An excessive amount of amniotic fluid surrounding the fetus in the uterus
- Genetics as a risk factor depends on the cause
- Age and lifestyle are not significant factors
Normally, the amount of amniotic fluid surrounding the fetus does not exceed 1.5 litres (3 pints). In polyhydramnios, more than 2 litres (4 pints) of amniotic fluid build up, causing abdominal discomfort or pain in the mother.
Excess fluid makes it easier for the fetus to move around in the uterus. For this reason, the fetus may not lie in the normal head-down position at the end of pregnancy (see Abnormal presentation). Excessive amounts of fluid also increase the likelihood of a premature labour or of premature rupture of membranes.
What are the types?
There are two types of polyhydramnios: chronic, in which the amniotic fluid accumulates slowly over several weeks; and acute, in which the amniotic fluid accumulates over a few days.
Chronic polyhydramnios is the more common form. It develops from about week 32 of pregnancy and causes gradually worsening abdominal discomfort. Breathing difficulties, indigestion, and retention of fluid also sometimes occur. In many women, no cause is found for chronic polyhydramnios. However, the condition occurs more often in mothers who have pre-existing diabetes mellitus and in women carrying more than one fetus (see Multiple pregnancy and its problems).
The acute form of polyhydramnios develops from 22 weeks and is typically associated with an identical twin pregnancy. It is also more likely if the fetus has a developmental defect, such as spina bifida (see Neural tube defects). The symptoms are similar to but more severe than those of chronic polyhydramnios. Frequently, there is severe abdominal pain, nausea, and vomiting.
What might be done?
Your doctor may suspect that you have polyhydramnios if your abdomen is larger than would be expected for the stage of your pregnancy. You will probably undergo ultrasound scanning (see Ultrasound scanning in pregnancy) to confirm the diagnosis and to look for fetal abnormalities. You may also need a blood test to check whether you have diabetes mellitus.
Usually, chronic cases can be treated by bed rest. If troublesome symptoms occur late in pregnancy, induction of labour may be recommended.
If you have acute polyhydramnios, your doctor may recommend induction of labour if the fetus or fetuses are mature enough. If the fetus is immature, you may be given corticosteroid injections to help the lungs of the fetus mature so that it can be delivered early. Abdominal pain may be relieved temporarily by removing some of the amniotic fluid from the uterus using a needle inserted into the abdomen. If required, the procedure can be repeated.
If you have diabetes mellitus, polyhydramnios may recur in subsequent pregnancies. However, careful control of your diabetes should reduce this risk. If you have polyhydramnios due to other causes, you are not at increased risk in future pregnancies.
From the 2010 revision of the Complete Home Medical Guide © Dorling Kindersley Limited.