A contraction stress test (CST) is performed near the end of

pregnancy Pregnancy is the time during which one or more offspring develops ( gestates) inside a woman's uterus (womb). A multiple pregnancy involves more than one offspring, such as with twins. Pregnancy usually occurs by sexual intercourse, but ...

(34 weeks' gestation) to determine how well the

fetus A fetus or foetus (; plural fetuses, feti, foetuses, or foeti) is the unborn offspring that develops from an animal embryo. Following embryonic development the fetal stage of development takes place. In human prenatal development, fetal develo ...

will cope with the contractions of

childbirth Childbirth, also known as labour and delivery, is the ending of pregnancy where one or more babies exits the internal environment of the mother via vaginal delivery or caesarean section. In 2019, there were about 140.11 million births glo ...

. The aim is to induce contractions and monitor the

to check for

heart rate Heart rate (or pulse rate) is the frequency of the heartbeat measured by the number of contractions (beats) of the heart per minute (bpm). The heart rate can vary according to the body's physical needs, including the need to absorb oxygen and e ...

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 A fetus or foetus (; plural fetuses, feti, foetuses, or foeti) is the unborn offspring that develops from an animal embryo. Following embryonic development the fetal stage of development takes place. In human prenatal development, fetal develo ...

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 and is a contraindication to labor. Patient's obstetricians usually consider operative delivery in such situations.

Contraindications

This "stress test" is usually not performed if there are any signs of

premature birth Preterm birth, also known as premature birth, is the birth of a baby at fewer than 37 weeks gestational age, as opposed to full-term delivery at approximately 40 weeks. Extreme preterm is less than 28 weeks, very early preterm birth is betwee ...

, placenta praevia, vasa praevia, cervical incompetence, multiple gestation, previous classic caesarian section. Other contraindications include but are not limited to previous uterine incision with scarring, previous myomectomy entering the uterine cavity, and PROM. Any contraindication to labor is contraindication to CST.

Procedure

CST is performed weekly, as the fetus is assumed to be healthy after a negative test and should remain so for another week. This test is done in hospital or clinic setting. External fetal monitors are put in place and then either nipple stimulation or IV

pitocin Synthetic oxytocin, sold under the brand name Pitocin among others, is a medication made from the peptide ''oxytocin''. As a medication, it is used to cause contraction of the uterus to start labor, increase the speed of labor, and to st ...

(oxytocin) is used to stimulate uterine contractions.

Nipple stimulation

This is a procedure that relies on endogenous release of

oxytocin Oxytocin (Oxt or OT) is a peptide hormone and neuropeptide normally produced in the hypothalamus and released by the posterior pituitary. It plays a role in social bonding, reproduction, childbirth, and the period after childbirth. Oxytoci ...

following nipple stimulation, and is conducted by the patient. The

nurse Nursing is a profession within the health care sector focused on the care of individuals, families, and communities so they may attain, maintain, or recover optimal health and quality of life. Nurses may be differentiated from other health ...

instructs the patient on the procedure, as follows. One nipple is massaged gently through clothing until a contraction begins, or for a maximum of 2 minutes. If at least 3 contractions in 10 minutes is not achieved, then the patient rests for 5 minutes and the other nipple is stimulated.American College of Obstetricians and Gynecologists (ACOG). (1999). Antepartum fetal surveillance (Practice Bulletin No. 9). Washington, DC: Author.

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

to the pregnant woman. The target is to achieve around three contractions every ten minutes.

Interpretation

History

The CST was the first antenatal surveillance test that was developed after the development of the cardiotocograph. The oxytocin challenge test was first described in 1972 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.

References

External links

Contraction Stress Test
at webmd.com {{Pregnancy Tests during pregnancy