We have little evidence that modern postdates management offers benefits
and considerable evidence that it does not. Randomized trials of expectant
management versus routine induction show few or no significant differences
in outcome. Attempts to prevent postdate pregnancy by membrane stripping or
nipple stimulation initiate labor more frequently compared with controls,
but studies present no data on delivery route. Vaginal application of
prostaglandin containing gel may ripen the cervix but has little effect on
cesarean rates. Macrosomia may be of concern because of increased
c-sections and birth injuries, but ultrasound predicts macrosomia poorly
(95% confidence intervals of +/- 20% with accuracy worst at extremes of
weight, and we have no evidence that induction improves outcomes. We do
know that performing cesareans for macrosomia does not decrease asphyxia or
injury rates.
Paradoxically, treatment works best on those who need it least: induction
is most likely to succeed when the fetus is healthy and the mother on the
verge of starting labor on her own. The inverse also holds: treatment does
least for those who most need it. Whether the process has gone awry or the
mother simply is not as far along as her doctor thinks, if her body is not
ready for labor, induction will likely fail. When testing reveals a
compromised fetus, doctors induce whether the cervix is ready or not.
Inducing an unripe cervix leads to long, hard labors, yet a baby in trouble
is least able to withstand the stress. Oligohydramnios, a complication of
postdates pregnancy, predisposes to abnormal fetal heart rate. When it is
found, obstetricians induce. Membranes will almost surely be ruptured for
one reason or another. Now the baby has no amniotic fluid.
We also have evidence that postdates management itself causes
complications, and, as with surveillance tests, this ironically reinforces
belief that postdatism is dangerous. Devoe and Sholl found that 30% of
fetuses testing normal developed fetal distress when labor was electively
induced, and the cesarean rate was 15% versus 2% for spontaneous labor.
Ahlden et al. found that the most likely scenario to end in an infected
baby was an overdue mother who was induced, had an amniotomy, internal
electronic fetal monitoring, many vaginal exams, and whose labor ended in
cesarean section. That so many healthy women carrying healthy term fetuses
had cesareans for fetal distress says more about management than the
dangers of 41-week gestations.
-Henci Goer, Obstetric Myths versus research Realities Bergin & Garvey 1995
Devoe LD and Sholl JS. Postdates pregnancy. Assessment of fetal risk and
obstetric management. J Reprod Med 1983;28(9).
Ahlden S et al. Prediction of sepsis neonatorum following a full-term
pregnancy. Gynecol Obstet Invest 1988;70(1).
Reprinted from Midwifery Today E-News (Vol 2 Issue 9 March 3, 2000)
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