When and how should a contraction stress test be performed in a pregnant woman at ≥34 weeks gestation?

Contraction Stress Test (CST)

The contraction stress test is largely obsolete in modern obstetric practice at ≥34 weeks gestation and should not be routinely performed; instead, use cardiotocography (NST) combined with umbilical artery Doppler assessment for fetal surveillance.

Why CST Is No Longer Recommended

The provided guidelines from the Society for Maternal-Fetal Medicine (2020) and ACR (2016) make no mention of contraction stress testing in their comprehensive recommendations for fetal well-being assessment 1. This represents a significant shift from historical practice, as CST was the original "gold standard" for fetal surveillance in the 1970s 2.

Modern fetal surveillance has replaced CST with:

• Non-stress testing (NST/cardiotocography) - the primary method
• Umbilical artery Doppler assessment - for high-risk conditions
• Biophysical profile (BPP) or modified BPP - combining NST with amniotic fluid assessment

Current Evidence-Based Approach at ≥34 Weeks

For Routine High-Risk Surveillance

Use weekly cardiotocography (NST) as the primary surveillance method 1. The NST is:

• Reactive when ≥2 fetal heart rate accelerations occur in 20 minutes (15 bpm above baseline for 15 seconds at ≥32 weeks)
• Nonreactive if after 40 minutes there is ≤1 acceleration 3

For Fetal Growth Restriction

Implement weekly cardiotocography for FGR without absent/reversed end-diastolic velocity, increasing frequency with complications 1 (GRADE 2C).

For Severe Compromise

With reversed end-diastolic velocity, perform cardiotocography at least 1-2 times per day 1 (GRADE 2C).

Historical Context of CST

While CST was effective historically—showing no antepartum fetal deaths in post-term pregnancies 4 and reliable negative predictive value 5, 6—it had significant limitations:

• Labor-intensive: Required 1-3 hours of oxytocin infusion or 40-60 minutes of breast stimulation 2, 7
• Contraindications: Not applicable to many high-risk pregnancies 2
• High false-positive rate: 39% abnormal CST rate in post-term pregnancies, yet only 5.4% required intervention 5

Practical Algorithm for ≥34 Weeks

1. Start with NST - perform weekly for most high-risk conditions
2. Add umbilical artery Doppler if FGR suspected or confirmed
3. Consider modified BPP (NST + amniotic fluid assessment) for comprehensive evaluation 3
4. Escalate frequency based on Doppler findings and clinical scenario

Key Pitfall to Avoid

Do not order CST based on outdated protocols or older textbooks. The test has been superseded by less invasive, equally effective methods that don't carry risks of inducing labor or require the time commitment and contraindication considerations of CST.