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Antenatal Fetal Surveillance (AFS)

A wide range of tests of fetal well being have been introduced during the last thirty years. Both "BIOCHEMICALTESTS" and "BIOPHYSICAL METHODS OF MONITORING" have the theoretical ability to detect changes in fetal well being that may occur over hours, days or weeks. Antenatal monitoring is useful due to two reasons: Firstly: these methods can detect or predict fetal compromise; Secondly: with appropriate interpretation and action they can reduce the frequency or severity of adverse perinatal events of needless intervention. Apart from the clinical methods and biochemical tests there are biophysical methods which have almost completely replaced biochemical tests: These tests include:

  • Non stress test
  • Contraction stress test
  • Fetal Biophysical profile
  • Vibroacoustic stimulation test
  • Modified biophysical profile
  • Umbilical and uterine Doppler ultrasound.

The most commonly applied method-NST-is described below.

Non-Stress Test

The evaluation of Fetal heart Rate patterns (without the added stress of induced contractions) has been widely incorporated into antenatal care for both screening and diagnosis. It is an assessment of immediate fetal condition.

The rationale underlying this is that the presence of spontaneous fetal heart rate accelerations associated with fetal movements (FETAL REACTIVITY) is an indicator of fetal well being and vice versa. A REACTIVE TEST is present when two or more fetal heart rate accelerations are clearly recorded during a 20 minute period, each acceleration of 15 or more beats per minute and lasting 15 or more seconds, usually occurring simultaneously with episodes of fetal activity. NST has high frequency of false positive results (n50-80 per cent). False negative rate is only 3.2 per 1000, so the likelihood of fetal death or serious fetal morbidity following a negative (reactive test is extremely low.

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