Tocolytics In Pregnancy

4 min read


What are Tocolytics?

Tocolytics are the drugs used to suppress initiation of premature labour. Derived from the Greek ‘tokos’ which means childbirth and ‘lytic’ which implies capable of dissolving, tocolytics are also called labor repressant drugs or anti-contraction medications. These drugs are mostly given to avoid and postpone premature delivery of a baby. The therapy is used to buy time for a day or two for the administration of betamethasone, a glucocorticoid drug which greatly accelerates fetal lung maturity, so that the baby can breathe on her own even after preterm birth.
The inhibition of uterine contractions is partial and tocolytic medications can postpone the birth for a few days at the maximum. However, they are not always very effective and sometimes delay the birth by only a day or so. Strict monitoring of blood pressure, fetal movements, etc is required while using tocolytic drugs.

Diagnosis of Preterm Labor and Tocolytics

The most reliable and correct diagnosis of preterm labor is based on clinical symptoms which are sometimes imperfect as preterm labor subsides in 30 percent of patients. The most reliable markers of preterm labor are painful continuous uterine contractions accompanied by softening, dilatation and effacement of cervix. Cervical effacement is the thinning out of cervix.
Tocolytics medications inhibit or suppress the contractions of myometrium. This is the prime focus of preterm labor. Tocolytics helps in delaying the preterm birth and prevents maternal and fetal risks as far as possible. During this delay, antenatal corticosteroids can be administered to lower the risk of respiratory distress sin neonates. The commonly used corticosteroids are betamethasones, dexamethasones and should be given at least 18 hours before the preterm birth.
Antenatal corticosteroids reduce the neonatal morbidities (intraventricular hemorrhage and necrotizing enterocolitis).

Tocolytics in Pregnancy

Tocolytics medications should not be taken before 17-20 weeks of pregnancy to treat preterm labor. Some doctors prescribe tocolytics post completion of 34 weeks of pregnancy while others wait till the 36th week. Different agents of tocolytics are prescribed by doctors after assessing the risks and the benefits.
Tocolytic medications have been available since ages but the knowledge about their role in suppression of preterm labor is recently known. Preterm delivery is defined as delivery occurring before 37 weeks of gestation.

Causes Of Preterm Labor

The true cause of premature labor is not clear. It is believed that the preterm activation of physiological contracting process or pathological factor accountable for uterine contractions can result in preterm delivery.
A compilation of factors consisting of stretching and over-distension of myometrial and fetal membranes, activation of placenta, decidual hemorrhage, fetal placental hypothalamic-pituitary-adrenal axis, and inflammation or infection of uterus are responsible for preterm births. Preterm births are also common in elderly pregnant women, increased usage of assisted reproductive techniques, rising ratio of multiple gestations, increased awareness of physicians to maternal health, etc.
Tocolytics in Pregnancy

Treatment of Preterm Labor with Toclytic Agents

The tocolytic drugs can slow down contractions. Following classes of tocolytic agents are widely available:

  • beta-mimetics (such as terbutaline)
  • magnesium sulfate
  • calcium channel blockers (such as nifedipine) and
  • non-steroidal anti-inflammatory drugs or NSAIDs (such as indomethacin)

In some hospitals terbutaline is used to females having low risk of preterm labor and preterm birth while magnesium sulfate is the drug of choice in women having higher risk of preterm labor.
Along with tocolytic medications, bed rest, pain killers, extra fluids, adequate screening should be done as the first and primary step.In case the contractions do not subside, tocolytic medications may be continued depending on the risk measurement of having a preterm delivery. Transvaginal ultrasound and fetal fibronectin test can help you determine the risk of preterm delivery.
If the doctor decides to continue with tocolytics, the choice and dosage of tocolytic drug is based upon the age of the baby and the condition of baby’s lungs.

When Should You Not Use Tocolytics Medications?

Do not use these medications under following conditions of your pregnancy:

  • If fetus is more than 34 weeks gestation
  • If fetus is less than 2500 grams or if it has placental insufficiency or IUGR (intrauterine growth restriction)
  • If fatal chromosomal or congenital abnormalities are present
  • If cervical dilatation is more than 6 centimeters
  • If intrauterine infection or chorioamnionitis is present
  • If fetal distress is present or suspected
  • If mother has eclampsia, preeclampsia, pregnancy induced hypertension (PIH), vaginal bleeding, abruptio placenta, cardiac ailment, etc.
  • The baby has an abnormal heart rate
  • If the baby has a slow growth rate
Side Effects Of Tocolytics
  1. Beta-Adrenergic receptor-agonists (Terbutaline)
    Hypotension, tachycardia, shortness of breath, chest pain, pulmonary edema, hypokalemia, hyperglycemia etc have been noted as side effects of tocolytic agent Terbutaline
  2. Magnisium Sulphate
    When magnesium sulphate is used as a tocolytic agent, it can cause the pregnant woman to suffer from nausea, flusing, headache, lethargy, and hypotension
  3. Nitric Oxide Donors (nitroglycerin)
    This labor repressant can cause flushing, tachycardia, hypotension and headache and worsening of dependent cardiac lesions
  4. Calcium Channel Blockers (Nifedipine)
    Dizziness, flushing, hypotension are the side effects of using Nifedipine. However, if used with magnesium sulfate, it can supress the heart rate, decrease contractility, cause increase in hepatic enzyme levels
  5. Cyclooxygenase Inhibitors (Indomethacin)
    Nausea, GERD, gastritis, platelet dysfunction are all the side effects of Indomethacin
  6. Oxytocin-receptor antagonists
    Hypersensitivity reactions and probable increase in the fetal death

Tocolytic medicines should be used only if the risks are lesser than the benefits. If the baby has died in the womb, of has some fatal abnormality which can cause death after delivery, tocolytics should not be used.

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