Preterm Labor

Topic Overview

Is this topic for you?

This topic covers preterm labor as it relates to the pregnant woman's problems and care. If you are looking for information about babies who are born too soon, see the topic Premature Infant. Labor and delivery before the end of 20 weeks of pregnancy is called a miscarriage. See the topic Miscarriage for more information.

What is preterm labor?

Preterm labor is the start of labor between 20 and 37 weeks of pregnancy. A full-term pregnancy lasts 37 to 42 weeks. In labor, the uterus contracts to open the cervix. This is the first stage of childbirth.

Preterm labor is also called premature labor.

What are the risks of preterm labor and preterm birth?

The earlier the delivery, the greater the risk for serious problems for the baby. This is because many of the organs—especially the heart and lungs—are not fully grown, or mature. Premature infants born after 32 weeks of pregnancy tend to have less chance of problems than those born earlier.

For infants born before 24 weeks of pregnancy, the chances of survival are extremely slim. Many who do survive have long-term health problems. They may also have other problems, such as trouble with learning and talking and with moving their body (poor motor skills).

What causes preterm labor?

Preterm labor can be caused by a problem with the baby, the mother, or both. Often the cause is not known.

Preterm labor most often occurs naturally. But sometimes a doctor uses medicine or other methods to start labor early because of pregnancy problems that are dangerous to the mother or her baby.

Causes of preterm labor include:

  • The placenta separating early from the uterus. This is called placenta abruptio.
  • Elevated blood pressure or pre-eclampsia.
  • Being pregnant with more than one baby, such as twins or triplets.
  • An infection in the mother’s uterus that leads to the start of labor.
  • Problems with the uterus or cervix.
  • Drug or alcohol use during pregnancy.
  • The mother’s water (amniotic fluid) breaking before contractions start.

Treatments to help a woman get pregnant have led to more women being pregnant with more than one baby, such as twins or triplets. This has also increased the number of women who have preterm labor and preterm births.

What are the symptoms?

It can be hard to tell when labor starts, especially when it starts early. So watch for these symptoms:

  • Regular contractions for an hour. This means about 4 or more in 20 minutes, or about 8 or more within 1 hour, even after you have had a glass of water and are resting.
  • Leaking or gushing of fluid from your vagina. You may notice that it is pink or reddish.
  • Pain that feels like menstrual cramps, with or without diarrhea.
  • A feeling of pressure in your pelvis or lower belly.
  • A dull ache in your lower back, pelvic area, lower belly, or thighs that does not go away.
  • Not feeling well, including having a fever you can't explain and being overly tired. Your belly may hurt when you press on it.

If your contractions stop, they may have been Braxton Hicks contractions. These are a sometimes uncomfortable, but not painful, tightening of the uterus. They are like practice contractions. But sometimes it can be hard to tell the difference.

If preterm labor contractions do not stop, the cervix begins to open (dilate) or thin (efface). Before or after contractions begin, the amniotic sac that holds the baby may break. This is called a rupture of membranes. It causes a leakage or a gush of amniotic fluid. Rupture of membranes before contractions start is called premature rupture of membranes, or PROM. Before 37 weeks of pregnancy, it is called preterm premature rupture of membranes, or pPROM.

How is preterm labor diagnosed?

If you think you have symptoms of preterm labor, call your doctor or certified nurse-midwife. He or she can check to see if your water has broken, if you have an infection, or if your cervix is starting to dilate. You may also have urine and blood tests to check for problems that can cause preterm labor. Checking the baby’s heartbeat and doing an ultrasound can give your doctor or midwife a good picture of how your baby is doing. Amniotic fluid can be tested for signs that your baby’s lungs have grown enough for delivery.

You may have a painless swab test for a protein in the vagina called fetal fibronectin. If the test does not find the protein, then you are unlikely to deliver soon. But the test cannot tell for certain if you are about to have a preterm birth.

How is it treated?

If you are in preterm labor, your doctor or certified nurse-midwife must weigh the risks of early delivery against the risks of waiting to deliver. Depending on your situation, your doctor or midwife may:

  • Try to delay the birth with medicine. This may or may not work.
  • Use antibiotics to treat or prevent infection. If your amniotic sac has broken early, you have a high risk of infection and must be watched closely.
  • Give you steroid medicine to help prepare your baby’s lungs for birth. This treatment has some risks, but it can improve your baby’s chances of surviving a premature birth between 24 and 34 weeks of pregnancy.1
  • Treat any other medical problems causing trouble in pregnancy.
  • Allow the labor to go on because delivery is safer for the mother and baby than letting the pregnancy go on.

Frequently Asked Questions

Learning about preterm labor:

Being diagnosed:

Getting treatment:

Ongoing concerns:

Cause

Preterm labor can be caused by a problem involving the fetus, the mother, or both. Often a combination of several factors is responsible. But in about 1 out of 3 preterm births, the cause is not known.2

Causes of spontaneous preterm labor include:

Symptoms

Preterm labor often starts without obvious symptoms. But you may notice one or more symptoms, including:

  • Menstrual-like cramps, with or without diarrhea.
  • A feeling of pressure in your pelvis or lower abdomen.
  • A persistent, dull ache in your lower back, pelvic area, lower abdomen, or thighs.
  • Changes in your vaginal discharge, which may increase in amount or become pink or reddish.
  • Regular contractions of your uterus for an hour. This means about 4 or more in 20 minutes, or about 8 or more within 1 hour, even after you have had a glass of water and are resting.
  • Not feeling well, including:
    • Unexplained fever.
    • Fatigue.
    • Uterine tenderness.

It is sometimes hard to tell the difference between Braxton Hicks contractions and preterm labor contractions.

You may have one or more of these symptoms and not be in preterm labor. But if you are concerned, notify your doctor or nurse-midwife.

What Happens

If preterm labor occurs close to your due date (in the 35th or 36th week of pregnancy), you may be allowed to deliver without delay. Preterm birth at this point in a pregnancy usually results in few or no serious complications.

Symptoms of preterm labor do not necessarily mean that preterm birth will happen. Your doctor may be able to stop your preterm labor.

If preterm labor contractions do not stop, the cervix may thin (efface) and open (dilate). The amniotic sac may break (rupture), leading to preterm birth.

The method of delivery used in premature labor depends on the health of the mother and fetus. In most cases a woman can deliver vaginally. If the health of the mother or fetus is at risk, a cesarean section may be needed. See the topic Pregnancy for more information.

Sometimes a pregnancy poses a great enough health risk to a mother or her fetus that it is necessary to deliver by cesarean or induce labor for a preterm vaginal delivery. This is called an indicated preterm birth, accounting for about 25% of preterm births.3

Premature infant

The more prematurely an infant is born, the greater the risk of medical complications of prematurity. A premature fetus's likelihood of survival increases as the pregnancy advances and as the fetus gains weight. The fetus's stage of development, ability to breathe (lung maturity), and overall health are also important factors for survival. Because of advances in medical care, more premature infants are surviving today than in years past. For more information, see the topic Premature Infant.

What Increases Your Risk

It is hard to predict who is at risk for preterm labor. Some women with risk factors do not have early labor. Others with no known risk factors do have early labor.

Preterm labor and preterm birth

Most premature births happen after naturally occurring, or spontaneous, preterm labor (as opposed to a medically necessary preterm birth, when the baby must be delivered as quickly as possible to prevent harm to mother or baby).

Experts say that spontaneous preterm labor is often the result of a combination of factors. Some of the most common medical risk factors for a spontaneous preterm birth are:

  • Pregnancy with twins, triplets, or more. (Use of assisted reproductive technology (ART) or superovulation increases the risk of multiple pregnancy, which carries a high risk of premature birth and resulting medical complications.4)
  • In vitro fertilization (IVF) , a type of ART. IVF twins may be born earlier than naturally-conceived twins.4
  • A past preterm delivery.
  • Vaginal bleeding in the second trimester.
  • Infection in the urinary or reproductive tract, including the vagina.
  • Age younger than 18 years.
  • Mother's low body weight for height (body mass index).
  • Cigarette smoking during pregnancy.
  • Frequent contractions.

Other factors that may increase your risk for premature labor include:

When To Call a Doctor

Preterm labor can be difficult to recognize. Get the earliest possible medical care for preterm labor by calling your doctor or your nurse-midwife about signs of possible preterm labor.

Any time during your pregnancy

Call your doctor or your nurse-midwife if you have:

  • An increase or gush of fluid from your vagina. It is possible to mistake a leak of amniotic fluid for a problem with bladder control or excess cervical mucus.
  • Bleeding or spotting from your vagina.
  • Painful or frequent urination or urine that is cloudy, foul-smelling, or bloody.

Between 20 and 37 weeks of your pregnancy

Call your doctor, your nurse-midwife, or the labor and delivery unit of your local hospital if:

  • You have had regular contractions for an hour. This means about 4 or more in 20 minutes, or about 8 or more within 1 hour, even after you have had a glass of water and are resting.
  • You have unexplained low back pain or pelvic pressure.
  • You have uterine tenderness, unexplained fever, or weakness (possible symptoms of infection).
  • You have intestinal cramping with or without diarrhea.
  • The baby has stopped moving or is moving much less than normal. See fetal movement counting for information on how to check your baby's activity.

Watchful Waiting

If you are having painless or mild contractions that are irregular or more than 15 minutes apart:

  • Stop what you are doing.
  • Empty your bladder.
  • Drink 2 to 3 glasses of water or juice (too little body fluid can cause contractions).
  • Lie down on your left side for at least an hour, and keep track of how often you have contractions.

Call your doctor if you have had regular contractions for an hour. This means about 4 or more in 20 minutes, or about 8 or more within 1 hour, even after you have had a glass of water and are resting.

If your contractions stop, they were probably Braxton Hicks contractions, which are harmless and normal. Braxton Hicks contractions are often irregularly timed and uncomfortable rather than painful.

Who To See

If you are in premature labor, you may be seen by:

You may continue to see your certified nurse-midwife or certified professional midwife, who will consult with one of the doctors listed above.

If it appears that your labor cannot be stopped, you may also see a neonatologist, a doctor who specializes in the intensive care of infants.

To prepare for your appointment, see the topic Making the Most of Your Appointment.

Exams and Tests

If you have symptoms of preterm labor, both you and your fetus will be examined and monitored.

For the mother

You will be examined for tenderness in your uterus. Your temperature, pulse, and rate of breathing will be checked. Depending on the nature of your symptoms, you may have one or more exams or tests, including:

  • A vaginal exam, to find out whether the contractions have begun to open (dilate) or thin (efface) your cervix.
  • A vaginal smear, which may be collected to check for:
    • Infection, with a vaginal culture. Disease-causing organisms in the vagina can cause uterine infection, triggering preterm labor and serious infection in the newborn.
    • Amniotic fluid, which shows that the amniotic sac has broken.
    • Fetal fibronectin, which does not tell for sure if you are having preterm labor. When the test is negative, it is unlikely that you are having preterm labor. But even if the test is positive, it does not mean for sure that you are having preterm labor.3 This test is not useful for actually predicting preterm labor and is not used in all labor and delivery units. It is done before a pelvic exam to reduce the risk of a false-positive result.

Other tests that may be done to check for infection include:

If an infection is present, you may be treated with antibiotics.

For the fetus

  • Your fetus's health is checked using electronic fetal heart monitoring, which records fetal heartbeats. Fetal monitoring also checks, records, and times the mother's contractions and shows how the fetus's heart rate reacts to each uterine contraction.
  • A fetal ultrasound test may be used to:
    • Find out whether more than one fetus is in the uterus.
    • Estimate the age, weight, and position of the fetus.
    • Locate and check the condition of the placenta.
    • Check the length of the cervix. A short cervix is a sign that preterm labor may be likely to happen.
  • Amniocentesis is sometimes used to take amniotic fluid from the uterus. This test is most commonly used to test the amniotic fluid for:
    • Signs of infection.
    • Substances that show whether the fetus can breathe without assistance, in case of premature birth.

All of this information can help you and your doctor or nurse-midwife decide whether to treat premature labor and delay the birth or allow premature labor to continue and manage any complications that might occur.

Treatment Overview

Treatment to slow your preterm labor contractions may be used if:

  • You are between 23 and 34 completed weeks of pregnancy.
  • You are having regular contractions. This means about 4 or more in 20 minutes, or about 8 or more within 1 hour, even after you have had a glass of water and are resting.
  • Your cervix has opened (dilated) to more than 2 centimeters and has begun to thin (efface).

Preterm labor is not always treated. When a pregnancy is nearing term (about 37 or more weeks), or when the mother or her fetus has a serious medical problem, preterm labor is usually allowed to continue until delivery.

When deciding on the amount and type of treatment, your doctor or nurse-midwife will think about:

If you are treated for preterm labor

Preterm labor is usually treated in the hospital, in the labor and delivery area. Whether your amniotic membranes have ruptured before contractions start (preterm premature rupture of membranes, or pPROM) or after contractions have begun (spontaneous rupture of membranes, or SROM), you will be admitted directly to the labor and delivery unit. If rupture of membranes has not occurred, you will be observed for at least an hour or two to see whether your contractions continue and your cervix changes (opens and thins).

  • If your cervix does not change, or if your contractions stop or slow down, you may be sent home.
  • If your cervix changes, you will be admitted to the labor and delivery unit.

If you are admitted to the labor and delivery unit, your doctor or nurse-midwife may choose to:

  • Use medicine to try to slow or stop the contractions, thus preventing the cervix from opening wider (dilating) or becoming thinner (effacing). Short-term treatment with tocolytic medicine is the current treatment. If effective, tocolytics may delay birth for more than 48 hours.6
  • Treat or prevent infection with antibiotics.
  • Help the fetus's lungs mature quickly with antenatal corticosteroids (given to you). These medicines take 24 to 48 hours to benefit the fetus.

There is no evidence that long-term bed rest lowers the risk of preterm delivery.7 But your doctor may advise you to take it easy and try to rest as much as possible. Studies have shown that strict bed rest for 3 days or more may increase your risk of getting a blood clot in the legs or lungs.8 Strict bed rest is no longer used to prevent preterm labor. But if your doctor has recommended expectant management with some bed rest (partial bed rest), remember to flex your feet, stretch, and move your legs as much as possible.

Cervical cerclage is the placement of stitches in the cervix to hold it closed. It is rarely done. Cerclage is meant to stop the cervix from opening early, which could lead to miscarriage or preterm birth. It has helped some high-risk pregnancies last longer, but cerclage also has risks. It can cause infection or miscarriage. For a woman who has had a preterm birth in the past because her cervix did not stay closed, cervical cerclage may prevent another preterm birth.2

What To Think About

Dehydration is a common cause of temporary preterm contractions. At the first sign of possible contractions, be sure to drink extra fluids. If dehydration is the cause, your contractions should subside.

Tocolytic medicines can be effective for delaying delivery for 1 to 2 days so that other medicine (antenatal corticosteroids) can be given to help the fetus's lungs mature. But there is no evidence that tocolytic medicines prolong pregnancy or improve infant survival when given for longer periods of time.7 They can also have serious side effects on the mother, the fetus, or both. For more information, see the Medications section of this topic.

For information about having a premature infant, see the topic Premature Infant.

Prevention

Even if you have a healthy pregnancy, you may go into preterm labor. It is difficult to prevent preterm labor because it is usually not anticipated. Also, it is often due to causes that are not completely understood. But following some general guidelines for a healthy pregnancy may help prevent preterm labor and will optimize your fetus's health and ability to thrive, whether at full term or preterm.

Being pregnant with twins, triplets, or more puts you at high risk for preterm labor and infant complications. If you are planning to use assisted reproductive technology or superovulation to conceive, talk to your doctor about reducing your risk of conceiving more than one baby. For more information, see the topics Fertility Problems and Multiple Pregnancy: Twins or More.

If contractions start

Contractions are a normal part of all pregnancies. Most contractions do not thin and open the cervix. Rather, they are simply a brief stimulation of the uterine muscle. This can happen when your fetus is moving a lot, when your bladder or bowel is full, or when you are dehydrated. These non-labor contractions are irregularly timed and uncomfortable rather than painful.

Preterm labor contractions tend to be regularly timed, becoming more frequent, painful, and prolonged (30 to 60 seconds) as they progress. You may also notice low back pain, thigh pain, or increased vaginal discharge or bleeding.

If you are less than 37 weeks pregnant and your uterus is contracting more than usual (about 4 or more in 20 minutes or about 8 or more within 1 hour), the following steps may stop your contractions:

  • Drink 2 or 3 glasses of water or juice (not having enough liquids can cause contractions).
  • Stop what you are doing, empty your bladder, and lie down on your left side for at least an hour.

If your symptoms get worse during the hour, call your doctor or nurse-midwife or go to the hospital.

If you are at risk for preterm labor

If you have had a spontaneous preterm birth before, you are probably at high risk for another preterm labor. This might make you a candidate for weekly progesterone injections for preventing preterm labor and delivery. This is a promising new approach, though it isn't yet widely used in all areas of the country. No fetal or newborn harm has been observed, though ongoing research is needed to rule out long-term side effects.9

You may be able to help prevent preterm labor if you are at risk (see the What Increases Your Risk section of this topic). Avoid activities that can start contractions.

  • Avoid using drugs such as cocaine and methamphetamines.
  • Don't smoke.
  • Eat a healthy diet that is low in saturated fat. Use olive or canola oil in place of other fats or oils. Get lots of whole grains, low-fat dairy, fruits, and vegetables.

Home Treatment

Symptoms of preterm labor are warning signs. They do not necessarily mean that you will have a preterm birth.

At home, you can avoid activities that can start contractions.

  • Avoid using drugs such as cocaine and methamphetamine.
  • Do not smoke.

If you are less than 37 weeks pregnant and your uterus is contracting more than usual, the following steps may stop your contractions:

  • Drink 2 or 3 glasses of water or juice. Not having enough liquids can cause contractions.
  • Stop what you are doing, empty your bladder, and lie down on your left side for at least 1 hour.
  • Try to remember what you were doing when the symptoms started so that you can avoid starting the contractions again later.
  • If your contractions get worse during the hour, call your doctor or nurse-midwife, or go to the hospital.

Although stress is not considered a direct cause of preterm labor, do what you can to reduce stress in your life for your own good. Try to do less, ask for help, and eat well.

If you have already been treated for preterm labor

If your contractions stop, you may be sent home from the hospital. Before you are discharged, you should know:

  • The symptoms of preterm labor, including lower pelvic ache or backache, pressure, or cramps.
  • What to do if preterm labor starts again, including drinking fluids, resting, and calling your doctor if symptoms don't improve in 1 hour.
  • When to call your doctor or nurse-midwife. See the When to Call a Doctor section of this topic.

Medications

If your contractions are causing changes in your cervix (preterm labor), or you have signs of infection or preterm premature rupture of membranes (pPROM), you may be treated with one or more medicines, including:

  • Antibiotics, to prevent or treat infection. Antibiotic treatment does not always get rid of infection. But it often prevents infection when the amniotic sac has ruptured (pPROM) and can also delay delivery after pPROM.2
  • Medicines (antenatal corticosteroids) to speed up fetal lung development if birth is anticipated between the 24th and 34th weeks of pregnancy.
  • Tocolytic medicines, to slow down contractions and try to delay labor for a day or two.

Delaying labor even for a short time can allow you to be:

  • Transported to a medical center that has a neonatal intensive care unit (NICU).
  • Given antenatal corticosteroids, which take a minimum of 48 hours to fully benefit a fetus's lungs. Even 24 hours provides some benefit.

Medication Choices

Antibiotic medicine is chosen by your doctor or nurse-midwife based on the type of infection present.

Antenatal corticosteroids (betamethasone or dexamethasone) help prepare the fetus's lungs for preterm birth.

Tocolytic medicines that are used to stop preterm labor include:

What To Think About

If you have had a spontaneous preterm birth in the past, you are probably at high risk for another preterm labor. This might make you a possible candidate for weekly progesterone for preventing preterm labor and delivery. This is a promising new approach, though it isn't yet widely used in all areas of the country. Also, the type of progesterone used, 17 alpha-hydroxyprogesterone caproate, is not widely available. No fetal or newborn harm has been observed, though long-term research has not been done to rule out long-term side effects.9

A single course of antenatal corticosteroid treatment, used to prepare the fetus's lungs for birth, is considered to be the least risky, most effective treatment available for avoiding the most common preterm fetal complications at birth. It is standard procedure to give corticosteroid injections to most women before preterm birth, especially for pregnancies at 24 to 34 weeks of gestation.

If you test positive for infection, you will be treated with an antibiotic during pregnancy or labor in an attempt to prevent infection in your newborn. This is why women with preterm premature rupture of membranes (pPROM) are screened for group B strep (GBS).

Antibiotic treatment for preterm labor is:

  • Beneficial for women with pPROM. Antibiotics may delay labor and reduce risk of newborn infection.2
  • Used for women whose GBS diagnosis is unknown. Then if a GBS test is negative, the antibiotic may be stopped.
  • Not recommended for women with intact membranes and no evidence of infection.

Tocolytic medicines are used to delay preterm birth for a day or more so that antenatal corticosteroids can work. Tocolytics cause side effects that may require stopping treatment or trying a different tocolytic medicine. Side effects are closely monitored and rarely cause permanent damage to the mother or fetus but can be unpleasant for the mother (see information on the specific medicines). During tocolytic treatment, a woman is usually on continuous fetal monitoring and her vital signs are checked often.

Considerations before using tocolytics include your and your fetus's health, how far your labor has progressed, whether your membranes have ruptured, and whether you have an infection. Certain tocolytic medicines can be dangerous when a fetus is showing signs of distress or for women with certain health conditions (such as heart problems, severe pre-eclampsia, or poorly controlled diabetes or high blood pressure). Magnesium sulfate is being used less than it was used in the past. Studies show it does not stop preterm labor and it may cause complications for both mother and baby.10

Surgery

Surgery is rarely done to prevent preterm birth.

Cervical cerclage is the placement of stitches in the cervix to hold it closed during pregnancy. It is rarely done. It is meant to stop an incompetent cervix from opening early (which could lead to miscarriage or preterm birth).

Surgery Choices

Cervical cerclage (placement of stitches in the cervix to hold it closed, with the intention of preventing preterm labor and delivery)

What To Think About

Cerclage has helped some high-risk pregnancies last longer, but it also has risks. It can cause infection or miscarriage. For a woman who has had a preterm birth in the past because her cervix did not stay closed, cervical cerclage may prevent another preterm birth.2

Other Treatment

There are no other treatment choices for preterm labor.

References

Citations

  1. Roberts D, Dalziel S (2006). Antenatal corticosteroids for accelerating fetal lung maturation for women at risk of preterm birth. Cochrane Database of Systemic Reviews (3). Oxford: Update Software.
  2. Haas DM (2008). Preterm birth, search date June 2007. Online version of BMJ Clinical Evidence: htp://www.clinicalevidence.com.
  3. Iams JD, Creasy RK (2004). Preterm labor and delivery. In RK Creasy et al., eds., Maternal-Fetal Medicine: Principles and Practice, 5th ed., pp. 623–661. Philadelphia: Saunders.
  4. McDonald S, et al. (2005). Perinatal outcomes of in vitro fertilization twins: A systematic review and meta-analyses. American Journal of Obstetrics and Gynecology, 193: 141–152.
  5. Samson SA, et al. (2005). The effect of loop electrosurgical excision procedure on future pregnancy outcomes. Obstetrics and Gynecology, 105(2): 325–332.
  6. American Academy of Pediatrics and American College of Obstetricians and Gynecologists (2007). Obstetric and medical complications. In Guidelines for Perinatal Care, 6th ed., pp. 175–204. Elk Grove Village, IL: American Academy of Pediatrics.
  7. American College of Obstetricians and Gynecologists (2003, reaffirmed 2006). Management of preterm labor. ACOG Practice Bulletin No. 43. Obstetrics and Gynecology, 101(5): 1039–1047.
  8. Cunningham FG, et al. (2005). Preterm birth. In Williams Obstetrics, 22nd ed., pp. 855–880. New York: McGraw-Hill.
  9. American College of Obstetricians and Gynecologists (2008). Use of progesterone to reduce preterm birth. ACOG Committee Opinion No. 419. Obstetrics and Gynecology, 112: 963–965.
  10. Grimes DA, Nanda K (2006). Magnesium sulfate tocolysis: Time to quit. Obstetrics and Gynecology, 108(4): 986–989.

Other Works Consulted

  • American College of Obstetricians and Gynecologists (2007). Premature rupture of membranes. ACOG Practice Bulletin No. 80. Obstetrics and Gynecology, 109(4): 1007–1019.
  • Murphy KE, et al. (2008). Multiple courses of antenatal corticosteroids for preterm birth (MACS): A randomised controlled trial. Lancet, 372(9656): 2143–2151.
  • U.S. Preventive Services Task Force (2008). Screening for bacterial vaginosis in pregnancy to prevent preterm delivery: U.S. Preventive Services Task Force Recommendation Statement. Annals of Internal Medicine, 148(3): 214–219.
  • Yost NP, et al. (2006). Effect of coitus on recurrent preterm birth. Obstetrics and Gynecology, 107(4): 793–797.

Credits

Author Sandy Jocoy, RN
Editor Kathleen M. Ariss, MS
Associate Editor Pat Truman, MATC
Primary Medical Reviewer Sarah Marshall, MD - Family Medicine
Specialist Medical Reviewer Deborah A. Penava, BA, MD, FRCSC, MPH - Obstetrics and Gynecology
Last Updated January 14, 2009

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