About 1 in 10 babies in the United States is born preterm, meaning before 37 weeks of pregnancy. The 2024 national preterm birth rate was 10.41%, with significantly higher rates among Black mothers (14.86%) and American Indian and Alaska Native mothers (12.59%). Some risk factors for preterm labor are outside your control, but several proven strategies can meaningfully lower your chances.
Cervical Length Screening
One of the strongest predictors of preterm birth is a short cervix. During the second trimester, typically between 18 and 24 weeks, your provider can measure your cervix using a transvaginal ultrasound. A cervix measuring 25 millimeters or shorter at this stage is considered short, which occurs in roughly 1% to 3% of pregnancies at 20 weeks. That single measurement can identify about a third of spontaneous preterm births that would happen before 35 weeks.
This screening window matters. After 24 weeks, the same 25-millimeter cutoff becomes far less useful, catching only about 20% of women who will deliver early. If you have a history of preterm birth or second-trimester pregnancy loss, ask about cervical length monitoring early in the second trimester. Early detection opens the door to interventions that can help keep the pregnancy going longer.
Progesterone for a Short Cervix
If screening reveals a shortened cervix and you have a history of preterm birth, vaginal progesterone is one option your provider may discuss. This hormone supplement helps maintain the cervix and reduce the chance of early delivery. ACOG’s updated guidance is specific: vaginal progesterone may be considered for women carrying a single baby who have both a prior preterm birth and a shortened cervix.
The key detail is that progesterone has not been shown to work without a short cervix. If your cervix is a normal length, progesterone supplementation is not recommended for preventing recurrent preterm birth. An older injectable form of progesterone (17-OHPC) was once widely used, but the FDA determined there wasn’t enough evidence that it was effective across the broad population it was approved for. The decision about whether progesterone is right for you depends on your cervical length, pregnancy history, and past treatments.
Cervical Cerclage
For women whose cervix begins opening too early, a procedure called cervical cerclage places a stitch around the cervix to help keep it closed. This is typically done in three situations: you have a history of second-trimester losses or very early preterm births, your cervix measures 25 millimeters or shorter on ultrasound before 24 weeks along with a relevant history, or a physical exam reveals your cervix is already dilating without contractions.
When placed based on history alone, the procedure is usually done around 14 to 16 weeks. When ultrasound findings trigger the decision, it can be placed up to 24 weeks. The stitch is removed later in the third trimester, usually around 36 to 37 weeks, before labor begins.
Managing Infections Early
Urinary tract infections during pregnancy, even ones that cause no symptoms, are linked to higher rates of preterm delivery and low birth weight. That’s why a urine culture is recommended early in prenatal care to check for bacteria. This screening catches what’s called asymptomatic bacteriuria, a bacterial presence you wouldn’t notice on your own.
Treating these silent infections reduces the risk of kidney infection during pregnancy, and at least two major studies found it also lowers preterm birth rates. If you develop symptoms like painful urination, blood in your urine, or increased frequency, a 5 to 7 day course of antibiotics is standard. After treatment, your provider may recheck your urine to confirm the infection has cleared, and if infections keep coming back, a low-dose daily antibiotic for the rest of the pregnancy may be considered.
Blood Pressure Control
High blood pressure is one of the leading reasons babies need to be delivered early for medical safety. Whether you entered pregnancy with chronic hypertension or developed it during pregnancy (gestational hypertension), keeping your blood pressure in a safe range protects both you and your baby. The general target is around 110 to 140 systolic over 80 to 90 diastolic.
Severe hypertension, defined as 160/110 or above, requires urgent hospital management. Regular blood pressure monitoring throughout pregnancy, including home monitoring in some cases, helps catch rising numbers before they become dangerous. Your provider will also watch for signs of preeclampsia, a related condition that can force an early delivery. Consistent prenatal visits are one of the simplest ways to stay ahead of blood pressure problems.
Quitting Smoking
Smoking during pregnancy is one of the most modifiable risk factors for preterm birth. Women who quit smoking, especially early in pregnancy, reduce their risk of preterm delivery by up to 20%, even among heavy smokers. The earlier you stop, the greater the benefit.
For pregnant women who smoke, behavioral approaches like counseling and structured support programs are the recommended path. The evidence on nicotine replacement therapy during pregnancy is limited and conflicting, so it’s not routinely advised. If you’re struggling to quit, your prenatal care team can connect you with cessation resources designed specifically for pregnancy.
Pregnancy Spacing
How long you wait between delivering one baby and conceiving the next has a real effect on preterm birth risk. A large study published in the New England Journal of Medicine found the lowest risk of adverse outcomes when conception happened 18 to 23 months after a previous live birth. Intervals shorter or longer than that window were both associated with higher risks.
This doesn’t mean you need to time things perfectly, but if you’ve recently delivered and are thinking about your next pregnancy, aiming for at least 18 months between delivery and your next conception gives your body time to recover nutritionally and physically.
Weight Gain During Pregnancy
Gaining too little or too much weight during pregnancy can both increase preterm risk. The recommended ranges depend on your pre-pregnancy body mass index. For women who were overweight before pregnancy (BMI of 25 to 29.9), the target is 15 to 25 pounds total. For women with a BMI of 30 or higher, the recommendation is 11 to 20 pounds. Women at a normal weight are generally advised to gain 25 to 35 pounds.
These aren’t arbitrary numbers. They reflect the balance between supporting fetal growth and avoiding complications like gestational diabetes and hypertension that can lead to medically necessary early delivery. Your provider can help you track your gain and adjust your nutrition if you’re falling outside the recommended range.
Warning Signs to Act On
Even with every preventive measure in place, preterm labor can still happen. Knowing what to watch for means you can get help quickly, which can make a significant difference. The key warning signs include regular or frequent contractions or tightening of the uterus (these are often painless, which catches people off guard), a gush or slow trickle of fluid suggesting your water has broken, persistent low back pain, pelvic pressure that feels like the baby is pushing down, and a change in vaginal discharge.
If you notice any of these before 37 weeks, don’t wait to see if they go away. Early intervention when preterm labor begins can sometimes delay delivery long enough to give the baby critical extra time to develop.