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11 Things That can Cause Preterm Labor and Early Delivery

Jennifer Lincoln, MD, IBCLC, Board Certified OB/GYN
January 3, 2019 . 14 min read

1. Uterine stretching

Factors that stretch the uterus can cause contractions, which in turn can trigger early labor. Such factors include having multiple babies, excessive amniotic fluid, fibroids in the uterine wall, and having a large baby.

2. A short cervix

A short cervix can trigger early labor as the baby grows. Generally, “short” is defined as less than 2.5 centimeters long. Your doctor can usually see this during ultrasound.

3. Abnormal uterus structure

Anything that results in an abnormally shaped uterus—including developmental issues or the presence of a septum in the uterine wall—can trigger early labor.

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5. Closely spaced pregnancies

Having babies closely together is a risk factor for preterm labor. Doctors aren’t sure why, but moms who get pregnant within 18 months of their previous pregnancy have higher rates of preterm labor and delivery.

6. History of preterm pregnancy

A history of preterm delivery increases your chances of having another preterm labor and delivery. Your doctor should know about any previous preterm birth and ideally you’d have a preconception visit. Progesterone injections are sometimes used to reduce the risk of preterm delivery.

7. Bleeding

There are a number of reasons you might experience bleeding during pregnancy, but whatever the cause, blood in the uterus can trigger early labor.

8. Smoking during pregnancy

Among its many potential harms, smoking (or abusing any substances) during pregnancy can increase the risk of going into labor early and delivering a preterm baby.

9. Being African American

For reasons we don’t entirely understand, African American women in the United States are almost twice as likely to experience preterm birth as other women. This pattern is unique to the United States, so researchers think it must be a combination of environment and other factors.

10. Untreated infections

Infections of almost any type—STDs, dental, urinary tract, etc.—increase your risk of preterm birth. Make sure to let your doctor know of any unusual symptoms and keep up with regular dental visits.

11. Weighing too little before pregnancy

Women with a lower body mass index (less than 19.8 BMI) are more likely to go into early labor and deliver their babies early. If you can, schedule a preconception visit with your doctor to talk about ways to gain healthy weight before getting pregnant.

12. Using fertility treatments

Couples who conceive using fertility treatments, including in vitro fertilization, are more likely to experience preterm birth. The best option is to work closely with your doctor and monitor your symptoms carefully.


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

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