To diagnose preterm labor, your doctor will review your symptoms and do a pelvic exam. Your doctor may also do some testing and monitoring.

Pelvic Exam

The pelvic exam is done to see if your cervix has begun to dilate or to thin. If dilation has begun, you may be in preterm labor. Dilation is measured in centimeters from 0-10. Birth usually occurs when the cervix has dilated to 10 centimeters. Thinning is also called effacement, which is reported as a percent. If you are “50% effaced,” your cervix has thinned to half of its original thickness. When you reach “100% effaced,” the cervix is completely thinned and ready for a vaginal delivery. Sometimes, the length of the cervix is assessed by an ultrasound measurement.

Fetal Fibronectin

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 preterm labor.

The presence of fFN (positive test result) is not a good predictor of whether you are at risk of preterm birth. If fFN is not present, your pregnancy is likely to continue at least another two weeks. The absence of fFN (negative test result) is a good predictor that you are not at risk of a preterm birth at this time.

Other Monitoring

A uterine activity monitor can measure and time your contractions. The monitor is strapped around your belly and is worn at home.

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 inside. Your doctor can then examine this image.