A contraction stress test (CST) is performed near the end of pregnancy (34 weeks' gestation) to determine how well the fetus will cope with the contractions of childbirth. The aim is to induce contractions and monitor the fetus to check for heart rate abnormalities using a cardiotocograph. A CST is one type of antenatal fetal surveillance technique.

During uterine contractions, fetal oxygenation is worsened. Late decelerations in fetal heart rate occurring during uterine contractions are associated with increased fetal death rate, growth retardation and neonatal depression. This test assesses fetal heart rate in response to uterine contractions via electronic fetal monitoring. Uterine activity is monitored by tocodynamometer.

Medical uses

The CST is used for its high negative predictive value. A negative result is highly predictive of fetal wellbeing and tolerance of labor. The test has a poor positive predictive value with false-positive results in as many as 30% of cases. A positive CST indicates high risk of fetal death due to hypoxia

Contraindications

This "stress test" is usually not performed if there are any signs of premature birth, placenta praevia, vasa praevia, cervical incompetence, multiple gestation, previous classic caesarian section. This test is done in hospital or clinic setting.

Oxytocin challenge test (OCT)

If adequate contractions (at least 3 in 10 minutes) cannot be achieved with nipple stimulation, an oxytocin challenge test may be performed. It involves the intravenous administration of exogenous oxytocin to the pregnant woman. The target is to achieve around three contractions every ten minutes.

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| Negative|| No late or significant variable decelerations,

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| Equivocal—Suspicious|| Presence of late decelerations with fewer than 50% of contractions or significant variable decelerations. Requires repeat testing on following day. and was standardised in 1975 when the parameters of contraction number and frequency were given.

Historically, a CST was done after a non reactive NST. Today, a biophysical profile (BPP) is usually performed.

See also

  • Nonstress test
  • Cardiotocography

References

  • Contraction Stress Test at webmd.com