Troubled waters

Sterile amniotic fluid is important for your unborn baby's health, but it can become infected

What is amniotic fluid?
Amniotic fluid is usually sterile, and contained in the sac that surrounds your baby throughout pregnancy. It helps to protect and cushion, and also plays an important part in developing many of your baby's vital internal organs, such as 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 as a contribution from your baby's lungs and kidneys - it is continually taken up by your baby's swallowing, and is also sent across the afterbirth (placenta) into your own circulation.

Occasionally, it can become infected, and the condition is called intra-amniotic infection or acute chorioamnionitis (AC).

Intra-amniotic infection/acute chorioamnionitis (AC)
This is a general term for infection - by bacteria of various types - of the amniotic fluid and membranes/sac (the placenta and sometimes the umbilical cord can also be involved) and is the most common cause of premature (pre-term) labour. This is because the infection weakens the membranes, resulting in their premature rupture.

The condition is said to occur clinically - where it can be demonstrated in some form - in between one to five births in every 200. Sometimes, there may even be a 'silent' amniotic fluid infection, where the mother-to-be has no evident symptoms. This may well explain some of the apparently 'unexplainable' causes for early losses of the developing pregnancy - in the form of a miscarriage.

Sometimes infection can affect the area of the attachment of the placenta and this will result in a reduced blood flow between the mother and her baby. This will affect the oxygen supply to, and the clearance of waste from, the baby, causing 'foetal distress' - a term so often heard during pre-delivery checks - and, once again, may precipitate premature labour.

Other risks

  • Babies born prematurely as the result of AC are often ill because their lungs and other internal organs are immature; there may be a 'neonatal respiratory distress syndrome.'
  • There may be a septicaemia (blood poisoning) evident in babies who have been exposed to AC.
  • The bacteria themselves may also make the baby ill, of course, and pneumonia in the newborn is nearly always caused by an AC.
  • Chorioamnionitis may well cause the mother to have an excessive amount of bacteria in her own blood - this, too, may lead to a premature labour and infection of her newborn infant.
What causes infection?
There are some known risk factors, all of which affect the normal, protective mechanisms of either the birth canal or the urinary tract. These include:
  • Prolonged rupture of the membranes. This is the highest risk factor, but even in some prolonged labours infection may be seen and demonstrated. The risk of infection in the newborn increases as the duration of the ruptured membranes lengthens.
  • Multiple vaginal examination during labour.
  • Various types of internal monitoring systems used before or during labour.
The bacteria usually responsible for the infection are those that are normally present in the vagina, and it is disturbance of these, by various means, that causes the initial infection.

Signs and symptoms
The suspicions of a health care worker are aroused when there is some unexplained - i.e. no other source than from the womb - temperature rise in the mother-to-be, but it has been found that only some 8 to 25 mothers out of 100 with AC will have symptoms such as a fever, chills, etc. However, there may be some associated findings to suggest AC. These are:

  • An increased heart rate in the mother; more than 120 beats a minute is frequent and quite significant.
  • An increased foetal heart rate, which is less significant.
  • Abdominal (tummy) tenderness - when demonstrated to be the womb.
  • Foul-smelling liquor (amniotic fluid) or vaginal discharge.

Investigations and diagnosis
If infection is suspected, it will be necessary to:

  • Perform blood tests on the mother.
  • Possibly take a small sample of amniotic fluid, as in an amniocentesis, for cultures to demonstrate the presence of, and to identify, any bacteria.
  • Urine sample tests may be helpful.
  • A vaginal swab test may also be necessary to identify bacteria/germs.
A diagnosis can also be aided by the elimination of other possible conditions in the mother, which themselves can cause similar signs or symptoms. These will include severe kidney infections, respiratory/lung infections such as pneumonia, and infections within the abdominal cavity - especially appendicitis.

Complications

  • Initiation of premature/pre-term labour with premature rupture of the membranes (and subsequent premature/pre-term birth) with an increased risk of this at the earlier gestational ages.
  • Neonatal (within the first weeks of birth) infection in the baby. There is, unfortunately, a mortality rate of some 5 to 25 per cent.
  • Maternal infection is very common.
  • Post-partum haemorrhage (severe bleeding from the womb after delivery).
  • Difficult labour.
Treatment
  • With an early diagnosis antibiotics can certainly improve the developing situation, especially with regard to the baby.
  • There would not be an operative approach - in the form of Caesarean section - as possible complications in the presence of infection are likely.
  • Premature labour - as a result of infection - would be dealt with as in all other cases of early births.