Third Trimester Tests

Fetal Fibronectin (FFN) Test

Content Provided by March of Dimes

The fetal fibronectin (FFN) test measures the levels of FFN in secretions from a pregnant woman's vagina and cervix. According to the American College of Obstetricians and Gynecologists (ACOG), the FFN test may be useful for some pregnant women with symptoms of preterm labor (labor before 37 completed weeks of pregnancy) to help predict their risk of premature delivery (1).

What is fetal fibronectin?

FFN is a protein produced during pregnancy. It acts as a biological glue, attaching the fetal sac to the uterine lining. FFN normally is present in cervico-vaginal secretions up to 22 weeks of pregnancy and again at the end of the last trimester (1 to 3 weeks before labor). FFN usually cannot be detected between 24 and 34 weeks of pregnancy (5 1/2 to 8 1/2 months).

What is the FFN test?

Health care providers give the FFN test to women between 24 and 34 weeks of pregnancy. The presence of FFN during these weeks, along with symptoms of labor, suggests that the "glue" may be disintegrating ahead of schedule and alerts health care providers to a possibility of premature labor and delivery.

Providers use a cotton swab to collect samples of cervico-vaginal secretions during a speculum examination (similar to a Pap smear). Results usually are available within 24 hours. The result is either positive (FFN is present) or negative (FFN is not present).

What do FFN test results mean?

Most women with symptoms of preterm labor go on to deliver at term, even without treatment (2). The FFN test can help predict which symptomatic women have a reduced risk of premature labor and delivery. Fewer than 5 percent of women with symptoms of preterm labor who have a negative FFN test result deliver within the next 2 weeks (1). Identifying symptomatic women who have a reduced risk of premature delivery is the most valuable use of this test because these women often can avoid unnecessary medical interventions, such as bedrest, prenatal corticosteroids, hospitalization and labor-suppressing (tocolytic) medications (1,3).

Positive FFN test results in women with symptoms of preterm labor are less reliable. However, positive results allow health care providers and pregnant women to take preventive measures to delay labor as long as possible and to consider labor-suppressing medications.

Group B Streptococcus (GBS)

Your vagina and rectum will be swabbed and the results cultured to see if you have strep. Group B Streptococcus is part of the normal bacteria on the skin of 10 to 30 percent of American women. It does not cause illness in adults, but can cause devastating illness in newborns. The Centers for Disease Control and Prevention recommends all pregnant women be tested between 35 and 37 weeks. If you test positive, have had a urinary tract infection with GBS during this pregnancy, or a previous infant with GBS disease, you will be treated with intravenous (IV) antibiotics when you are in labor. If your water breaks or you go into labor before 37 weeks, before your test results are available or before you have been tested, you will also receive IV antibiotics. If you have questions, please ask your health care provider.


Your blood is drawn. This test is for anemia and may show that you need more iron.

Non-Stress Test

Devices are placed on your abdomen to monitor your baby's heartbeat. This test gives your health care provider information about your baby's health. The primary goal of the test is to measure the heart rate of the fetus in response to its own movements.