What is a Tocolytic?

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  • Written By: Rolando Braza
  • Edited By: Melissa Wiley
  • Last Modified Date: 22 November 2019
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A tocolytic is a drug given to a pregnant woman to delay preterm labor. The delay will allow the administration of steroid hormones like glucocorticoids to develop the lungs and reduce the chance of respiratory distress syndrome in a neonate. The delay in preterm labor can also reduce the likelihood of the baby's death, especially if the preterm labor occurs before the 34th week of the mother’s pregnancy. A tocolytic can defer preterm labor for a maximum of 48 hours — enough time to transfer the pregnant woman to a health care facility that can handle the care of a preterm baby.

A doctor normally performs tests to confirm a diagnosis of preterm labor prior to initiating tocolytic treatment. He or she checks to see if the cervical length has reached approximately 0.71 inches (18 mm). The doctor will also check for the presence of fibronectin, an indicator that the pregnant woman is about to give birth.

The use of a tocolytic must be exercised with care, ensuring that the benefits of its use outweigh the risks. In general, a tocolytic is employed between the 24th and 34th month of pregnancy. Neonatal and maternal risks are low at this gestation period. Tocolytic drugs include indomethacine, nifedipine, and magnesium sulfate.


Indomethacine is prepared in pill and suppository form. Its side effects include dizziness, vomiting, and nausea. It is not advisable for use by pregnant women who have kidney disorders or are known to be bleeders. The long-term use of this drug requires caution because it can have ill effects on the baby such as jaundice, pulmonary hypertension, and renal problems.

Nifedipine comes in the form of a pill. Some of its side effects are palpitations, headaches, and lightheadedness. One of the benefits in using this drug agent is the reduction of polyhydramnios, a condition in which there is excessive amniotic fluid.

Magnesium sulfate can be taken in pill form or dispensed via an intravenous (IV) line. Perspiration, nausea, and constipation are some of its side effects. This drug can easily reach the placenta and cause the baby to have respiratory and motor depression. To avoid risk of toxicity, some doctors recommend that a maternal-fetal-medicine (MFM) specialist, also called a perinatologist, be consulted before prolonged use of this drug beyond 72 hours.

A pregnant woman known to have heart disease, pulmonary disease, or renal failure is advised to be seen by an MFM specialist for proper assessment of risks before being given tocolytic medication. She should be precluded from taking tocolytics when there are contraindications such as remarkable vaginal bleeding, allergies, or oligohydramnios — a condition in which there is a deficiency in amniotic fluid. Tocolytic medication must always be taken under the guidance of a doctor for proper administration and to avoid further preterm labor complications and to obtain the best therapy results.


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