Contraction Stress Test (CST) - Gynecology

What is a Contraction Stress Test (CST)?

A Contraction Stress Test (CST) is a prenatal test used to evaluate the well-being of the fetus by observing its heart rate response to uterine contractions. This test helps determine whether the baby can handle the stress of labor and if the placenta is providing adequate oxygen to the fetus.

When is CST Performed?

CST is typically performed in the third trimester of pregnancy, particularly if there are concerns about the baby's health. Indications for CST include high-risk pregnancies, such as those involving gestational diabetes, hypertension, or a history of complications in previous pregnancies. It may also be recommended if non-stress test (NST) results are non-reassuring or if there is decreased fetal movement.

How is CST Conducted?

The test involves stimulating contractions, either naturally or through medication. This can be achieved by:

Nipple Stimulation: Encouraging contractions by massaging the nipples.
Oxytocin: Administering a synthetic form of the hormone oxytocin via an intravenous (IV) line to induce contractions.

During the test, the fetal heart rate is monitored using an external fetal monitor. The healthcare provider observes the baby's heart rate response to the contractions.

What Do the Results Indicate?

The results of a CST can be classified as:

Negative CST: No significant decelerations in the fetal heart rate during contractions. This is a reassuring sign indicating the baby is likely to tolerate labor well.
Positive CST: Late decelerations in the fetal heart rate with more than half of the contractions. This may indicate the baby is under stress and cannot tolerate labor well, potentially leading to further interventions.
Equivocal CST: Results are unclear or there are intermittent decelerations. Further testing may be required.

What are the Risks Associated with CST?

While the CST is generally safe, it does carry some risks, including:

Premature Labor: The induced contractions could potentially lead to premature labor.
Discomfort or pain from contractions.
Possible need for additional monitoring or intervention if the test results are concerning.

It is essential to discuss the potential risks and benefits with your healthcare provider before undergoing the test.

Alternatives to CST

Other tests may be used to assess fetal well-being, including:

Non-Stress Test (NST): Measures fetal heart rate in response to fetal movements without inducing contractions.
Biophysical Profile (BPP): Combines an ultrasound with an NST to assess fetal health.
Doppler Ultrasound: Evaluates blood flow in the umbilical artery and other fetal vessels.

These alternatives may be considered if CST is deemed inappropriate or if additional information is needed.

Preparing for a CST

Before undergoing a CST, it is crucial to follow the healthcare provider's instructions, which may include:

Ensuring you are well-hydrated.
Avoiding heavy meals before the test.
Wearing comfortable clothing and bringing any necessary medical records.

It is also important to communicate any concerns or questions with your healthcare provider to ensure you are fully informed and prepared.

Conclusion

The Contraction Stress Test (CST) is a valuable tool in prenatal care to assess the fetus's ability to handle the stress of labor. Understanding the procedure, its indications, and potential risks can help expectant mothers make informed decisions about their care. Always consult with your healthcare provider to determine the best approach for monitoring your baby's health.