Contraction stress test
Encyclopedia
A contraction stress test (CST) is performed near the end of pregnancy
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
.
release of oxytocin
following nipple
stimulation, and is conducted by the patient. The nurse 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.
oxytocin
to the pregnant woman. The target is to achieve around three contractions every ten minutes.
*Negative: no late or significant variable decelerations
*Equivocal—Suspicious: presence of late decelerations with fewer than 50% of contractions) or significant variable decelerations
*Equivocal—Tachysystole: Presence of contractions that occur more frequently than every 2 minutes or last longer than 90 seconds in the presence of late decelerations
*Equivocal—Unsatisfactory: Fewer than three contractions occur within 10 minutes, or a tracing quality that cannot be interpreted
. A negative result is highly predictive of fetal wellbeing and tolerance of labor. The test has a poor positive predictive value
with false-posiive results in as many as 30% of cases.
Historically, a CST was done after a non reactive NST
. Today, a biophysical profile (BPP)
is usually performed.
or placenta praevia
.
Other contraindications include but are not limited to previous uterine incision with scarring, previous myomectomy
entering the uterine cavity, PROM and incompetent cervix.
Pregnancy
Pregnancy refers to the fertilization and development of one or more offspring, known as a fetus or embryo, in a woman's uterus. In a pregnancy, there can be multiple gestations, as in the case of twins or triplets...
to determine how well the fetus
Fetus
A fetus is a developing mammal or other viviparous vertebrate after the embryonic stage and before birth.In humans, the fetal stage of prenatal development starts at the beginning of the 11th week in gestational age, which is the 9th week after fertilization.-Etymology and spelling variations:The...
will cope with the contractions
Contraction (childbirth)
-Throughout menstrual cycle:The uterus frequently contracts throughout the entire menstrual cycle, and these contractions have been termed endometrial waves or contractile waves. These appear to involve only the sub-endometrial layer of the myometrium...
of childbirth
Childbirth
Childbirth is the culmination of a human pregnancy or gestation period with the birth of one or more newborn infants from a woman's uterus...
. The aim is to induce contractions and monitor the fetus
Fetus
A fetus is a developing mammal or other viviparous vertebrate after the embryonic stage and before birth.In humans, the fetal stage of prenatal development starts at the beginning of the 11th week in gestational age, which is the 9th week after fertilization.-Etymology and spelling variations:The...
to check for heart rate
Heart rate
Heart rate is the number of heartbeats per unit of time, typically expressed as beats per minute . Heart rate can vary as the body's need to absorb oxygen and excrete carbon dioxide changes, such as during exercise or sleep....
abnormalities using a cardiotocograph
Cardiotocography
In medicine , cardiotocography is a technical means of recording the fetal heartbeat and the uterine contractions during pregnancy, typically in the third trimester...
.
Nipple Stimulation
This is a procedure that relies on endogenousEndogenous
Endogenous substances are those that originate from within an organism, tissue, or cell. Endogenous retroviruses are caused by ancient infections of germ cells in humans, mammals and other vertebrates...
release of oxytocin
Oxytocin
Oxytocin is a mammalian hormone that acts primarily as a neuromodulator in the brain.Oxytocin is best known for its roles in sexual reproduction, in particular during and after childbirth...
following nipple
Nipple
In its most general form, a nipple is a structure from which a fluid emanates. More specifically, it is the projection on the breasts or udder of a mammal by which breast milk is delivered to a mother's young. In this sense, it is often called a teat, especially when referring to non-humans, and...
stimulation, and is conducted by the patient. The nurse 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.
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 exogenousExogenous
Exogenous refers to an action or object coming from outside a system. It is the opposite of endogenous, something generated from within the system....
oxytocin
Oxytocin
Oxytocin is a mammalian hormone that acts primarily as a neuromodulator in the brain.Oxytocin is best known for its roles in sexual reproduction, in particular during and after childbirth...
to the pregnant woman. The target is to achieve around three contractions every ten minutes.
Interpretation
*Positive: presence of late decelerations with at least 50% of the contractions*Negative: no late or significant variable decelerations
*Equivocal—Suspicious: presence of late decelerations with fewer than 50% of contractions) or significant variable decelerations
*Equivocal—Tachysystole: Presence of contractions that occur more frequently than every 2 minutes or last longer than 90 seconds in the presence of late decelerations
*Equivocal—Unsatisfactory: Fewer than three contractions occur within 10 minutes, or a tracing quality that cannot be interpreted
Results & Efficacy
The CST is used for its high negative predictive valueNegative predictive value
In statistics and diagnostic testing, the negative predictive value is a summary statistic used to describe the performance of a diagnostic testing procedure. It is defined as the proportion of subjects with a negative test result who are correctly diagnosed. A high NPV means that when the test...
. A negative result is highly predictive of fetal wellbeing and tolerance of labor. The test has a poor positive predictive value
Positive predictive value
In statistics and diagnostic testing, the positive predictive value, or precision rate is the proportion of subjects with positive test results who are correctly diagnosed. It is a critical measure of the performance of a diagnostic method, as it reflects the probability that a positive test...
with false-posiive results in as many as 30% of cases.
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
Nonstress test
A nonstress test is a screening test used in pregnancy. A cardiotocograph is used to monitor the fetal heart rate.-Premise:The premise of the NST is that a well-oxygenated, non-acidemic fetus will spontaneously have temporary increases in the fetal heart rate...
. Today, a biophysical profile (BPP)
Biophysical profile
A biophysical profile is a prenatal ultrasound evaluation of fetal well-being, involving a scoring system. It is often done when a non-stress test is non reactive, or for other obstetrical indications.-The test:...
is usually performed.
Contraindications
This "stress test" is usually not performed if there are any signs of premature birthPremature birth
In humans preterm birth refers to the birth of a baby of less than 37 weeks gestational age. The cause for preterm birth is in many situations elusive and unknown; many factors appear to be associated with the development of preterm birth, making the reduction of preterm birth a challenging...
or placenta praevia
Placenta praevia
Placenta praevia is an obstetric complication in which the placenta is attached to the uterine wall close to or covering the cervix. It can sometimes occur in the later part of the first trimester, but usually during the second or third. It is a leading cause of antepartum haemorrhage...
.
Other contraindications include but are not limited to previous uterine incision with scarring, previous myomectomy
Myomectomy
Myomectomy, sometimes also fibroidectomy, refers to the surgical removal of uterine leiomyomas, also known as fibroids. In contrast to a hysterectomy the uterus remains preserved and the woman retains her reproductive potential.-Indications:...
entering the uterine cavity, PROM and incompetent cervix.
External links
- Contraction Stress Test at webmd.com