Tocolytics are medicines that attempt to stop labor. They are used if labor begins before term. Tocolytics can stop labor or delay labor to give the baby's lungs time to mature. If started early in premature labor, they may be effective. They are not as successful later in labor, if the membranes have broken, or if your cervix is already dilated beyond 2 centimeters. When taking this medication, you may need hospitalization or home therapy.

Terbutaline, ritodrine, nifedipine and magnesium sulfate are all used as tocolytic drugs. Tocolytics are not used if the mother has chorioamnionitis (an infection in the membranes around the baby), abruptio placenta, severe preeclampsia or eclampsia, cardiac disease, or other severe medical illnesses. Tocolytics are also not used if the fetus has died in the uterus, or if the fetus is in acute distress. Some of these drugs are used in combination with other medications.

• Terbutaline: This medicine is used to stop preterm labor. It is also known as Brethine. It can be taken as a pill, through an IV (through a catheter directly into your vein), as an injection, or through a controlled infusion pump. A pump is used to give a continuous low dose of the terbutaline. Additional amounts of the medication can be administered if uterine activity increases. A subcutaneous (the medicine is injected under your skin but not directly into a vein) infusion pump may be used with home uterine monitoring. Some of the side effects can include nervousness, restlessness, insomnia, headache, rapid heart rate, nausea, hyperglycemia (high blood sugar) and hypokalemia (low blood potassium). A rare but serious side effect is pulmonary edema. The baby may also experience a fast heart rate and high or low blood sugar after birth. The mother and baby should be monitored while taking this drug. Your doctor should be informed if you have shortness of breath or chest pain while taking this medicine, or if the contractions begin again while you are on this medicine.

• Ritodrine: This medicine is used to stop preterm labor. It acts in a similar way to terbutaline. You can take it through an IV. The side effects are like those of terbutaline. If you have a history of cardiac dysrhythmias (irregular heart rhythms) or cardiac disease, hypertension or thyrotoxicosis (an excess of thyroid hormones), you should discuss this with your doctor before taking terbutaline or ritodrine.

• Nifedipine: This medicine is used to stop contractions. It is also called Adalat or Procardia and is taken as a pill. It is used to stop contractions and delay labor, and may also be used for occasional uterine irritability. Some of the side effects that may occur include facial flushing, headache, nausea, palpitations, and lightheadedness. No serious newborn side effects have been noted.

• Magnesium sulfate: This medicine can be used to stop contractions as well as in the treatment and prevention of seizures in a patient with preeclampsia. It can be taken as a pill or through an IV. Side effects may include feelings of extreme warmth, perspiration, flushing, nausea, vomiting, blurred vision, lightheadedness, lethargy, nasal stuffiness and constipation. Magnesium sulfate can affect your reflexes and slow your breathing. Some women report chest pain, especially if they are taking this medicine with another of the tocolytics. Women who have myasthenia gravis, a history of renal impairment (kidney problems), heart block, or a history of a myocardial infarction (heart attack) should discuss this with your doctor before using magnesium sulfate. Side effects usually go away within a few days. The fetus may show a decreased baseline heart rate. A newborn who has been exposed to magnesium sulfate may seem drowsy, have a weak cry and a decreased sucking rate in the early postpartum period. The mother and fetus should be monitored while on this medication.

• Indomethacin: This medicine is used to try to stop preterm labor, and is also called Indocin. It can be taken as a pill or as a suppository (in the rectum). Side effects include abdominal discomfort, nausea, vomiting, depression and dizzy spells for the mother. Indocin can also have serious effects on the fetus if used long term or if the gestational age is greater than 32-34 weeks. This drug may also be dangerous for the mother is she has a history of bleeding disorders, aspirin sensitivity, or kidney problems.

• Betamethasone: This medicine is a steroid used to help the fetal lungs develop more quickly. It is also called Celestone and is given as an injection into muscle tissue. The use of betamethasone can decrease the chance that the baby will have respiratory distress syndrome when born. It is usually used if preterm delivery is a concern. Sometimes doctors use dexamethasone, which is a very similar medicine. Side effects may include sleeplessness and higher blood sugar levels for the mother and decreased fetal movement for the baby.