What is a Fetal Fibronectin Test?

A fetal fibronectin test is done to determine whether there is any fetal fibronectin (fFN) present in a pregnant woman's cervical secretions. This substance is a type of protein. If the test is positive, this means that the woman may give birth soon. It is often performed to evaluate the probability of a preterm, or premature, birth.

Fetal fibronectin is the substance that holds the amniotic sac to the lining of the uterus. The amniotic sac cushions the fetus. If fFN is present in the cervical secretions, this indicates that the sac has been disturbed. It is not a definite indicator of preterm birth, however. On the other hand, if there is no fFN evident, the expectant mother is safe to assume that she will not go into labor for at least another week.

Women who anticipate undergoing a fetal fibronectin test should refrain from sexual intercourse for 24 hours. They should also inform their doctors if they experience vaginal bleeding. In such a case, the fetal fibronectin test may need to be postponed. If the amniotic sac is ruptured, labor is imminent and the test is no longer necessary.

The fetal fibronectin test requires a cervical swab. This simple procedure is very similar to a Pap smear. The patient will lie on her back and a speculum will be inserted into her vagina. A doctor will then insert a cotton swab to collect a small sample of cervical material.

Sometimes, the physician may decide to do a vaginal ultrasound after performing the fetal fibronectin test. This allows the doctor to check the length of the cervix. If the patient is close to labor, this measurement will often be smaller than normal. The ultrasound is taken with a slender instrument placed into the vagina. Sound waves are sent to a monitor and converted into images for analysis.

Results from the fetal fibronectin test are typically available within 24 hours. These results aid the physician in making recommendations to the expectant mother. The patient may need bed rest for the remainder of her pregnancy. Sometimes, even if the fFN test results are negative, the doctor may recommend increased rest, depending on the patient's health.

To help protect the health of the fetus, the patient may take temporary medication to reduce the risk of a premature birth. These drugs are called tocolytic, or labor-suppressing medications. In other cases, the physician may administer a series of steroid injections. These shots help increase the rate at which the fetus's lungs mature. Expectant mothers should carefully follow the doctor's instructions to help prevent a preterm birth.