What is Amniotic Fluid and why is it so important?
Amniotic Fluid is the fluid that surrounds and protects a baby in the womb. It acts as a protective cushion from any trauma that occurs to the maternal abdomen. It also provides a cushion for the umbilical cord from compression. The amniotic fluid also has antibacterial properties to protect the baby from infection. It provides enough space and growth factor to allow for normal development of the baby in the womb, to include the musculoskeletal system, gastrointestinal system, and pulmonary system. Healthcare providers then use the amniotic fluid volume to predict fetal outcomes and the progression of the pregnancy.
It is made up of proteins, electrolytes, vitamins, and immunoglobulins from the birthing person. The actual content of amniotic fluid depends on where the baby is at in gestation. From conception to around 8-12 weeks gestation, it is made up of nutrient rich fluid called the coelomic fluid that acts almost like a second placenta by providing nutrients for the baby as the amniotic cavity grows, and it also contains maternal serum. After that the amniotic fluid is mostly made up of baby’s urine and lung secretions. It also contains other nutrients like carbohydrates, peptides, lipids, etc. It’s clear in color due to the low amount of protein in the fluid.
Amniotic fluid levels that are too high or too low have been correlated with poor outcomes for babies. So clinicians monitor the levels in most pregnancies, especially when any signs of fetal distress is noted. Normal level of Amniotic fluid is Amniotic Fluid Index (AFI) between 5-24, or a Single Deepest Pocket (SDP) between 2-7cm.The regulation of the Amniotic fluid level is mostly done by baby swallowing the amniotic fluid and then baby will urinate the amniotic fluid out. Babies also use the amniotic fluid when they’re doing their practice breathing in utero.
Polyhydramnios: Too Much Fluid
Polyhydramnios is when there is too much amniotic fluid, which is usually an AFI of more than 24cm or a SDP of 8cm or more. Polyhydramnios can be a sign of gastrointestinal tract obstruction such as esophageal atresia, genetic disorders, musculoskeletal disorder, or congenital diaphragmatic hernias in baby. Especially when Polyhydramnios is considered a moderate or severe case.
Signs that poly may be present is when the abdomen is measuring 3+ weeks ahead during their routine prenatal appointment. The birthing person might report feels short of breath as the pregnancy progresses because the uterus is larger than normal at that time. The uterus may also be irritated because it is being overstretched which could cause cramping prior to labor.
During labor this can be an issue because baby may not engage in the pelvis because of all the fluid, and if the water breaks spontaneously prior to head engagement this can increase the risk of a prolapsed umbilical cord. I have seen providers do a “controlled Artifical Rupture of Membranes” when poly is present to allow fluid to come out slowly to lessen the chance of the prolapsed cord. Then this allows the baby to engage into the pelvis and put pressure on the cervix for labor to occur.
Oligohydrammnios: Not Enough Fluid
Oligohydrammnios is when there is not enough amniotic fluid, which is usually an AFI of less than 5cm or SDP less than 2cm. Oligohydramnios can be a sign of renal agenesis, GI tract obstruction, and IUGR. It can also be a sign of dehydration in the birthing person so there’s some research that supports if Oligo is noted in the birthing person, for IV rehydration or for the birthing person to increase their fluid intake and re-evaluating this level.
I have seen that before diagnosis a lot of the time the birthing person reports a decrease in the fetal movement to their provider.
When Oligo/Poly is noted it usually leads to some interventions, such as ultrasounds, closer monitoring, or induction.
Oligohydramnios is noted to be more serious and induction is usually offered when it is diagnosed. Compared to Polyhydramnios they sometimes wait till 38/39 weeks to induce. Every situation can be different depending on multiple factors though.