What causes preterm labor is not well understood. However, certain conditions may make it more likely:
Previous preterm deliveries
Genital infections Overview of Vaginal Infections In the United States, vaginal infections are one of the most common reasons women see their doctor, accounting for millions of visits each year. Vaginal infections are caused by microorganisms... read more , including some sexually transmitted diseases
Infections of the kidneys Kidney Infection Pyelonephritis is a bacterial infection of one or both kidneys. Infection can spread up the urinary tract to the kidneys, or uncommonly the kidneys may become infected through bacteria in the... read more or the membranes containing the fetus (intra-amniotic infection Intra-Amniotic Infection Intra-amniotic infection is infection of the tissues around the fetus, such as the fluid that surrounds the fetus (amniotic fluid), the placenta, the membranes around the fetus, or a combination... read more )
Abnormalities in the placenta, uterus, or fetus
A healthy lifestyle during pregnancy can help reduce the risk of preterm labor, as can regular visits to the doctor or midwife, who can then identify potential problems early.
Babies born prematurely Premature Newborn A premature newborn is a baby delivered before 37 weeks of gestation. Depending on when they are born, premature newborns have underdeveloped organs, which may not be ready to function outside... read more can have serious health problems, such as bleeding in the brain. When there is bleeding in the brain, the brain may not develop normally, causing problems such as cerebral palsy Cerebral Palsy (CP) Cerebral palsy refers to a group of symptoms that involve difficulty moving and muscle stiffness (spasticity). It results from brain malformations that occur before birth as the brain is developing... read more . Thus, doctors try to prevent or stop labor that begins before the 34th week of pregnancy. Preterm labor is difficult to stop.
The diagnosis of preterm labor is usually obvious, based on the signs that labor is starting and the length of the pregnancy.
Samples may be taken from the cervix, vagina, and anus to culture. Analysis of these samples may suggest a specific infection as the cause of preterm labor.
A sample of urine may be analyzed and cultured (placed in conditions that encourage the growth of microorganisms) to check for kidney and bladder infections.
If vaginal bleeding occurs or the membranes around the fetus rupture, allowing labor to continue is often best.
If vaginal bleeding does not occur and the membranes are not leaking amniotic fluid (the fluid that surrounds the fetus in the uterus), the woman is advised to rest and to limit her activities as much as possible, preferably to sedentary ones. She is given fluids and may be given drugs that can slow labor. These measures can often delay labor for a brief time.
Drugs that can slow labor include the following:
Magnesium sulfate: This drug is often given intravenously to stop preterm labor, particularly if the pregnancy is less than 32 weeks. Magnesium sulfate also appears to substantially reduce the risk of bleeding in the brain and the resulting problems with development of the newborn's brain, such as cerebral palsy. However, if the dose is too high, it may affect the woman’s heart and breathing rates.
Calcium channel blockers: These drugs are usually used to treat high blood pressure. They sometimes cause headaches and low blood pressure in the woman.
Prostaglandin inhibitors: These drugs may temporarily reduce the amount of amniotic fluid. They are not used after the 32nd week of pregnancy because they may cause heart problems in the fetus.
Women are given antibiotics until culture results are obtained. If results are negative, the antibiotics are then stopped.
If the cervix opens (dilates) more than 2 inches (5 centimeters), labor usually continues until the baby is born.
If the membranes rupture between the 24th and 34th week of pregnancy, corticosteroids are given to help the fetus’s lungs mature, unless delivery is expected soon. Doctors also consider giving women corticosteroids if the membranes rupture
The corticosteroid helps the fetus’s lungs and other organs mature more quickly. It also reduces the risk that after birth, the baby will have difficulty breathing (neonatal respiratory distress syndrome Respiratory Distress Syndrome in Newborns Respiratory distress syndrome is a lung disorder in premature newborns in which the air sacs in their lungs do not remain open because a substance that coats the air sacs called surfactant is... read more ) or other problems related to prematurity (such as bleeding in the brain).
In future pregnancies, women who have had a preterm delivery may be given a progestin. This drug may reduce the risk of having another preterm delivery. The progestin is started during the 2nd trimester and continued until just before delivery.