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MS WordPerinatologist Corner - C.E.U/C.M.E. Modules
Post-term Pregnancy and Induction of Labor
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5 Antenatal Fetal Surveillance
Despite the common use of non-stress testing, amniotic fluid volume assessment, and the biophysical profile, there is little evidence from randomized, controlled trials that antepartum fetal testing in post-term pregnancies improves outcome.
There is observational data that the non-stress test has a high false positive rate of approximately 75%, and also as high as a 1.4-2.7% false negative rate, if fetal demise is the outcome variable. The risk of perinatal death with a reactive non-stress test is still1-3/1000 in the next 7 days. (Evertson et al)
Non-reactive non-stress tests should be repeated and/or followed up with a biophysical profile (Manning et al) or a contraction stress test. (Freeman et al I) (Freeman et al II) Both of the latter retain higher false positive rates of about 45% each, but have lower false negative rates of 0.4-0.7%. (The risk of perinatal mortality is predicted to be <1/1000 in the next 3-7 days).
These data were accumulated in patients at all gestational ages, with many different underlying high-risk conditions, and may not be specifically applicable to post-term fetuses. As noted above, these strategies also were implemented without comparing a group that underwent testing to one not being tested in the setting of a randomized controlled trial.
Expert opinion recommends that biophysical scores <6 be repeated within 24 hours, and/or, should prompt delivery at this gestational age. Comparing the full biophysical profile to the “modified biophysical” (NST plus single deepest pocket of amniotic fluid >2 cm) showed no advantage to using the full profile.
The amniotic fluid index is subject to both inter- and intra-observer variability, and is associated with increased intervention rates, but not necessarily with improved outcomes. Nevertheless, marked oligohydramnios (AFI< 5.0) remains clinically worrisome.
Unlike the situation with growth restricted fetuses, Doppler velocimetry has not proved helpful for the management of the post-dates fetus.
There is also no evidence relevant to the appropriate frequency of testing, nor is there evidence that one form of antenatal surveillance is superior to any other. Nevertheless, in the presence of an unfavorable cervix, antenatal testing is a frequently employed strategy for the management of post-term patients.
