To diagnose preterm labor, your doctor will review your symptoms and medical history. Your doctor may do or advise one or more of the following:
The pelvic exam is done to see if the cervix has begun to dilate or if it is too thin. If dilation has begun, you may be in preterm labor. Dilation is measured in centimeters from 0-10. Birth usually occurs after the cervix has dilated to 10 centimeters. Thinning of the cervix is called effacement. It is reported as a percent. If you are 50% effaced, the cervix has thinned to half of its original thickness. When the cervix is fully dilated and effaced, then the head can descend with pushing.
A tocometer is a machine that measures uterine contractions. A tocometer is a monitoring device that tracks the frequency and length of contractions. Over a short period of time, a pattern emerges that can help your doctor with a diagnosis.
During the pelvic exam, your doctor may swab your cervix to test for fetal fibronectin (fFN). fFN acts as a glue to attach the amniotic sac to the lining of the uterus. It is normal for fFN to be in cervical secretions for the first 22 weeks of pregnancy. However, if fFN is present in the outer cervix beyond weeks 22-34, this glue may be breaking down earlier than it should. fFN may be a sign of impending preterm labor.
The presence of fFN (positive test result) is not a good predictor of whether you are at risk of preterm birth. However, the absence of fFN (negative test result) is a good predictor that you are not at risk of a preterm birth at this time. Your pregnancy is likely to continue for at least another 2 weeks.
An ultrasound may also be done. This test uses sound waves to create an image of your uterus, the fluid around the baby, and the baby. It can also be used to determine cervical length.
American College of Obstetricians and Gynecologists, Committee on Practice Bulletins—Obstetrics. ACOG practice bulletin no. 127: Management of preterm labor. Obstet Gynecol. 2012;119(6):1308-1317.
How do health care providers diagnose preterm labor? National Institute of Child Health and Human Development website. Available at: http://www.nichd.nih.gov/health/topics/preterm/conditioninfo/Pages/diagnosed.aspx. Updated January 31, 2017. Accessed March 7, 2018.
Premature labor. American Pregnancy Association website. Available at: http://americanpregnancy.org/labor-and-birth/premature-labor. Updated March 10, 2017. Accessed March 7, 2018.
Preterm labor. EBSCO DynaMed Plus website. Available at:http://www.dynamed.com/topics/dmp~AN~T115273/Preterm-labor. Updated January 2, 2018. Accessed March 7, 2018.
Preterm (premature) labor and birth. The American College of Obstetricians and Gynecologists website. Available at: http://www.acog.org/~/media/For%20Patients/faq087.pdf?dmc=1&ts=20130423T0923201528. Updated November 2016. Accessed March 7, 2018.
Last reviewed March 2018 by EBSCO Medical Review Board Beverly Siegal, MD, FACOG Last Updated: 3/15/2015