It is a test that helps us observe the course of the baby's heartbeat and the relationship of the heartbeat with the baby's movements and contractions, if any. Based on this observation, it is tried to understand whether the fetus is normal or in distress. NST is one of the tests performed to determine the well-being of the fetus. Other tests performed to determine the well-being of the fetus are ultrasound, measurement of amniotic fluid, Doppler measurements, biophysical profile, and OCT.
It has two ends, called props, which are fixed on the pregnant woman's abdomen. One of the probes detects uterine contractions and the other detects the baby's heart sounds. Detected contractions and heart sounds are transferred by the device onto a graph paper. It is necessary for the mother to lie on her left side during the test, as it will increase blood flow to the uterus.
During this process, which takes approximately 20 minutes, pregnant women are asked to press a small button given to them whenever they feel the baby's movements. In this way, the baby's heart rate and reactivity (variations in beat rate), contractions in the uterus and the responses of the baby's heart to these contractions are evaluated by the physician and indirect information about the baby's health is obtained.
Risk. In pregnancies that do not occur, it is recommended to repeat NST application once a week after the 36th week of pregnancy and every 2-3 days after the 40th week of pregnancy. It is recommended that the mother be full by eating a carbohydrate-rich diet before the NST procedure. NST is not performed in fetuses younger than 28 weeks because the fetus is not yet developed enough to give such reactions. The fact that the fetus is asleep may also make the test falsely negative.
Situations in which the well-being of the fetus should be evaluated by NST or other methods:
- Less sensation of fetal movements.
- Premature rupture of membranes (early water breaking)
- Too much or too little amniotic fluid
- IUGR (Fetal growth retardation)
- Diarrhea
- Isoimmunization (Blood incompatibility)
- Fetal anomalies
- Multiple pregnancies
- Abnormal or irregular fetal heartbeats
- Hypertension
- Diabetes
- Kidney diseases
- Collogen tissue diseases
- Heart diseases ailments
- Thyrotoxicosis (Imbalance in goiter tests)
- Hemoglobinopathies
- Anemia
As in all tests Like NST, there are margins of error. NST being reactive (with good results) is a more reliable finding than being nonreactive (with bad results). When NST results are reactive, that is, good, the reliability is 95%, meaning the fetus is really in good condition with a 95% probability. However, when NST gives non-reactive, that is, bad results, the rate of the fetus being in a really bad situation (distress, fetal distress) is 40%.
REACTIVE NST
NST If there are at least two accelerations of 15 beats and 15 seconds in the fetal heart rate during 20 minutes, this test is considered reactive, that is, good. If the fetal heart rate does not accelerate twice within 20 minutes, the test is extended to 40 minutes. If the fetal heart rate does not accelerate twice in this second 20 minutes, the test is considered non-reactive, that is, bad. Considering the NST result as reactive, that is, good, indicates that the fetus will most likely be in good condition for 1 week.
NON-REACTIVE NST
As explained above, non-reactive, that is, As a result of a test that is determined to be bad, it cannot be said that the fetus is definitely in a bad or distressed condition. Non-reactive NST has low reliability. Therefore, the fetus is re-evaluated with further tests. For this purpose, tests such as contraction stress test (CST, OCT), biophysical profile, doppler, ultrasound are used.
DECELERATIVE NST
Detected in the fetal heartbeat in the NST chart. are slowdowns. It suggests that the fetus may be in a state of distress (fetal distress). There are three types of deceleration: early deceleration, late deceleration and variable deceleration. Early decelerations are decelerations that occur just before the contractions (contractions in the uterus) observed in NST and occur as a result of compression of the fetus's head. They are insignificant decelerations and do not mean that the fetus is in distress. Variable decelerations occur independently of contractions and are the result of cord compression, so they are important decelerations. Late decelerations occur immediately after contractions and are caused by placental insufficiency. These indicate that the fetus is in distress (fetal distress). In cases where decelerations are very severe, an emergency cesarean section may be required.
FETAL TACHYCARDIA
The fetal heart rate is above 160/min on the NST chart. Between 160-180 is called mild tachycardia, between 180-200 is called moderate, and above 200 is called severe tachycardia.
Treatment is planned according to the cause.
Reasons:
- Fetal hypoxia, fetal distress (state of distress in the fetus)
- High fever in the mother
- Hyperthyroidism
- Anemia in the mother and fetus
- Drugs with parasympatholytic effect: Ex: Atropine, hydroxyzine
- Drugs with sympathomimetic effect: Ritodrine, terbutaline (These are drugs given to stop premature birth.)
- Chorioamnionitis (Inflammation of pregnancy membranes inflammation)
- Fetal heart failure or another cardiac pathology
- Prematurity
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