Non-steroidal anti-inflammatory drugs, or NSAIDs, include ibuprofen (Motrin) and indomethacin (Indocin). Indomethacin is the most frequently used NSAID for preterm labor. It can be given by mouth or by rectal suppository. It can be used alone or in combination with other tocolytics, like magnesium sulfate.

Indomethacin is particularly effective in the second and early third trimesters, and it may be useful in women who continue to have contractions after being given magnesium sulfate. In most circumstances, indomethacin should not be used for more than two to three days at a time.

How Does Indomethacin Work?

NSAIDs keep the body from making prostoglandins, substances which cause uterine contractions.

How Effective Is Indomethacin?

Indomethacin can reduce the number and frequency of contractions; however, this effect and how long it lasts varies from woman to woman. Like all tocolytic medications, however, indomethacin does not consistently prevent or delay preterm delivery for a significant period of time.

Even so, studies have shown that indomethacin can delay delivery for at least several days (depending on how far dilated a woman's cervix is when the medication is started). This isn't a lot of time, but it can make a big difference for the baby if the mother is given steroids along with indomethacin. After 48 hours, steroids improve a baby's lung function and reduce his or her risk of dying by 40%.

What Are the Possible Side Effects of Indomethacin?

For the Mother

Indomethacin causes indigestion in many women. This effect may be lessened by taking indomethacin with food or, if necessary, by also taking an antacid.

For the Baby

Indomethacin has two potentially serious side effects for the fetus. This drug can cause (1) a reduction in the amount of urine the fetus produces and (2) changes in the way the blood circulates through the fetus's body.

If the fetus makes less urine, the amount of amniotic fluid in the uterus may also be reduced, a condition known as oligohydramnios. The reduction in fluid seems to be most common when a mother is on indomethacin for more than two days. During this time, amniotic fluid levels should be checked regularly by ultrasound (a machine that uses sound waves to produce a picture of the inside of the body). Fortunately, the amount of amniotic fluid almost always returns to normal once indomethacin is discontinued.

Indomethacin can also cause a major blood vessel, the ductus arteriosus, to close prematurely. This can cause serious problems after the baby is born. Fortunately, the ductus does not close early if indomethacin is used for less than 48 hours. It's also less likely to be a problem before 32 weeks of pregnancy. If a mother takes the medicine for more than 2 days, it is useful to check an ultrasound of the baby's heart to make sure this blood vessel has not been affected.

Other side effects in the baby have been reported, but none have been consistently confirmed.

Are There Women Who Should Not Take Indomethacin?

Women who are more than 32 weeks pregnant should avoid indomethacin, given the potential for heart problems in the baby. Women with a history of ulcers, kidney, liver, or bleeding problems should also avoid indomethacin.