- Prevent Preterm Birth

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Prevention & Treatment


Every pregnant woman is at risk for preterm birth, but most women think it will never happen to them. When they face an episode of preterm labor, they may not know what their options are.

Between 30 and 50 percent of women who experience preterm labor will go on to deliver their babies at term, according to Edmund F. Funai, MD. Your chances of delivering your baby safely at term will be highest if you and your healthcare provider actively manage your risk of preterm birth. Whether you are currently pregnant or you are planning a pregnancy after a preemie, you'll want to discuss the options below with your doctor or midwife.



Multiple studies have shown that cervical length at approximately 20 to 24 weeks into a pregnancy is the strongest indicator of a pregnant woman's risk of preterm birth. The length of the cervix is most accurately measured by transvaginal ultrasound, which your doctor may not consider doing unless you specifically request it. Normal cervical length is 4 to 5 cm when not pregnant.

One study found that at 24 weeks gestation, the average cervical length is 3.5 cm. When cervical length is less than 2.2 cm, women face a 20 percent probability of preterm delivery. (Source: The Length of the Cervix and the Risk of Spontaneous Premature Delivery. New England Journal of Medicine; February 29, 1996; Vol. 334, Number 9: 567-572.)

Another study found that when the cervical length measures 1.5 cm or less, the risk of spontaneous preterm birth is almost 50 percent. (Source: American Journal of Obstetrics and Gynecology; June 2000; Volume 182, Issue 6, pages1458-1467)

The length of the cervix is expected to shorten as a pregnancy progresses, but a length of 3.0 cm to 3.5 cm isn't expected until 32 to 36 weeks:
  • At 16 to 20 weeks, normal cervical length is 4.0 to 4.5 cm
  • At 24 to 28 weeks, normal cervical length is 3.5 to 4.0 cm
  • At 32 to 36 weeks, normal cervical length is 3.0 to 3.5 cm


Most doctors will schedule women for a transabdominal ultrasound around 20 weeks. Ask the sonographer to take note of your cervical length at that time, and write it down for yourself as well. If the length is below 4 cm, ask the sonographer to do a transvaginal ultrasound to get a more accurate measurement. It is standard to take the measurement three times over the course of several minutes. If the length is below 4 cm and you experience ANY signs of preterm labor in the weeks that follow, request a transvaginal ultrasound so a current measurement can be compared to the previous measurement.

A short cervical length between 20 weeks and 24 weeks is the best predictor of preterm birth:
  • Length less than 1 cm: Mean birth gestational age 32 weeks
  • Length less than 1.5 cm: Mean birth gestational age 33 weeks
  • Length less than 2 cm: Mean birth gestational age 34 weeks
  • Length less than 2.5 cm: Mean birth gestational age 36.5 weeks

Source: American Journal of Obstetrics & Gynecology, June 2000

Schematic drawing of female reproductive organs, frontal view.

Source: U.S. Centers for Disease Control and Prevention

Imaging by transvaginal ultrasound can see both the top and bottom of the cervix. Your healthcare provider may describe the shortening of the top portion of the cervix as funneling, because the cervix looks like you guessed it a funnel. (Click here for an image.)

The widest part of the funnel is closest to your uterus and the most narrow part toward to vagina. When the cervix shortens even more, it will look like a “V” on ultrasound, and then a “U.” Normally the cervix is shaped like a tube. Greater than 50 percent funneling before 25 weeks is associated with 80% risk of preterm delivery, according to 

Following a transvaginal ultrasound, your doctor may want to do a manual exam to see if the cervix has softened, thinned, or dilated, which can be signs of labor being eminent or in progress.

An Ultrasound Alternative
Ultrasounds can be expensive and the equipment is not always readily available in your doctor's or midwife's office, but there is an alternative. Rosalyn Baxter-Jones, MD invented a quick and inexpensive option for a preliminary assessment of cervical length. The device is called CerviLenz and it can be described most simply as a disposable plastic ruler for measuring the length of the cervix.

The idea behind the device is that your doctor, midwife or triage nurse can take an initial measurement of the cervix, and then follow up with a transvaginal ultrasound if the CerviLenz measurement is less than 3 cm.

Multiple studies have shown the effectiveness of CerviLenz as a screening tool, including one published in the Journal of Maternal-Fetal and Neonatal Medicine (March 2013) that stated, “CerviLenz is as effective as TVU in assessing cervical length, measurements are well tolerated, and likely more readily performed by generalists.” You can learn more about the other studies here. Again, CerviLenz is a first-line diagnostic tool that is not meant to replace a transvaginal ultrasound in instances where the cervix measures less than 3 cm.


Superior outcomes have been reported in women treated with weekly intramuscular injections of 17 alpha-hydroxyprogesterone caproate (also called 17P, 17-OHP or simply "progesterone").  The American College of Obstetricians and Gynecologists has promoted the use of progesterone injections since 2003, following two randomized placebo-controlled trials. In both studies, the participants were women who had experienced a previous singleton preterm birth. In the larger study, women received the progesterone injections starting sometime between weeks 16 and 21, and continuing until delivery or week 37, whichever came first.

Women in the progesterone injections group had 34 percent fewer premature births than women given the placebo, and there was a reduction of 42 percent in the rate of preterm births before 32 weeks. In the smaller study, women who received vaginal progesterone suppositories had a preterm birth rate of 2.7 percent, compared to 18.6 percent in the placebo group.

If you have experienced a preterm birth in a previous pregnancy or if you have a short cervix in your current pregnancy, ask your doctor to explain the benefits of progesterone and how to get a prescription filled.

Makena is the brand name of the FDA-approved progesterone injection for the prevention of preterm birth, but it isn’t available at your corner pharmacy. Your healthcare provider will fill out a prescription form at and then a representative of Makena will call you with information about your insurance coverage and out-of-pocket costs. Then, a specialty pharmacy will ship the product to you. Your insurance may cover a weekly visit from a nurse to administer your injection, or a family member or healthcare professional can give it to you.

Some doctors may determine that a progesterone injection created by a compounding pharmacy may be a preferred option if, for example, you are allergic to any of the inactive ingredients of Makena, which are castor oil USP, benzyl benzoate USP and benzyl alcohol. You can find a compounding pharmacy through the International Academy of Compounding Pharmacists by calling 1-800-927-4227 or going to its website. You can send your prescription to a compounding pharmacy and it will be filled by mail.

The primary side effect of the shot is pain at the injection site, which can be compared to a mosquito bite. It will vary in pain, itchiness, and lumpiness from woman to woman and even from shot to shot.

Some insurance plans will not cover progesterone injections, but instead will cover the cost of progesterone suppositories, progesterone tablets or progesterone gel. These types of progesterone are used off-label in the prevention of preterm birth. This means these different forms of progesterone have been used in the past and have been proven safe, but the FDA will not allow the manufacturers to advertise them as effective in preventing preterm birth.

A meta-analysis of five separate studies showed that the use of a vaginal progesterone gel in women with a short cervix but no preterm labor symptoms reduced the risk of preterm birth prior to 33 weeks by 42 percent, compared to a placebo, according to an article published in the December 2011 American Journal of Obstetrics and Gynecology. There was also a significant reduction in the rate of preterm births before 35, 34, 30 and 28 weeks. Ask your doctor which option is best for you.


A cerclage is a stitch placed around the cervix to prevent it from dilating too soon. There are abdominal and vaginal cerclages. Two types of vaginal cerclages are McDonald and Shirodkar. Both of these can be performed using various different sutures (stitches). Abdominal cerclages have been performed during and prior to pregnancy and generally are done after failed vaginal procedures.

Cervical incompetence is typically characterized by painless cervical dilation leading to pregnancy loss or early preterm birth.  In most cases, it is detected when a woman comes in for a routine office visit or ultrasound and the cervix is found to be incidentally dilated on examination.  What starts out as painless dilation may turn into preterm labor once the cervix becomes very dilated.

For women diagnosed with cervical incompetence for the first time, the doctor may try to put in a cerclage if the woman is in the second trimester. This procedure can be technically challenging if the cervix is significantly dilated.  For women with a history of cervical incompetence in a prior pregnancy, treatment might involve placement of a cerclage at the end of the first trimester.


Your doctor may recommend reducing your level of activity if you begin having contractions before 37 weeks. Some contractions, called Braxton Hicks or "practice contractions," are acceptable before then, but don't hesitate to call your doctor to describe what you are feeling. Some women have what can be described as an irritable uterus. For these women, contractions can be caused by any number of activities, including bending over, climbing up and down stairs, and intercourse. Take note of how often you feel your belly tighten, and what activities cause it to tighten, and discuss this with your doctor.

Limiting your activity can also help ease the feeling of vaginal pressure you get when the baby is sitting low against your cervix. Any time you have an increase in pressure, be sure to contact your healthcare provider, especially if you're having any of these premature labor symptoms as well.

Also, ask about your cervix length. A short cervix may be causing those feelings of pressure, and a diagnosis of having a short cervix can help to identify your risk of preterm birth.


Being dehydrated can cause your uterus to start contracting. Be sure to drink at least eight 8-ounce glasses of water or other caffeine-free beverages each day. Drink even more when the weather is warm, even if you are indoors. You should be drinking enough that it makes your urine clear. A full bladder can also cause contractions, so don't wait to get to the bathroom when you feel the urge. If you are treated at the hospital for preterm labor, one of the first things they will do is start IV fluids. This is because when you are dehydrated, your blood volume decreases. As blood volume decreases, the concentration of the hormone that causes contractions (oxytocin) increases. IV fluids can't "cure" preterm labor resulting from other causes, but being well hydrated can improve blood flow to the uterus and keep amniotic fluid levels stable.


Preeclampsia accounts for 15% of preterm births in the United States. The use of low-dose aspirin has been show in clinical trials to reduce the risk of preeclampsia by 24% and the risk of preterm birth by 14%, according to an article published by the U.S. Preventive Services Task Force. The USPTF recommends that women at high risk for preeclampsia take one low-dose aspirin (81 mg) per day as a preventive medication after 12 weeks of gestation.

Risk factors for preeclampsia include a history of preeclampsia, intrauterine growth restriction (IUGR), preterm birth, placental abruption or fetal death. Risk factors that are not related to pregnancy include type 1 or 2 pre-gestational diabetes, chronic hypertension, renal disease and autoimmune diseases. The risk of preeclampsia is also higher in pregnancies with more than one baby.


If you are admitted to the hospital because of preterm labor and have not yet reached 34 weeks, your doctor may prescribe one or more of the following treatments:


Bacterial infections are a major cause of preterm labor, according to the New England Journal of Medicine. An infection in the uterus can cause the uterus to contract, which in turn may cause the amniotic sac to break early. This is called "premature rupture of membranes" or PROM . In cases of PROM that are not caused by infection, there is a high risk of subsequent infection for both mom and baby. If you suspect that your amniotic sac has broken commonly known as "your water breaking" call you doctor immediately so that specific antibiotics can be given intravenously as early as possible.

Common causes of infection that result in preterm labor include bacterial vaginosis, urinary tract infection, group B streptococcus infection, and sexually transmitted diseases.


Nearly one million pregnant women are put on bed rest each year, according to Dr. Glade B. Curtis, author of Your Pregnancy Week By Week. A few of the most common reasons for bed rest are listed below.

Incompetent cervix, an abnormally shaped or bicornuate uterus, or a short cervix: As the baby, or babies, gain weight and begin to put pressure on the cervix, the cervix may begin to open before the due date.

Episode of preterm labor or preterm birth in prior pregnancy, episode of preterm labor in current pregnancy, or irritable uterus: The goal for these three groups of high-risk women is to prevent contractions. In women with irritable uterus, contractions can be caused by nearly any movement walking up or down stairs, bending over, reaching for something, intercourse, etc.  Learn more about irritable uterus here.

High blood pressure, pregnancy induced hypertension, preeclampsia: Limited activity helps to lower the mother's blood pressure, and lying on one side or the other helps improve blood flow to the baby which can improve growth.

Placenta previa, placental abruption: In placenta previa, the placenta blocks part or all of the cervix. In the case of placental abruption, the placenta becomes detached from the uterus. Bed rest helps to reduce the bleeding that is common with these two conditions.

Premature rupture of membranes (PROM): A premature rupture of membranes causes amniotic fluid to be lost prior to labor beginning. Bed rest can keep the remaining amniotic fluid in place.

Multiple gestation being pregnant with twins, triplets, or more: Each of the conditions above is more common in a multiple gestation. Bed rest may be prescribed beginning between 20 and 24 weeks as a preventive measure.

There are potential negative side effects to bed rest, including loss of muscle tone, joint pain, blood clots, and mood changes, such as anxiety and depression. Talk to your doctor about how to avoid these side effects. There are countless women who will say bed rest kept their babies safe in the womb. And in cases where bed rest doesn't prevent a preterm birth, a mother can be confident in knowing she did all she could.


In cases of preterm labor where the birth is suspected to take place within one to seven days, two corticosteroid injections such as betamethasone or dexamethasone are given to the mother 24 hours apart. These drugs help the baby’s lungs to develop a compound called surfactant, which helps keep the lungs inflated so that babies can breathe on their own after birth. Corticosteroids have also been proven to reduce the risk of bleeding in the brain, intestinal infection, and death.

Fetuses typically begin to produce surfactant on their own around 33 to 34 weeks, so the benefits of corticosteroid injections are not as significant after 34 weeks. Prior to 24 weeks, a baby's chance of survival is slim (click here for current survival rates), so this type of treatment is unlikely to improve the outcome.

Timing the injections is important. If more than seven days pass between the injections and delivery, the effectiveness is decreased. You may wonder why you can't just get multiple rounds of injections during your pregnancy. In 2000, the National Institutes of Health reaffirmed its 1994 decision not to endorse repeated cycles of corticosteroids due to potential side effects that can include a lower birth weight and decreased brain development.

Medical opinions began to shift when a 2009 study showed that premature babies born before 34 weeks have a 31 percent reduction in serious complications when the mother is given a second round of antenatal corticosteroids. No adverse side effects were noted.

The American College of Obstetrics and Gynecology had previously followed the NIH guidelines, but officially modified its opinion in 2011 and again in 2012. ACOG said that a second round of injections (called a "rescue course") can be considered if the prior treatment was more than 7 days prior, the gestational age is less than 34 weeks, and the woman is likely to give birth within the following seven days.

Discuss your options with your doctor so that you can choose the best time to receive the injections, based on your individual circumstances.


Fetal fibronectin is a sticky protein that keeps the baby's fetal membranes attached to the mother's uterus during pregnancy. This protein is normally detected in vaginal secretions before 22 weeks and after 35 weeks when it begins to break down naturally. This test may show that fetal fibronectin is present, even before other signs of preterm labor occur. A negative result reassures you that there is more than a 99 percent chance you will not deliver within the next two weeks. A positive result does not guarantee that labor will occur within a specific time frame, but it does allow you and your doctor to treat the preterm labor more aggressively in order to prevent preterm birth.


Tocolytic medications are used to stop preterm labor. Each of these medications works in a different way and can have various side effects for mom and baby. Ask your doctor about the pros and cons of each option.

Magnesium Sulfate

Magnesium sulfate is used to slow contractions for 24 to 48 hours to allow time to administer corticosteroid injections and move the mother to a hospital with a neonatal intensive care unit NICU, if necessary. Doctors do not know exactly how magnesium sulfate works, but there are two accepted theories. One is that magnesium sulfate slows contractions of the uterus by depressing the central nervous system. The other theory is that magnesium lowers the amount of calcium in the muscle cells of the uterus, which is needed for the uterine muscles to contract. In the United States, using magnesium sulfate as a preterm labor tocolytic began in 1969. It is a popular and effective choice, but it is now being used less often because of the potential side effects for the mother and fetus, and because of the success of other tocolytic medications that result in fewer negative side effects.

In May 2013, the FDA issued a statement advising health care professionals against using magnesium sulfate injections for more than 5 to 7 days to stop preterm labor. Continuous administration of magnesium sulfate beyond that time frame can cause low calcium levels and bone changes in the developing baby.


Brand names: Procardia, Adalat
Nifedipine is a calcium-channel blocker that is used to slow or stop contractions of the uterus. This is an off-label use of this antihypertensive medication, which is traditionally used to treat high blood pressure and heart disease. It works by blocking the calcium that is needed for the smooth muscle tissue of the uterus to contract. If labor is successfully stopped, a doctor may prescribe nifedipine for at-home use until the pregnancy reaches a less-risky stage such as 34 weeks, or up to 37 weeks . According to the American Journal of Perinatalogy, altered urinary calcium excretion may be less reflective of the progression in severity of preeclampsia in patients treated with nifedipine. Also, in a May 2005 article in OBG Management, Dr. Baha M. Sibai of the University of Cincinnati College of Medicine wrote that antihypertensive drugs may mask preeclampsia. If you are on nifedipine for more than a few days, be sure your doctor is closely monitoring your risk of preeclampsia, for which the symptoms may include any of the following: hyperactive reflexes; swelling in the hands, feet, and/or face; protein in the urine; blood pressure above 140 over 90, either during the time nifedipine is being taken or in the weeks that follow.


Brand name: Indocin
Indomethacin is a nonsteroidal anti-inflammatory drug NSAID . It prevents the production of prostaglandins, which cause contractions. Indomethacin is used to slow contractions for 24 to 48 hours to allow time to administer corticosteroid injections and move the mother to a hospital with a neonatal intensive care unit NICU, if necessary. Indomethacin can be used when beta-sympathetic medications such as terbutaline and ritodrine fail to stop contractions, or when there may be an increased risk of side effects from beta-sympathetics due to heart disease, lung disease or diabetes.


Brand names: Brethine, Bricanyl
Terbutaline is used to treat asthma and other breathing conditions, but it is also commonly used "off-label" to treat preterm labor. Terbutaline relaxes the smooth muscles of the uterus to slow contractions. On February 17, 2011, the FDA released a safety announcement that clinicians should not use injectable terbutaline to prevent preterm labor or treat it beyond 48 to 72 hours because of the risk for maternal heart problems and death.  Also, oral terbutaline should not be used for the prevention or any treatment of preterm labor because it shares the same safety risks as the injectable version and has not proven to be effective. The FDA has determined that the cardiovascular risks outweigh any potential benefit to pregnant women receiving terbutaline by injection or by infusion pump on a prolonged basis, or any treatment with the oral tablet version of the drug.

 "Although it may be clinically deemed appropriate based on the health care professional's judgment to administer terbutaline by injection in urgent and individual obstetrical situations in a hospital setting, the prolonged use of this drug to prevent recurrent preterm labor can result in maternal heart problems and death," the statement said. Terbutaline should not be used in the outpatient or home setting. The FDA statement acknowledges that there are serious situations where a healthcare professional may decide that the short-term use of injectable terbutaline may benefit a pregnant woman, but stated that such treatment should not extend beyond 48 to 72 hours. This amount of time allows the administration of corticosteroid injections for fetal lung development and to move the mother to a hospital with a neonatal intensive care unit, if necessary.

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Warning Sign #1

Warning Sign


If you are less than 37 weeks along, call your doctor immediately if you have more than four contractions in one hour, or cramping that feels like menstrual pain.

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