December 14, 2009

Post term refusing IOL

A healthy 25-year-old nulliparous woman has an uncomplicated pregnancy at 42 weeks. Induction of labour is fully discussed, suggested and declined. Evaluate the tests that may be arranged to monitor fetal health until labour begins.

Where the advice over induction is unacceptable to the patient, various measures may be used to review fetal health. Several tests are described for this situation, but the problem remains that no test or group of tests has been shown to improve the perinatal outcome.

Fetal movement charts have long been used in late pregnancy as a form of fetal monitoring. They require the woman to note the time taken for 10 fetal movements. A large randomised-controlled trial (RCT), however, demonstrated no reduction in fetal mortality compared with the control group, and the use of these charts may increase anxiety without a beneficial effect. Various forms of fetal acoustic stimulation test have been developed using a transabdominal sound source and assessing the fetal reaction in terms of cardiotocograph (CTG) changes and fetal movements. Although such tests have the advantage of taking less time than other tests, there is no evidence for an improved perinatal outcome.

The standard non-stress test (NST) using a CTG relies on the observation of two or more episodes of fetal cardio acceleration of 15 beats or more occurring within 20 minutes of the onset of the test. It is generally thought, and advised by the National Institute for Health and Clinical Excellence (NICE), that twiceweekly tests should be performed, although the optimum scheme is not known. Furthermore, the NST used alone has a low sensitivity. The most common cause of perinatal death in such cases is meconium aspiration due to an acute asphyxial event, and the NST is not adequate to preclude such events. Contraction stress tests assessing fetal heart responses to oxytocic-induced contractions have largely gone out of use as the high false-positive rate has led to a high level of intervention. They also take longer and are more complicated to conduct than NSTs.

The assessment of liquor volume that may be related to placental function and fetal health has become an accepted part of surveillance of women such as this. A measurement of the amniotic fluid index of less than 5 cm or of the maximum vertical pocket depth of less than 2 cm (various other levels are quoted) suggest fetal compromise and lead to a recommendation for delivery. The biophysical profile combines an ultrasound assessment of fetal movements and tone, breathing movements and amniotic fluid volume. This combination would seem to be the most appropriate, but a recent RCT showed no advantage over CTG with amniotic depth measurement. Doppler studies of umbilical artery velocimetry have not been shown to be of benefit in predicting outcome.

There are clearly considerable limitations in the value of all these tests in detecting fetal compromise and enabling rescue, but NICE recommends twice-weekly CTG and measurement of amniotic pool depth, and this will remain the advice until further advice based on RCTs is available. The advice and its reasons must be discussed with this woman, and a sensitive approach is most likely to lead to a compromise, although there remains a possibility that the woman will wish for no tests and will await nature’s decision.

Simon G. Crocker Department of Obstetrics & Gynaecology Norfolk & Norwich University Hospital, Colney Lane, Norwich NR4 7UY, UK [OBSTETRICS, GYNAECOLOGY AND REPRODUCTIVE MEDICINE 17:1,2007 Published by Elsevier Ltd.]

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