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What is the Evidence for Induction for Low Amniotic Fluid in a Healthy Pregnancy?

By Rebecca L. Dekker, PhD, RN, APRN

Today’s post on the Evidence for Induction for Low Amniotic Fluid in a Healthy Pregnancy is a guest post by blogger Rebecca Dekker, owner of  the fairly new blog in the birth world, Evidence Based Birth that has been  very well received and enjoyed by many.  Look for an interview with Rebecca in an upcoming post where we will learn how this Assistant Professor of Nursing who teaches pathopharmacology and studies depression in patients with heart failure ended up writing the Evidence Based Birth blog appreciated by birth professionals.  I look forward to future posts and collaboration with Rebecca and thank her for her contribution today.- SM

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This question came from one of my readers:

“Low fluid seems to be the new “big baby” for pushing for induction. What does the research say about low fluid at or near term? From what I’ve been able to see in research summaries at least, there appears to be no improved outcome for babies, but I’d love to see the research really hashed out. I’m also curious about causes of low fluid (theorized or known), risks of low fluid, and perhaps as important if not more so, measurements of low fluid.”

This is a great question and I felt like it was a perfect topic for my first article for Science and Sensibility. Standard of practice in the U.S. is to induce labor at term if a mother has low amniotic fluid in an otherwise healthy pregnancy. In fact, 95% of physicians who practice maternal-fetal medicine feel that isolated oligohydramnios—low amniotic fluid in an otherwise healthy pregnancy—is an indication for labor induction at 40 weeks (Schwartz, Sweeting et al. 2009).

But what is the evidence for this standard birth practice? Let’s take a look at the evidence together.

First of all, what is oligohydramnios?

Oligohydramnios means low fluid inside the amniotic sac.

(oligo = little, hydr = water, amnios = membrane around the fetus, or amniotic sac).

Not sure how to pronounce oligohydramnios? Click here.

It is standard of care in the U.S. to induce women with isolated oligohydramnios at term.
Image Source drewesque 

What is amniotic fluid, and what does it do?

During pregnancy, the baby is surrounded by a liquid called amniotic fluid. Amniotic fluid helps protect the baby from trauma to the mother’s abdomen. Amniotic fluid cushions the umbilical cord, protects the baby from infection, and provides fluid, space, nutrients, and hormones to help the baby grow (Brace 1997).

During the second half of pregnancy, amniotic fluid is made up of the baby’s urine and lung secretions. This liquid originally came from the mother, and then flowed through the placenta, to the baby, and out through the baby’s bladder and lungs (Brace 1997).

This same amniotic fluid is then swallowed by the baby and re-absorbed by the lining of the placenta. Because the mother’s fluid levels are the original source of amniotic fluid, changes in the mother’s fluid status can result in changes in the amount of amniotic fluid. Amniotic fluid levels increase until the mother reaches about 34-36 weeks, and then levels gradually decline until birth (Brace 1997).

What can cause low amniotic fluid at term?

Both mother and baby factors can contribute to low amniotic fluid at term.

Mother factors:

  • If the mother is dehydrated, this may lower the amniotic fluid levels. (Patrelli, Gizzo et al. 2012)
  • Women are more likely to be diagnosed with low amniotic fluid levels during the summer, possibly because of dehydration. (Feldman, Friger et al. 2009)
  • If a woman with low amniotic fluid levels at term drinks at least 2.5 Liters of fluid per day, she increases the likelihood that her amniotic fluid levels will be back up to normal by the time of delivery. (Patrelli, Gizzo et al. 2012)
  • If the mother rests on her left side before or during the fluid measurement, this can increase amniotic fluid levels. (Ulker, Temur et al. 2012)
  • If the mother’s water has broken (membranes ruptured), this will lead to a decrease in amniotic fluid. (Brace 1997)
  • If the mother’s placenta is not acting sufficiently anymore, this may lead to a decrease in amniotic fluid. When this happens, it may be because the mother has a serious condition such as pre-eclampsia or intrauterine growth restriction. (Beloosesky and Ross 2012)

Baby factors:

  • If the baby has a problem with the urinary tract or kidneys, this may decrease the flow of urine. (Brace 1997)
  • In the 14 days before the start of spontaneous labor, the baby’s urine output starts to decrease. (Stigter, Mulder et al. 2011)
  • As the baby gets closer to term, the baby swallows more amniotic fluid, thus leading to a decline in fluid levels. (Brace 1997)
  • If the baby is post-term (after 42 weeks), he or she begins to swallow significantly more fluid, contributing to a decline in amniotic fluid. (Brace 1997)
  • If the baby has a birth defect, he or she may swallow significantly more fluid, leading to low amniotic fluid levels. (Beloosesky and Ross 2012)

What is the best way to measure amniotic fluid levels?

The gold-standard method is to inject the amniotic sac with dye and then take samples of the amniotic fluid to check the dilution. However, this method is very invasive. So the most commonly used methods instead are 2 ultrasound techniques:  the amniotic fluid index (AFI) and the single deepest pocket (Gilbert 2012).

To calculate the AFI, the technician divides the uterus into 4 areas. The largest fluid pocket in each area is measured, and then these 4 numbers are added make up the AFI. An AFI value of 5 cm or less is considered oligohydramnios. With the single deepest pocket method, the technician looks for the largest pocket of amniotic fluid in the uterus. If the largest pocket is less than 2 cm by 1 cm, then that is considered a diagnosis of oligohydramnios (Nabhan and Abdelmoula 2009).

It is important to understand that amniotic fluid levels exist on a continuum and that there is no agreement among researchers about the cut-off value that predicts poor outcomes—the AFI level of 5 was arbitrarily chosen to define oligohydramnios (Nabhan and Abdelmoula 2009). Furthermore, a large body of research has shown that both AFI and single deepest pocket are poor predictors of true amniotic fluid volume. For example, the AFI catches only 10% of all cases of true oligohydramnios (10% sensitivity)(Gilbert 2012).

There are several factors that make it difficult to get an accurate ultrasound measurement. As fluid levels decrease, ultrasound results become less accurate. Inexperience on the part of the technician can reduce the accuracy of the test results, as well as the amount of pressure that the technician puts on the ultrasound probe. The position of the baby can also affect the accuracy of the results. (Nabhan and Abdelmoula 2009; Gilbert 2012).

So which is the best way to measure amniotic fluid?

In a Cochrane review, researchers combined the results from 5 randomized controlled trials with more than 3,200 women. In these studies, women were randomized to either the AFI method or the single deepest pocket method. Researchers found that when the AFI is used to measure amniotic fluid, women were 2.4 times more likely to be diagnosed with oligohydramnios, 1.9 times more likely to be induced, and 1.5 times more likely to have a Cesarean for fetal distress without any corresponding improvement in infant outcomes. The researchers concluded that the single deepest pocket measurement has fewer risks and should be the preferred way to measure amniotic fluid (Nabhan and Abdelmoula 2009).

What is the clinical significance of low amniotic fluid when a mother reaches 37 or more weeks?

In 2009, 91% of physicians believed that isolated oligohydramnios, or low amniotic fluid in an otherwise healthy pregnancy at term, was a risk factor for poor outcomes (Schwartz, Sweeting et al. 2009).

In the U.S., 91% of maternal-fetal physicians believe that isolated oligohydramnios at term is a risk factor for poor outcomes, and 95% will recommend labor induction.
Image Source robenjoyce

However, this belief is not accurate. In early studies on amniotic fluid and outcomes, researchers included babies with congenital defects , women with pre-eclampsia or intrauterine growth restriction (IUGR), and women who were post-term (past 42 weeks) in their samples. These women and babies are more likely to have low amniotic fluid, and they are also much more likely to have poor outcomes. So although early researchers found that babies born to women with low amniotic fluid had higher perinatal mortality rates (Chamberlain, Manning et al. 1984), higher Cesarean rates for fetal distress, and lower Apgar scores (Chauhan, Sanderson et al. 1999), the poor outcomes were due to the complications—not the low amniotic fluid (Gilbert 2012).

So, if a woman has TRUE ISOLATED oligohydramnios at term, meaning low amniotic fluid in a healthy pregnancy with a healthy baby at term (between 37 and 42 weeks), what are the risks?

There is no evidence that isolated oligohydramnios at term is a risk factor for poor outcomes. However, induction for isolated oligohydramnios leads to higher Cesarean rates. In a systematic literature review, I found 5 studies from the last 10 years. I will discuss the 3 highest quality studies here. For results from all 5, you can see my findings summarized in this Google document table here.

  1. Locatelli et al. (2003) studied 3,049 healthy pregnant women who were between 40 and 41.6 weeks pregnant. The purpose of this study was to find out if low amniotic fluid (defined as AFI ≤ 5) led to poor outcomes. Eleven percent of women had low amniotic fluid, and these women had higher induction rates (83% vs. 25%), higher Cesarean rates (15% vs. 11%), and higher Cesarean rates for non-reassuring fetal heart rates (8% vs. 4%). Babies born to women with low amniotic fluid were more likely to have birth weights beneath the 10th percentile (13% vs. 6%). There were no differences between groups with meconium staining, meconium aspiration, umbilical artery pH <7, or Apgar scores. There was only one stillbirth (in the normal fluid group) for a true knot in the umbilical cord.

After controlling for the fact that some women were induced and some women were having their first baby, the researchers found no association between Cesarean for non-reassuring heart rate and amniotic fluid. This means that the inductions were probably responsible for the higher Cesarean rates in the low amniotic fluid group. However, when the researchers controlled for gestational age, they found that the association between low birth weight and low amniotic fluid remained significant. This means that women with low amniotic fluid were 2 times more likely to have a baby that is born beneath the 10th percentile. These babies may have had undiagnosed fetal growth restriction (IUGR), which is a separate risk factor for poor outcomes.

  1. Manzaneres et al. (2006) compared outcomes from 206 healthy pregnant women who were induced for isolated oligohydramnios at term and 206 healthy pregnant women with normal amniotic fluid levels who went into spontaneous labor.  The women in both groups delivered between 37 and 42 weeks. The researchers found that the low amniotic fluid group was more likely to require forceps or vacuum delivery (26% vs. 17%), Cesarean delivery (16% vs. 6%), and have non-reassuring fetal status during labor (8% vs. 2%). The non-reassuring fetal status may have been due to the induction medications, but this explanation was not proposed by the authors. There were no differences between groups with birth weight, Apgar scores, meconium staining, neonatal admissions, or umbilical cord pH. In summary, the authors found that inducing labor for isolated oligohydramnios at term increased Cesarean and operative vaginal delivery rates without any improvement in newborn outcomes.
  1. There was one small pilot study done in which researchers randomized women with isolated oligohydramnios at term to induction or watchful waiting. The researchers randomly assigned 54 women who were 41 weeks pregnant to either induction or watchful waiting. There were no differences between groups in any outcomes, including birth weight, Cesarean delivery, Apgar scores, or neonatal admission. This study was limited by its small sample size and the fact that it only included women who were 41 weeks pregnant (Ek, Andersson et al. 2005).

So what is the evidence for induction because of low amniotic fluid (without any other complications) at term?

There is no evidence that inducing labor for isolated oligohydramnios at term has any beneficial impact on mother or infant outcomes. Based on the lack of evidence, any recommendation for induction for isolated oligohydramnios at term would be a weak recommendation based on clinical opinion alone.

In summary, this is what I found about low amniotic fluid in an uncomplicated pregnancy at term (37-42 weeks):

  • Ultrasound measurement is a poor predictor of actual amniotic fluid volume
  • The single deepest pocket method of measurement has fewer risks than the AFI
  • Poor outcomes seen with low amniotic fluid are usually due to underlying complications such as pre-eclampsia, birth defects, or fetal growth restriction
  • The main risk of low amniotic fluid at term in a healthy pregnancy is induction (and Cesarean delivery as a result of the induction) and potentially the risk of lower birth weight
  • Current evidence does not support induction for isolated oligohydramnios at term

Are women in your local areas being induced for isolated oligohydramnios at term? Are consumers and clinicians aware of this evidence? What is the standard of practice for evaluating amniotic fluid in your local facilities, AFI or Single Deepest Pocket? How do you discuss this in your classes and with your patients, clients and students?

References

  1. Beloosesky, R. and M. G. Ross. (2012). “Oligohydramnios.”   Retrieved 8/20/12, 2012, from www.UpToDate.com
  2. Brace, R. A. (1997). “Physiology of amniotic fluid volume regulation.” Clin Obstet Gynecol 40(2): 280-289.
  3. Chamberlain, P. F., F. A. Manning, et al. (1984). “Ultrasound evaluation of amniotic fluid volume. I. The relationship of marginal and decreased amniotic fluid volumes to perinatal outcome.” Am J Obstet Gynecol 150(3): 245-249.
  4. Chauhan, S. P., M. Sanderson, et al. (1999). “Perinatal outcome and amniotic fluid index in the antepartum and intrapartum periods: A meta-analysis.” Am J Obstet Gynecol 181(6): 1473-1478.
  5. Ek, S., A. Andersson, et al. (2005). “Oligohydramnios in uncomplicated pregnancies beyond 40 completed weeks. A prospective, randomised, pilot study on maternal and neonatal outcomes.” Fetal Diagn Ther 20(3): 182-185.
  6. Feldman, I., M. Friger, et al. (2009). “Is oligohydramnios more common during the summer season?” Arch Gynecol Obstet 280(1): 3-6.
  7. Gilbert, W. M. (2012). Amniotic Fluid Disorders. Obstetrics: Normal and Problem Pregnancies. S. G. Gabbe. Philadelphia, PA, Elsevier. 6.
  8. Locatelli, A., P. Vergani, et al. (2004). “Perinatal outcome associated with oligohydramnios in uncomplicated term pregnancies.” Arch Gynecol Obstet 269(2): 130-133.
  9. Nabhan, A. F. and Y. A. Abdelmoula (2009). “Amniotic fluid index versus single deepest vertical pocket: a meta-analysis of randomized controlled trials.” International journal of gynaecology and obstetrics: the official organ of the International Federation of Gynaecology and Obstetrics 104(3): 184-188.
  10. 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.
  11. Schwartz, N., R. Sweeting, et al. (2009). “Practice patterns in the management of isolated oligohydramnios: a survey of perinatologists.” J Matern Fetal Neonatal Med 22(4): 357-361.
  12. Stigter, R. H., E. J. Mulder, et al. (2011). “Fetal urine production in late pregnancy.” ISRN Obstet Gynecol 2011: 345431.
  13. Ulker, K., I. Temur, et al. (2012). “Effects of maternal left lateral position and rest on amniotic fluid index: a prospective clinical study.” J Reprod Med 57(5-6): 270-276.
About Rebecca Dekker
Rebecca Dekker, PhD, RN, APRN, is an Assistant Professor of Nursing at a research-intensive university and author of www.evidencebasedbirth.com. Rebecca’s vision is to promote evidence-based birth practices among consumers and clinicians worldwide. She publishes summaries of birth evidence using a Question and Answer style.

 

 

 

Evidence Based Medicine, Fetal Monitoring, Guest Posts, Healthy Birth Practices, Healthy Care Practices, informed Consent, Maternity Care, Medical Interventions, Systematic Review, Uncategorized , , , , , , , , ,

  1. avatar
    Tara
    May 6th, 2014 at 18:45 | #1

    And my midwife used the deepest pocket method for measuring fluid which she showed me and my baby did have distress with heart rate issues, but we still made it thanks to my midwife! :D

  2. avatar
    Noelle
    May 11th, 2014 at 19:06 | #2

    This article is upsetting to me. If low amniotic fluid wasn’t a problem, then why are we even discussing it? If low amniotic fluid is currently a sign of labor induction them I believe your article missed the mark. I am concerned with Doctors like yourself creating this false sense for women that there’s no alarm needed when your baby is not being properly “cushioned” or supported. I lost my daughter at full term due to HIE. I had low amniotic fluid and underwent an induction. I believe my daughter was in distress for many hours if not days due to low amniotic fluid. I’m tired of nurses, doctors and others in the medical profession encouraging mothers to just “go home, relax… Things that your body is doing is natural. I believe almost no amniotic fluid is not natural is does contribute to stress on a baby. Please please please take writing these articles seriously, as these were the things I was reading that did not put me on the alert I needed to be on.

  3. avatar
    Melody Samuelson
    May 31st, 2014 at 22:29 | #3

    This article is also upsetting me. I lost my full term beautiful perfectly formed granddaughter (per autopsy) because a midwife at a hospital did not catch this complication (along with not calling her supervising physician) when my daughter was greater than 4cm and overdue when the baby was displaying signs of distress. Although it is a rare complication, it does happen and to minimize the “poor outcomes” is a disservice to pregnant mothers. We would give anything to have a C section that night when she was “just dehydrated.”

  4. avatar
    Melody Samuelson
    May 31st, 2014 at 22:33 | #4

    Again, we would give anything to have a C section for my perfect granddaughter who was a “poor outcome” when low amniotic fluid was missed by a midwife.

  5. avatar
    moi
    June 23rd, 2014 at 13:35 | #5

    You both very clearly (and sadly) highlight the extreme seriousness of low amniotic fluid. It is a problem for the little ones, and induction I imagine would be hard on the baby (and mum), given they have no fluid-cushion to support them ?? I still believe, c-section is the best/safest option, in this scenario.

    I am so very sorry to you both on the loss of your beautiful little ones.
    How very sad.

  6. avatar
    Jenny
    July 1st, 2014 at 07:54 | #6

    Hello Rebecca. This is interesting information. I appreciate the time you have spent digging into the literature. As a NP, it can be time consuming at least! I was wondering yoru thoughts on isolated oligohydramnios repeating itself in subsequent pregnancies? I had oligo with my first pregnancy, which was diagnosed at my 40 wk appointment after a failing fetal non-stress test. My son’s HR’s had been in the 90′s for extended periods of time, so he was likely compressing his cord. The ultrasound showed a measurement of no fluid (the doctor saw some in his bladder, but there was none he could measure that was surreounding him). So we had to be induced. Since it was a first birth, and my cervix was not ready at all, the induction took 33 hours start to finish. Thank God for our awesome midwife who helped us have a vaginal birth!

    My second pregnancy was a little girl. The doctor did several extra ultrasounds, which I did not think were necessary, and cost a lot of $$ for us, but I said ok anyway. Our fluid measurements were ok (I think around 8 near the end), and she was born by spontaneous vaginal birth at 40 weeks 5 days.

    We are expecting again, and are considering a home birth attended by CPMs who have loads of birth experience. However, my only reservation is if oligohydramnios will repeat itself. I would plan to stay with my OB through at least the 20 week ultrasound to assure everything is progressing normally. I have had very normal, healthy pregnancies, and babies, in the past. But it would stink to plan a home birth and then need to be induced anyway, or go to the hospital because of the baby’s heartrates showing distress. We are still very early in the pregnancy, and have yet to meet with the midwives, and my OB. But I did not know if you have seen in the literature any info about oligo repeating itself in subsequent pregnancies. (Also, as a side note, I know a lot of medical professionals look down on home births, but in all the reading I have done, there is no evidence that says delivery in a hospital is safer if the pregnancy is healthy and normal. At least we are 8 minutes from the hospital if a problem should arise! But it would stink to pay for both the midwives, and the hospital birth!).

    Thank you for all the information you have provided!

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