Fetal Fibronectin

You may start hearing more about a substance (and a test) called fetal fibronectin. Fibronectin is a protein that resides in the cells where the fetal membranes come in contact with the uterus. The fetal membranes are also known as the “bag of waters”, or amniotic sac. No one is certain what role fibronectin plays in the fetal membranes. It appears that it may be some sort of biological glue. In any case, fibronectin is there near the membranes (there are 2 membranes, the amnion and the chorion), and in most pregnancies stays put until labor begins.

Shortly before labor, larger amounts of fibronectin are released and can be detected in the upper vagina near the cervix. Scientists have known about fibronectin for some time now, but only recently has someone come up with a reliable, “affordable” test which can be used in the clinical setting.

Midwives and doctors currently must use a “wait and see” strategy to determine if a woman who is having contractions is actually in labor. Not all women who are experiencing uterine contractions will go into labor in the short run……that’s how the term, “false labor”, came into existence. The only practical way to diagnosis whether a contracting woman is in labor is to examine the cervix (for dilatation and effacement) and wait to see if it dilated and effaced. That’s OK to do with a woman at term (that is, at the end of her pregnancy). However, what if the baby is still premature? If one could predict premature labor which was about to become a premature delivery, preparations could be made to assure that the birth occurs in a setting which is best for a premature baby.

Well, there’s now an “affordable” test that can be used in the clinical setting (as opposed to a laboratory) to detect fetal fibronectin. There are some problems, however, with the interpretation of the test. It’s not 100% accurate at diagnosing which women will give birth prematurely (few medical tests are). The absence of fibronectin is a fairly good indicator that a woman is not about to give birth (only one women in 125 with a negative test will give birth within 14 days). However, a positive test still only predicts far less than half of those women who go into labor soon (1 out of 6 women with a positive test will give birth within 14 days). The test is performed much like a Pap smear…..but has to be done before the doctor, nurse or midwife examines the cervix.

How can a test that is not very accurate help in the management of preterm labor? Often, a midwife or doctor has to make a difficult decision with women who appear to be in premature labor. Ideally, the premature baby should be born in a hospital with the best equipment and staff to handle a premature baby. Not all hospital are equipped to care for these tiny babies. In fact, most are not. If a midwife or doctor could predict which women will give birth prematurely, it would help contain the high cost of ambulance and helicoptor transfers to the “Level 3” hospitals (and the costs of caring for a woman who is NOT about to give birth).

So, any test that would help diagnose premature birth is an extremely valuable test. On the verge of the new millenium, that test is the fetal fibronectin test. It’s not perfect, but it’s the best we have right now. If your doctor or midwife decides to use this test during your pregnancy, you must listen carefully to what it CAN and CANNOT do for you.