While it is true that we don’t completely understand why labor really begins, there are some things that can make your chance of giving birth preterm — or before 37 weeks gestation — much more likely. Here’s a list of issues that can lead to delivering too soon:

1. Anything that stretches the uterus. The uterus is a muscle, and when it is overstretched it can contract more. Sometimes, these contractions can lead to preterm labor. Situations where the uterus may be more distended include carrying more than one baby, have an excessive amount of amniotic fluid, having large fibroids in the wall of the uterus, or being pregnant with a very large baby (which sometimes happens when women have poorly controlled diabetes, for example).

2. Having a short cervix. The cervix is what helps hold the uterus closed, and a short cervix (generally defined as less than 2.5 centimeters long) can increase your risk of giving birth too early.

3. Structurally abnormal uterus. A few conditions can lead to a woman having a uterus with an abnormal shape (such as having a uterus that is only partially developed or that has a septum running down the middle), which puts a baby at risk for delivering early. Luckily, most of these can be identified on ultrasound or through other imaging studies.

4. Very closely spaced pregnancies. Women who get pregnant again less than 18 months after giving birth are at an increased risk for preterm birth. We aren’t quite sure why this happens, but it may be that the woman’s body has not completely recovered (physically and nutritionally) from having just been pregnant.

5. A previous preterm pregnancy. Having given birth prematurely before (and not for a reason such as being induced early, but rather going into preterm labor on your own) is one of the biggest risk factors for delivering early again. If you fall into this category, a preconception visit is key to help reduce your risk of delivering too soon. Your doctor will likely recommend early screening of things such as your cervical length, as well as possibly recommending progesterone injections (17-hydroxyprogesterone caproate) to decrease your risk of preterm birth.

6. Bleeding. Bleeding in pregnancy can be from multiple issues, but blood in the uterus can irritate it. And when a muscle like the uterus gets irritated, it can contract, possibly leading to preterm labor.

7. Smoking and drug use during pregnancy. Smoking and substance abuse are not good for pregnant women and their babies for so many reasons; one of those is that they can increase your risk for delivering too soon. The good news is that unlike other risk factors, these can be changed. 

8. Ethnic background. African American women in the U.S. experience preterm birth twice as much as women in other ethnic groups in this country. We aren’t sure why this is exactly because this disparity is not seen in other countries, but it is possibly from a combination of genetic and environmental issues.

9. Untreated infections. Untreated urinary tract infections, sexually transmitted infections, and even dental infections may increase a woman’s risk for experiencing preterm birth. We aren’t totally sure of the link, but this is why it’s always important to mention any abnormal symptoms to your doctor or midwife and continue regular dental care, even when you are pregnant.

10. Weighing too little before getting pregnant. Women who have a low body mass index (less than 19.8) are at an increased risk for preterm birth. If you are in this category, it’s best to make a preconception visit to discuss healthy ways to put on the pounds before trying to conceive!

11. Using fertility treatments to conceive. Babies conceived using fertility treatments such as in vitro fertilization (IVF) are at increased for being born early.


  • Delivering preterm is defined as giving birth at less than 37 weeks of pregnancy.
  • Preterm birth can be the result of multiple risk factors.
  • Some risk factors, such as smoking and having too closely spaced pregnancies, can be modified to remove your risk of an early delivery.

Last reviewed by Jennifer Lincoln, MD, IBCLC. Review Date: January 2019


  1. The American College of Obstetricians and Gynecologists. Practice Bulletin #130: Prediction and prevention of preterm birth. October 2012.
  2. SG Gabbe et al. Obstetrics: Normal and problem pregnancies. 5th ed.
  3. The American College of Obstetricians and Gynecologsits. Patient FAQ#87: Preterm (premature) labor and birth. September 2015.


  1. Great article! Especially as we honor World Prematurity Day, it’s important for women to know their risk factors for premature labor as some are within their power to control.


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