Polyhydramnios or Excessive Amniotic Fluid

Polyhydramnios is the medical word for having an excessive amount of amniotic fluid in the womb. It is a rare condition occurring in only one percent of UK pregnancies. On the opposite end of the scale is the condition called oligohydramnios, which is having too little amniotic fluid present in the uterus.

Amniotic fluid

Your baby is surrounded by amniotic fluid which is encased in the amniotic sac within the uterine walls. This fluid protects and cushions the baby against any unwanted knocks or bumps to your tummy, as well as helping the baby's lungs to mature whilst protecting the baby against infections.

The amniotic fluid volume increases steadily throughout pregnancy reaching its peak at around 36 weeks. At this point there is approximately one litre of amniotic fluid present. As you progress to term and 40 weeks, the amount decreases to around 800ml. Babies in the womb regularly swallow the amniotic fluid and pass it out of their bodies as urine. The baby is therefore controlling the amount of amniotic fluid that exists around him or her. If this delicate balance is upset in any way, the volume of amniotic fluid may increase suddenly and quickly. In severe cases this might treble to around three litres of fluid.

Diagnosing polyhydramnios

Polyhydramnios is most likely to occur from the 30th week of pregnancy onwards. You may notice that your tummy is increasing in size too quickly and your skin is shiny and stretched looking. Climbing the stairs may become difficult as you develop the feeling of breathlessness. Other symptoms to watch out for are intense heartburn, constipation, abdominal pain, varicose veins and swollen legs.

The midwife or doctor will detect during an examination that you are large for your dates. It may be difficult for them to hear your baby's heartbeat or feel the baby as there is so much fluid around the baby. An ultrasound scan can confirm polyhydramnios. By measuring the fluid in four areas of the amniotic sac, the sonographer can work out your amniotic fluid index (AFI). You have polyhydramnios if your AFI is over 24cm. The greater the figure, the more severe the condition is.

Causes of polyhydramnios

It is difficult to ascertain the cause of polyhydramnios. In around 60 percent of cases there is no known reason as to why the condition has developed. Problems may arise from the baby, the mother or the placenta. Causes can include:

• Pregnancy with twins, particularly identical or monozygotic twins who share the same placenta.
• Diabetes, where blood sugar levels are out of control. As the baby's urine output goes up, this then increases the levels of amniotic fluid.
• Chromosomal abnormalities such as Edward's or Down's Syndrome.
• Congenital problems, such as a blocked oesophagus, or issues of the heart, kidneys or central nervous system.
• Infections which affect your baby, such as syphilis, rubella, toxoplasmosis and cytomegalovirus.
• Placenta developing a tumour or issues with the umbilical cord arteries.

While all of this sounds terrifying and leads to further questions, it is important to remember that most women diagnosed with polyhydramnios deliver healthy babies, especially if the diagnosis is mild.

Managing polyhydramnios

If you already are diagnosed with diabetes you will automatically be asked to take a glucose tolerance test to determine your blood glucose levels. If high, you will be referred to a specialist who can help you to reduce these blood sugar levels. This, in turn, should reduce the amount of amniotic fluid surrounding the baby.

Ultrasound scans should help in identifying any problems your baby may have. If nothing untoward is picked up on the scan then it is most likely that your baby is fine and that something else is the cause of the excess fluid.

You will be kept a close eye on for the last couple of months of pregnancy with regular antenatal check-ups. Depending on the cause of the polyhydramnios you may be given medication which reduces the baby's urine output.

In severe cases your specialist may decide to drain some of the fluid, reducing the volume. This should reduce the risk of the placenta coming away from the uterus wall or the onset of premature labour. This is a very fine calculation, however, as taking too much fluid out can actually increase the risk of the placenta separating from the uterus wall, as well as leading to such complications as bleeding and infection.

In most cases, you will be advised to rest as much as you can, which may mean starting maternity leave earlier than planned. As your uterus is so swollen, even with plenty of rest you may still go into premature labour. Your midwife will ensure that you know what signs to look out for so you can contact the hospital straight away if you start having contractions or your waters break.

Giving birth with polyhydramnios

Due to the large volume of fluid in the uterus along with the baby, around one in five women with this condition will give birth early as their womb simply cannot hold the heavy volume any longer. If you go into labour before 37 weeks it is essential you get to hospital as fast as possible. Ring for an ambulance if there is nobody who can take you and also ring the delivery suite to alert them of your arrival.

The team of midwives and doctors will carefully monitor you during labour. The excess fluid may make it hard for the baby to manoeuvre head down into the pelvic area. When your waters break, the umbilical cord can be swept down into the vagina before baby's head. If this were to happen you may need to have an emergency caesarean section. Also when the waters break, the amniotic fluid may rush out causing the placenta to shrink suddenly and come away from the uterus wall. After birth you have an increased risk of haemorrhaging.

You may be offered the option of an elective caesarean, especially if you are carrying twins, your baby is very large, or is lying crossways or is in an unsettled position.