Oligohydramnios - Low Amniotic Fluid Volume

Woman getting an ultrasound
Photo © Blend Images/Getty Images

Amniotic fluid is the watery cushion that surrounds your baby in pregnancy. It provides space for the baby to grow in the uterus and provides protection for the umbilical cord to protect it from being compressed in the uterus. After about the halfway point in pregnancy, the amniotic fluid comes from a combination of the baby’s urine and secretions from the lungs. The baby also drinks the amniotic fluid and urinates it back out.

After about the 36th week of pregnancy, the amniotic fluid slowly starts to decrease until the birth.

While amniotic fluid can vary in amount, there are two extremes of amniotic fluid that can cause problems or be a sign of problems. The first is known as polyhydramnios, or too much fluid; the second is oligohydramnios, or too little fluid.

Sometimes the amount of amniotic fluid is suspected to be one or the other by palpating the abdomen or measuring the fundal height, both routine practices in prenatal care. If the measurements or off, your doctor or midwife may recommend an ultrasound to check the fluid levels in the uterus.

To use ultrasound to diagnose low amniotic fluid, oligohydramnios, the best way is to use the single deepest pocket measurement.  This is where the largest, deepest pocket of fluid should measure greater than 2 cm by 1 cm to be a healthy level of amniotic fluid. Lower than this and the mother is diagnosed with having oligohydramnios.

Using ultrasound has the advantage of being relatively easy to do and widely available with few risks to the mother, baby, or pregnancy. 

So what causes a mother to have lower amniotic fluid volume? There are a couple of things that are based on the mother’s medical history to include:

  • Dehydration
  • Placental insufficiency
  • Ruptured membranes

There are also baby factors, which may include:

  • Birth defects, including a problem with the baby’s kidneys
  • Growth Restriction (placental insufficiency)
  • Post-term (past 42 weeks)
  • Some medications

In general, there is a slow down in the production of amniotic fluid the closer a mother gets to spontaneous labor. This can be difficult to distinguish from other characteristics. So an induction of labor, simply because the amniotic fluid is low, may not be the safest choice.  You may want to look at all the factors before deciding that this is the route to take.

What can you do about low amniotic fluid? If the suspected cause is dehydration, a mother can drink fluid and rest. This can decrease the risk of dehydration and cause the fluid levels to normalize. Since dehydration is particularly a concern in the summer, this is a general recommendation of many practitioners to stay hydrated. Other factors may not be so obvious and an induction of labor may be the best course of action.

The biggest risk for the vast majority of mothers is the induction that may come from a diagnosis of oligohydramnios. Mothers who have an induction of labor are more likely to have certain interventions including a cesarean birth from the induction. While researchers argue over the cut off for a healthy level of fluid, there are also cases of oligohydramnios that occur with other problems, like known birth defects, or a failed non-stress test. These are more likely to need to treatment than a mother at term with a single instance of low amniotic fluid.

Labor in general may have a higher incidence of fetal distress or cesarean birth, but in most cases this is due more to the cause of the low amniotic fluid volume than the low fluid volume.


  1. Brace, R. A. (1997). “Physiology of amniotic fluid volume regulation.” Clin Obstet Gynecol40(2): 280-289.
  2. Chauhan SP,et al. Ultrasonographic assessment of amniotic fluid does not reflect actual amniotic fluid volume. Am J Obstet Gynecol. 1997 Aug;177(2):291-6; discussion 296-7.
  3. Feldman, I., M. Friger, et al. (2009). “Is oligohydramnios more common during the summer season?” Arch Gynecol Obstet 280(1): 3-6.
  4. Glantz, J. C. (2005). Elective induction vs. spontaneous labor associations and outcomes. Journal of Reproductive Medicine, 50(4), 235-240.
  5. McCurdy CM Jr, Seeds JW. Oligohydramnios: problems and treatment. Semin Perinatol. 1993 Jun;17(3):183-96. PMID:7690990 
  6. Nabhan AF, Abdelmoula YA. Amniotic fluid index versus single deepest vertical pocket as a screening test forpreventing adverse pregnancy outcome. Cochrane Database of Systematic Reviews 2008, Issue 3. Art. No.: CD006593. DOI:10.1002/14651858.CD006593.pub2.
  7. Patrelli, T. S., S. Gizzo, et al. (2012). “Maternal hydration therapy improves the quantity of amniotic fluid and the pregnancy outcome in third-trimester isolated oligohydramnios: a controlled randomized institutional trial.” J Ultrasound Med 31(2): 239-244.


Continue Reading