AFI Research Meta-analysis
Feb 18, 2011 03:34 PM
I am grateful you are still active and providing your scientific analysis. I met you at a DONA conference in San Francisco about 10 years ago. I haven't really looked you up in a while because, like you, I can read. Consequently, I tend to do my own research. However, I have come up against quite a block of information regarding AFI.
I love what you have written regarding shifts in "pockets" as the baby moves and addressing the reason a doctor might be looking at AFI in the first place and the comment regarding risk of induction vs supposed risks of possibly low amniotic fluid.
I have found two studies. One only evaluating 8 women with a variance of .65! The other study had 40 women and not much better accuracy. Are we really using 48 women with such variance to dictate public health? Can you comment on the validity and reliability of the research?
Feb 18, 2011 09:07 PM
The clinically important question with any test is does it accurately discriminate between affected and healthy individuals so that affected individuals can be treated without doing undure harm to healthy ones? The answer with all forms of tests of fetal wellbeing, including amniotic fluid volume measurements, is "no." Here's what I found when doing the research for the induction chapter for the forthcoming new edition of Obstetric Myths Versus Research Realities:
- I could find only one study in 1600 women in which results of amniotic fluid measurements were concealed. (Concealment is important because knowing the results leads to inductions, and inducing labor leads to more fetal distress and cesareans independent of fetal condition.) Low amniotic fluid volume was associated with increased likelihood of low blood pH at birth, but the authors concluded that the sensitivity (test accurately identifies affected individuals) was too low at 29% to make the test useful for identifying at-risk fetuses. We also, of course, don't know if even in compromised fetuses, induction overstressed a fetus who would have been able to tolerate a spontaneous labor.
Morris JM, Thompson K, Smithey J, et al. The usefulness of ultrasound assessment of amniotic fluid in predicting adverse outcome in prolonged pregnancy: a prospective blinded observational study. BJOG 2003;110(11):989-94.
- We have a trial assigning 900 women to routine AFI evaluation at hospital admission in early labor or not. Investigators found that women having AFI doubled their odds of cesarean for fetal distress (6.5% vs. 3.2%) with no difference in neonatal outcomes.
Chauhan SP, Washburne JF, Magann EF, et al. A randomized study to assess the efficacy of the amniotic fluid index as a fetal admission test. Obstet Gynecol 1995;86(1):9-13.
- We have a systematic review of trials comparing two techniques of amniotic fluid volume estimation. More women with AFI were diagnosed with having low amniotic fluid volume than with single deepest pocket (22% vs. 9%), which resulted in more inductions (14% vs. 7.5%) but no differences in neonatal outcomes.
Nabhan AF, Abdelmoula YA. Amniotic fluid index versus single deepest vertical pocket as a screening test for preventing adverse pregnancy outcome. Cochrane Database Syst Rev 2008(3):CD006593.
- Finally, we have a study showing that low amniotic fluid volume in the absence of other symptoms is not concerning. Investigators compared 200 women induced for isolated low amniotic fluid volume with 400 similar women with normal fluid volume and spontaneous labor onset. Women induced for low fluid volume were more likely to have cesareans (16% vs. 6%) and cesareans for nonreassuring fetal status (8% vs. 2%) without improving neonatal outcomes.
Manzanares S, Carrillo MP, Gonzalez-Peran E, et al. Isolated oligohydramnios in term pregnancy as an indication for induction of labor. J Matern Fetal Neonatal Med 2007;20(3):221-4.
And, of course, we also know that amniotic fluid volume is not fixed but varies according to maternal hydration.
Depressing, isn't it?
All Times America/New_York
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