Preventing Preterm Birth

Pregnant Woman And Partner Having 4D Ultrasound Scan

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.

Can You Prevent Preterm Labor And Preterm Birth?

Cervical Length And Other Cervical Changes

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.

What is a short cervix?
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

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.

Progesterone Injections, Suppositories And Gel

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.

Surgical Cerclage

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.

Restricted Activity

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.

Staying Hydrated/Intravenous Fluids

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.

Low-Dose Aspirin

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.


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