular painful contractions.
A discharge of blood and mucus from the vagina.
If you think you are going into premature labour, you should contact your doctor or midwife immediately. The earlier premature labour is diagnosed, the greater the chances of stopping it. You may be admitted to hospital and transferred to a centre with a special care baby unit in case it is impossible to stop labour and you deliver your baby early.
You will be examined to make sure that you are in labour and to assess how far it has advanced. The uterine contractions and the heartbeat of the fetus will be monitored regularly (see Fetal monitoring). Tests may also be carried out to try to find the cause of the premature labour.
If the fetus is not mature enough to be delivered safely, your doctor may try to stop labour by giving you an intravenous infusion of drugs (see Drugs for labour) that sometimes stop the muscles of the uterus from contracting. You should rest completely during treatment because movement encourages uterine contractions. Your doctor may also prescribe antibiotics to reduce any risk of infection in the fetus.
If your labour cannot be stopped, the doctor may try to postpone it for a couple of days so that you can be given two injections of corticosteroid drugs, which help the lungs of the fetus to mature. This procedure reduces the risk of breathing problems in the baby after delivery. The fetus will be monitored for signs of fetal distress. In many cases, a carefully monitored vaginal delivery is possible, but, if there are risk factors such as a multiple pregnancy, it may be necessary to carry out a caesarean section.
In many cases, labour can be stopped and the pregnancy then progresses to about 40 weeks. Otherwise, postponing labour for a day or two allows time for corticosteroid drug treatment to improve the fetus’s chance of survival. Babies born before 37 weeks may need to be cared for and monitored in a special care baby unit until they are more mature. Premature labour often recurs in subsequent pregnancies.
From the 2010 revision of the Complete Home Medical Guide © Dorling Kindersley Limited.