sobre o CTG

Electronic fetal heart rate monitoring is used during pregnancy in the surveillance of high-risk pregnancies, and also during labour. Its use is normally limited to institutional births.
The monitoring is most commonly achieved by an external Doppler ultrasound ransducer, or by an internal (vaginal) electrode attached to the fetal scalp, after rupture of the membranes. Although the information on fetal heart rate is more accurate in the latter method than with auscultation, the interpretation is difficult; the tracings are often interpreted differently by different care-givers, and even by the same people at different times (Cohen et al 1982, Van Geijn 1987, Nielsen et al 1987).
The sensitivity of the method with respect to the detection of fetal distress is high, but the specificity is low (Grant 1989). This means that the method results in a high rate of false positive signals, and a concomitant high number of (unnecessary) interventions, especially if used in a group of low-risk pregnant women (Curzen et al 1984, Borthen et al 1989). In high-risk pregnancies and in high-risk cases during labour the method has proven to be useful and may, in addition, offer reassurance to the woman, although its use inevitably limits the woman's capacity to move about as she wishes.

Do mesmo estudo da OMS - aqui.