Oligohydramnios, or low amniotic fluid, is the opposite of polyhydramnios. Low fluid is usually detected close to the third trimester and often occurs near the end of your pregnancy, especially with prolonged gestation.
What causes oligohydramnios?
It’s normal for amniotic fluid levels to fluctuate within certain parameters. Baby’s urine can temporarily increase fluid levels, while their lung function — which requires fluid — temporarily decreases it. Babies can also swallow amniotic fluid, or it can be absorbed into your bloodstream. The amniotic fluid is replaced every three hours, and a deficiency can indicate that either too little is produced or too much of it is absorbed.
Between weeks 20 and 40, the baby produces ten times more urine, so amniotic fluid should be more abundant. But if the baby’s kidneys are not working properly, fluid levels will not rise. Kidney pathologies in the baby are the most common causes of oligohydramnios.
The second most common cause is the excessive absorption of amniotic fluid. That often happens as a result of placental insufficiency [1], which results from hypertension during pregnancy [2].
If oligohydramnios isn’t caught on my second trimester screening, can it be detected later?
Additional ultrasounds may be ordered if the expectant mother notices the baby is moving less, or if she has abdominal pain. The doctor might also order an ultrasound because uterine or abdominal measurements don’t correspond to normal numbers for that stage of pregnancy. These are the scenarios in which oligohydramnios are caught early.
Unfortunately, oligohydramnios is often detected until delivery. Vaginal birth may be difficult or impossible at that point [3].
Why is amniotic fluid deficiency dangerous?
Firstly, it’s dangerous because it may be a result of a dysfunction in the baby’s kidneys.
Secondly, the lack of fluid means the baby will have reduced mobility. There’s a higher risk that they will be stuck in a position that makes vaginal birth difficult. Reduced mobility can also cause a compression of the chest, which prevents the baby’s lungs from developing normally and can lead to oxygen deprivation [2]. Both issues will prompt a cesarean (C-section).
Lastly, oligohydramnios is often associated with developmental delay and even babies born at full term will look premature [1].
One thing to note: a slight deficiency in amniotic fluid that appears after week 30 of pregnancy is usually not a cause for concern. While your doctor will want to monitor it, it should not prevent a vaginal birth or affect the health of the baby [2].
Can we prevent or cure oligohydramnios?
There is nothing that can be done to prevent oligohydramnios, but attending your prenatal appointments will help your doctor monitor how your pregnancy is progressing while considering any risk factors you may have for this condition. So don’t miss any consultations and follow your doctor’s advice.
