Diagnosis of Preterm Labor and Delivery

The doctor will ask about your symptoms and health history. Some things that may be done are:

Pelvic Exam

The pelvic exam is done to see if the cervix has begun to dilate or if it is too thin. A woman may be in preterm labor if dilation has started. It is measured in 0 to 10 cm (centimeters). Birth often happens after the cervix has dilated to 10 cm. Thinning of the cervix is called effacement. It is given as a percent. A woman who is 50% effaced has a cervix that has thinned to half of its original thickness. When the cervix is fully dilated and effaced, then the head can descend with pushing.

Fetal Fibronectin

During the pelvic exam, the doctor may swab the vagina to test for fetal fibronectin (fFN). This acts as a glue to attach the amniotic sac to the lining of the uterus. It is normal for fFN to be in vaginal secretions for the first 22 weeks of pregnancy. If fFN is in secretions past weeks 22 to 34, then the glue may be breaking down earlier than it should. This may be a sign of preterm labor.


An ultrasound may also be done. This test uses sound waves to create an image of the uterus, the fluid around the baby, and the baby. It can also be used to check the length of the cervix.


A tocometer is a machine that tracks how often and how long contractions are. This can help diagnose preterm labor.



American College of Obstetricians and Gynecologists’ Committee on Practice Bulletins—Obstetrics. Practice Bulletin No. 171: Management of Preterm Labor. Obstet Gynecol. 2016 Oct;128(4):e155-64, reaffirmed 2018.
How do health care providers diagnose preterm labor? National Institute of Child Health and Human Development website. Available at:
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Accessed July 31, 2020
Premature labor. American Pregnancy Association website. Available at:
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Preterm labor. EBSCO DynaMed website. Available at: https://www.dynamed.com/condition/preterm-labor. Accessed July 31, 2020.
Preterm labor and birth. The American College of Obstetricians and Gynecologists website. Available at: https://www.acog.org/patient-resources/faqs/labor-delivery-and-postpartum-care/preterm-labor-and-birth. Accessed July 31, 2020.
Preterm labor and birth. National Institute of Child Health and Human Development website. Available at: https://www.nichd.nih.gov/health/topics/preterm/Pages/default.aspx. Accessed July 31, 2020.
Last reviewed March 2020 by EBSCO Medical Review Board Beverly Siegal, MD, FACOG
Last Updated: 2/24/2021

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