During pregnancy your baby is surrounded by a substance called amniotic fluid which helps protect both the baby and the uterus. It is this fluid which is referred to when people talk about waters breaking. It has many important functions but sometimes there can be problems. Read on to find out more about this amazing substance and what can be done if something goes wrong.
What is amniotic fluid?
Amniotic fluid is a colourless fluid that surrounds the baby in your uterus. It helps to protect and cushion your baby inside the amniotic sac and protects against infection to the baby and your uterus. Amniotic fluid also plays a vital role in the development of internal organs, such as the lungs and kidneys.
Where does it come from?
During the first trimester of your pregnancy the placenta, amniotic membranes and your own circulation produce fluid to fill the amniotic sac as your baby grows. At this stage, your baby will swallow the amniotic fluid, filter it through his kidneys and pass it out again as urine. Recycling starts much sooner than people think! Your baby also excretes some fluid from his lungs. Any excess fluid will be absorbed through the amniotic sac or via the umbilical cord, maintaining an ideal balance of fluid for your growing baby.
How much fluid should I have?
Amniotic fluid increases throughout the first two trimesters, peaking at about 34 weeks. After that it declines slowly until birth. If you’re found to have too little fluid at any point in your pregnancy, it’s called oligohydramnios (see below). When there’s too much, it’s called polyhydramnios (see below).
Not enough amniotic fluid – Oligohydramnios
Oligohydramnios is the medical term meaning insufficient amniotic fluid. About 8 percent of all pregnant women are found to have low amniotic fluid at some point, usually in their third trimester. And of the women who go past their due date, 12 per cent will have low amniotic fluid. As it is the baby who determines how much amniotic fluid is produced, the cause of oligohydramnios is usually because of a condition in the foetus. It is not hereditary. It is not always known why low amniotic levels occur but some of the more common reasons include:
- Leaking membranesThis can happen at any time in your pregnancy but more likely as you near your due date. The biggest risk here is the possibility of infection to both you and your baby. You will be monitored closely for signs of infection.
- Placenta problemsSometimes the placenta cannot provide enough nutrients to your baby which in turn stops him from producing much fluid. Amniotic fluid is a product (in part) of maternal circulation, and if the circulation of blood through the placenta is poor, then it is logical that the amount of liquor may start to decrease.
- Twin to twin transfusion syndrome (TTTS)This occurs in some identical twin pregnancies. There is a problem with the placenta which means one twin (the recipient) receives all the nutrients, resulting in too much amniotic fluid whilst the second twin (the donor) receives no nutrients, resulting in too little fluid. There are many treatments available now including using a laser or needle to divide the membrane between the twins to allow a more even flow of fluid.
- Foetal abnormalitiesIf you have low fluid in your first or second trimester it can often mean that the baby has some form of birth defect such as kidney problems or congenital heart problems and often these kind of problems mean that the baby will not survive.
Some people believe that maternal fluid intake can influence the amniotic fluid and you may be asked to drink plenty of water if you have low amniotic fluid. Bed rest is also suggested, especially in the third trimester.
Too much amniotic fluid – Polyhydramnios
This is when you have too much amniotic fluid. Most of the time experts do not know the cause and in two thirds of cases there is nothing wrong and the problem goes away on its own. You may suspect polyhydramnios if you are bigger than your dates suggest. There is a slight risk of premature rupture due to the pressure of the extra fluid. You will be monitored closely. However, sometimes there is a reason for polyhydramnios the most common of which are:
- DiabetesIf you are diabetic and not tightly controlled, you are at risk of having too much fluid, especially in the third trimester. Sometimes women can develop gestational diabetes and because of this, if you are diagnosed with polyhydramnios your midwife will probably check your urine for sugar.
- Twin to twin transfusion syndrome (TTTS)Just as the donor twin in this syndrome will have too little fluid, the recipient twin will have too much which may put a strain on his heart.
- Twins, triplets or more.Multiple pregnancies often result in an excess of amniotic fluid.
- Foetal abnormalitiesConditions that make it difficult for your baby to swallow the amniotic fluid could lead to excess fluid as his kidneys will continue to make urine. These sort of conditions include pyloric stenosis and cleft lip and palate.
The biggest risk with too much fluid is early labour. Also, your waters could break with a large gush which increases the risk of cord prolapse or placental abruption, both of which could cut off your baby’s oxygen supply. Sometimes emergency caesareans are necessary.
Any other risks I should know about?
Fortunately, for most pregnant women the amniotic fluid does exactly what it is supposed to do. It protects your growing baby and keeps your uterus free from infection. We have mentioned the more common complications to do with amniotic fluid above. Below are two other very rare conditions that can cause serious complications. They are:
Amniotic Band Syndrome
This is a set of congenital birth defects believed to be caused by parts of the developing baby getting caught in string-like bands in the womb.
Also known as ABS, this condition occurs in one in 12000 births and tends to affect primarily fingers and toes, which can be shorter or completely missing. It is believed that the inside membranes rupture while the outside ones remain intact, which causes stringy pieces of placenta to float in the amniotic fluid and entangle around the baby, usually fingers, cutting off the blood supply. The condition is not hereditary or genetic but babies with ABS often have other conditions such as clubfoot (in a third of babies) and cleft lip or palate. Treatment options include surgery in utero, when the bands are severed whilst the baby is still in the womb to prevent the restriction of blood. Sometimes the baby may be born with a necrosed (dead) digit, in which case it would need to be amputated.
Amniotic Fluid Embolism (AFE)
This is an extremely rare but fatal condition which can kill as many as half the women it affects. In the UK there are about 3 cases a year and very little is known about the condition. AFE is an obstetric emergency which occurs when amniotic fluid, foetal cells, hair or other debris enters the mother’s blood stream via the placenta and triggers an allergic reaction, causing cardiac and respiratory failure. It will only happen if three other events occur. These are; Ā· Rupture of membranes Ā· Rupture of the veins in the uterus or cervix Ā· Increased pressure from uterus to vein Small traces of foetal tissue are common in pregnancy but in some women it can trigger AFE. It can occur before, during or after delivery and 50 per cent of women will die from it within the first hour. Survivors may have neurological problems. It is not thought that it is hereditary or genetic. Characteristics include larger than normal babies, late deliveries (beyond 42 weeks), hard labour, sudden onset of shock, nausea, vomiting, shortness of breath and chills. The cause is unknown and the condition is unpredictable and unpreventable, but thankfully extremely rare.