Most pregnant women don’t even think about their baby’s amniotic fluid levels, until their healthcare provider tells them it could be a problem.
Some women are told they have too little or too much amniotic fluid.
But what does this mean for a mother and her unborn baby?
This article will explain everything you need to know in simple terms, in case the topic of amniotic fluid levels comes up in the future.
What is amniotic fluid?
Within days of an egg being fertilized, the amniotic sac begins to form and fill with fluid.
The amniotic sac is sometimes known as the membranes; it is a thin-walled sac that contains your baby and the amniotic fluid.
The amniotic fluid acts as a buffer to protect the developing baby, cushioning against any bumps or injury.
It also allows your baby to move around easily, which promotes muscular and skeletal development.
Amniotic fluid swallowed by the baby helps to form the gastrointestinal tract. The fluid fills the baby’s lungs – another important part of fetal development.
Swallowing is an important developmental skill babies practice in the uterus for many months, in preparation for breastfeeding after birth.
The fluid forms urine and maintains a constant temperature for the baby.
Although it might not seem very important, amniotic fluid is actually vital for your baby’s development.
What does amniotic fluid consist of?
At the beginning of pregnancy, the amniotic fluid is initially created from the mother’s plasma, the pale yellow liquid component of blood.
Gradually, the maternal contribution will decrease and the baby’s urine will make up most of the fluid.
Apart from water (fetal urine), the amniotic fluid is also composed of:
- Nutrients, such as zinc, copper, folate, and iron.
- Hormones, such as prolactin, progesterone, prostaglandins, androgens
- Baby’s skin protectors like vernix and lanugo, which are shed into the amniotic fluid.
Until the 12th week of pregnancy, amniotic fluid is mostly water, with electrolytes.
In the second trimester, proteins, carbohydrates, lipids, and urea are present; these aid in the baby’s growth.
From around 16 weeks of pregnancy, the baby’s kidneys begin to function, and fetal urine becomes the main source of amniotic fluid.
The other source of amniotic fluid is fluid excreted from the baby’s lungs.
Initially, the amniotic fluid is absorbed by the baby’s skin and tissue.
At around 20 weeks of pregnancy, the skin begins to change, and the fluid is ingested rather than absorbed.
Amniotic fluid levels
During pregnancy, as your baby grows and develops inside the uterus, he is protected by the amniotic sac (membranes), and surrounded by amniotic fluid.
You take this fact for granted, and probably don’t really think much about it until you get close to giving birth. Then you start to worry about your waters breaking in the middle of aisle three at the supermarket!
How much fluid should be present can become a concern for some women during pregnancy.
As the baby grows, it produces more amniotic fluid. The amount increases until the baby is about 32 weeks gestation.
The amniotic fluid volume then remains constant until the baby is full-term (37 to 42 weeks), when the levels start to decline.
Small changes in the amniotic fluid levels occur over time as the baby swallows the fluid.
In some pregnancies, there might be too much (polyhydramnios) or too little (oligohydramnios) amniotic fluid.
In order for your baby to develop properly, it’s important there’s neither too much nor too little amniotic fluid.
Normal amniotic fluid index chart
If your healthcare providers are concerned about the levels of amniotic fluid, they will refer you to have an ultrasound scan. This is done to check for normal amniotic fluid volume and to see whether there are any causes for concern.
There are two ultrasound measurements used to measure the amniotic fluid levels surrounding the baby:
- Amniotic Fluid Index (AFI). This method uses the sum of four of the deepest vertical pockets of fluid. The normal range for the AFI is 5-25 cms (depending on gestational age).
- Single Deepest Pocket (SDP). This method measures the depth of the largest visible pocket of fluid surrounding the fetus. The normal range for maximum pool is 2-8 cms.
A review comparing AFI and SDP found the use of AFI results in over-diagnosis of too little fluid (oligohydramnios).
This leads to unnecessary interventions, such as induction, which contributes to an increased risk of injury or death, without any improvement in perinatal outcomes.
Both AFI and SPD are qualitative measures of the amniotic fluid volume. This means the measurements are estimates rather than a true measurement of the fluid present.
There is also no clear definition of normal/abnormal measurements of amniotic fluid volume across gestation for care providers to base their diagnosis of high or low levels on.
Measuring amniotic fluid is sometimes not very reliable as the fluid pockets around the baby aren’t precisely measured via ultrasound scan.
Low amniotic fluid
Oligohydramnios is diagnosed when there is not enough amniotic fluid volume surrounding the baby.
It’s diagnosed when the amniotic fluid index (AFI) measurement is below 5 or 6 cm (depending on baby’s gestational age), and the single deepest pocket (SDP) is less than 2 cm.
Approximately 4% of pregnant women are diagnosed with oligohydramnios.
In most cases, the cause of oligohydramnios is unknown.
As pregnancy progresses past 37 weeks, the fluid levels naturally decline.
You can read more in Low Amniotic Fluid Levels – Oligohydramnios.
Does low amniotic fluid mean c-section?
Each mother-baby unit is unique, and some might simply have lower levels than those considered to be average.
Maternal hydration levels appear to have an impact as well; a scan might show lower than usual levels one day, but be normal a few days later, depending on how much fluid the mother has taken.
If the amniotic sac has ruptured and developed a slow leak, this can also contribute to lower levels of fluid.
A review of research literature shows, in a healthy full-term pregnancy, oligohydramnios isn’t linked to complications but does increase the risk of interventions.
This means the risk of having a c-section due to low amniotic fluid volume depends more on the healthcare provider’s willingness to intervene than the low amniotic fluid index itself.
In certain situations, there are problems with the baby’s kidneys or placental function.
These are more likely to occur with medical conditions such as pre-eclampsia.
Babies in these situations are usually small for dates and can be easily felt through the mother’s abdomen.
Too much amniotic fluid
Polyhydramnios is a high amniotic fluid volume, or too much fluid surrounding the baby.
It’s diagnosed when the SDP measurement is greater than 8 cm or the AFI measurement is greater than 25 cm.
About 2% of women experience polyhydramnios and it’s usually not known what causes the increase in fluid.
Certain factors that are associated with polyhydramnios are:
- Maternal diabetes, including gestational diabetes.
- Twin pregnancy
- Build-up of fluid in certain areas of the baby’s body, called hydrops fetalis
- Blockage in the baby’s gut, which prevents him from absorbing amniotic fluid (gut atresia)
- Baby producing too much urine
- Baby not swallowing enough fluid
- Genetic problems with the baby
- Overgrowth of placental blood vessels (chorioandioma).
Be sure to read Too Much Amniotic Fluid | What You Need To Know About Polyhydramnios for more information.
Is it bad to have a lot of amniotic fluid?
Complications of polyhydramnios tend to include an increased risk of preterm labor, due to the pressure being placed on the uterus with the extra fluid.
Babies are also more likely to move into positions that aren’t ideal for birth.
This could mean the umbilical cord might slip in front of the baby’s head, causing cord prolapse, which is a medical emergency.
Placental abruption is another medical emergency, which can occur with a sudden increase in fluid volume.
While most of these complications are rare, it’s likely your care provider will want to do some investigation to see if there is an underlying cause of polyhydramnios.
In about 60% of cases, there is no known cause.
Depending on the cause, and on how many weeks pregnant you are, there are a number of treatment options.
In some situations, excess amniotic fluid can be removed via a needle (amniodrainage); this can reduce the risk of premature labor.
If there is a more urgent need to have the baby born sooner, your care provider might rupture your membranes, while holding the baby in place.
This controlled induction is carefully managed to avoid prolapse of the umbilical cord but does require quick access to a theatre in case a c-section becomes necessary.
The amniotic fluid plays an important role in the health and development of your growing baby.
If your care provider believes there is a problem with amniotic fluid levels, a number of scans might be necessary to determine whether the volume is normal for you or there is an underlying problem.
As with any intervention, it’s important you are provided with all the necessary information to make an informed decision about your care.
Amniotic fluid leak
Sometimes during pregnancy you might feel your underwear is moist, or even damp, and you wonder whether it might be amniotic fluid.
If this happens after 37 weeks it’s very likely labor is not very far away. Most women go into labor in the first 48 hours following the waters rupturing.
If you haven’t reached full term and you suspect an amniotic leak, contact your healthcare provider straight away. This premature rupture of membranes might lead to labor starting shortly after and your baby being born prematurely.
Although it’s difficult to keep labor from happening, the obstetric team can delay it from happening while they prepare your baby in the best possible way for an imminent premature birth.
Having this time to prepare your baby for a likely preterm birth can have a big impact on how your baby copes with living outside your womb prematurely.
Not all breaking of waters is as clear as when it happens in the movies!
If you suspect an amniotic fluid leak, here is some advice:
- Change your underwear. Avoid white or black as those two colors make it more difficult to identify dampness.
- Put on a pad. Try to use a maternity pad, or one made of fabric, without any ‘plastic’ looking part. If these (the most widely sold in shops worldwide) are all you have, place a piece of cloth, again not black or white, as a pad on your underwear.
- Talk to your baby. Explain that everything is ok. Maybe you could ask her if she felt it or if she’s ok. This will help you both relax while you wait.
- If you feel a slow, constant trickle you can’t control, or you feel a leak when your baby moves or when you apply pressure to your uterine wall (sneezing or coughing), it means the amniotic sac has a leak and some of the fluid is trickling out.
What does amniotic fluid smell like?
Amniotic fluid smell is quite mild-smelling and even sweet. It shouldn’t have a nasty or offensive odor.
It’s full of nutrients for your baby, hormones, and pheromones (smell activating hormones), and it usually makes its appearance during labor or just before.
These pheromones have an impact on the mother’s oxytocin release. When the waters break, the smell of the amniotic fluid tells the woman’s brain to produce more oxytocin, as birth is very close.
Sometimes amniotic fluid can have an offensive smell. This happens when there’s an infection in the uterus.
If you suspect your waters may have broken and you notice an unpleasant smell, contact your midwife or doctor to discuss your plan of care.
Amniotic fluid color
The color of amniotic fluid also indicates whether or not everything is happening as it should.
Amniotic fluid is usually quite clear and pale straw-colored.
Sometimes it can be accompanied by a pink tinge as some very small blood vessels might have started to rupture as uterine activity increases.
If the amniotic fluid appears yellow, it’s important not to confuse it with urine. If you’re unsure whether what you’re leaking is amniotic fluid or urine you should try to identify it by smell.
When the amniotic fluid is yellow or greenish, it might have been caused by meconium, your baby’s first ‘poo’. Meconium in amniotic fluid is often treated as an emergency but it’s important to know it can also happen normally.
Reasons why you might see meconium in amniotic fluid:
- The baby is mature enough and, while continuing to explore his body’s capabilities.. ooopps!
- The baby’s oxygen supply has been momentarily reduced and that has made the anal sphicter relax. At times the umbilical cord is compressed (in baby’s hand, in between mother and baby).
Most babies who have passed meconium in the amniotic fluid can go through labor and birth without any added complications. The baby doesn’t know she’s pooed
The bigger risk lies in the meconium getting into the baby’s lungs, but babies don’t breathe while in utero. Some babies might gasp after a maintained lack of oxygen. This would happen with some rare metabolic disorders, or after a long, sustained pathological labor.
Your healthcare provider will be able to assess your baby’s wellbeing. If your amniotic fluid is yellow, get in touch with your midwife or doctor. Rest assured, this color just means someone will keep an eye on it.
When the color of the amniotic fluid is green, that means the baby has opened his bowels several times, which indicates a more sustained lack of oxygen.
It’s extremely rare to find green amniotic fluid if a woman is not in established labor.
When your baby is in a breech position he will be passing meconium but this is completely normal. It’s the physiological reaction to having your bum leading the way.
You can read more about amniotic fluid stained with meconium in Meconium In Amniotic Fluid.