Too much of a good thing

Some conditions of the unborn baby or pregnancy can give rise to excess amniotic fluid, says Dr Howard Lee

What is amniotic fluid?
Amniotic fluid is usually sterile, and contained in the sac that surrounds a baby throughout pregnancy. It helps to protect and cushion, and also plays an important part in developing many of the baby's vital internal organs - like the lungs, kidneys and gut.

The normal amount may vary, but there's usually a slow increase until about 36 weeks of pregnancy - then a slow decrease. Most women carry about 500 ml of amniotic fluid. The fluid is produced by the inner lining of the sac (amnion) as well from the baby's lungs and kidneys - it is continually taken up by the baby's swallowing, and is also sent across the afterbirth (placenta) into the mother's circulation.

The commonest problems with amniotic fluid - which occur in about seven out of every 100 pregnancies - usually take the form of either too much fluid (hydramnios or polyhydramnios) or too little fluid (oligohydramnios). Both conditions are associated with abnormalities in the baby's development or some other pregnancy complication. Any abnormal difference in the amounts of the amniotic fluid may be either the cause or the result of a problem within a pregnancy.

Hydramnios
This is the condition, occurring in about three to four pregnancies in every 100, where there is too much fluid around the baby. A minor to moderate degree of fluid increase (two to three litres) is quite common and, if this increase develops in the second trimester (three month period), there is a good chance that your baby is fine and that the fluid increase will disappear on its own.

Hydramnios is a symptom of health problems, rather than the cause. Remember, too, that hydramnios may also occur during perfectly healthy multiple pregnancies.

Causes
Either too much fluid is being produced, or there is a problem with the fluid being taken up, or both. The factors associated with hydramnios include:

Maternal

  • Diabetes
Baby (foetal)
  • Gastrointestinal (gut) abnormalities that block the passage of fluid
  • Abnormal swallowing due to brain or chromosomal abnormalities
  • Cleft lip and/or palate
  • Twin-to-twin transfusion syndrome
  • Congenital (acquired in pregnancy) infection
  • Heart failure
Problems
  • Overstretching of the womb (uterus) may lead to premature/pre-term labour or premature rupture of the membranes (amniotic sac).
  • Large amounts of fluid leaving the womb, at rupture of the sac, may increase the risk of a too early detachment of the afterbirth - placental abruption - that will compromise the baby's circulation. The umbilical cord may also fall down through the cervix opening - umbilical cord prolapse - where it may become compressed, preventing a continuing circulation of oxygen to the baby.
Signs and symptoms
Often mild hydramnios has no symptoms, but each mother may experience any symptoms differently, and if you have any breathlessness, abdominal pain, marked swelling or bloating - which can all be recognisable features of more severe hydramnios - it is important that you let your health professionals know, just in case. The most common features are:
  • Rapid growth of the womb (uterus)
  • Discomfort in the belly (abdomen)
  • Uterine contractions
All of these may, of course, resemble other medical conditions, so always speak with your own doctor so that a proper diagnosis can be made.

How is the diagnosis made?
It will usually be necessary to take a full medical history, and make a proper examination, following which an ultrasound examination will be made. This will measure pockets of fluid - called the Amniotic Fluid Index - in order to estimate the total volume. These indices do change depending on gestational age, therefore the norms for your baby's age will need to be known.

At the same time, this ultrasound examination may help to find a possible cause of the hydramnios - such as a multiple pregnancy, or some form of birth defect.

Treatment
Sometimes it can only be the symptoms of hydramnios that can be treated and not the cause. Your obstetrician will determine any specific treatments. These will be based on:

  • Your pregnancy
  • Your overall health and medical history
  • The extent of the condition
  • Your own tolerance for specific treatments, procedures and medications
  • Expectations for the course of the condition
  • Your own opinion or preferences
All that may be necessary is:
  • Close monitoring of the amount of amniotic fluid - repeat measures of the AF Index - with frequent follow-up visits.
  • Medications to reduce the urine production of your baby.
  • Medications for the relief of 'inflammation', like Indomethacin.
  • Amniotic fluid reduction (amniocentesis), performed by withdrawing fluid through a small needle introduced into the sac via the tummy wall. This may need to be repeated on several occasions.
  • Delivery of your baby - if complications endanger the well-being of either your baby's or your own health.

The main aim of any treatment is to relieve any discomfort that may be present and to continue the pregnancy if this is possible. It is not possible to prevent hydramnios.