Fetal Fibronectin Screening During Pregnancy: When Might You Need It?

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Have you heard of fFN?

This test can be used as a screening tool to estimate your personal risks of preterm labor. In certain scenarios it may be very helpful to you; but on the other hand, fFN should be used with care. Read on!

fFN stands for fetal fibronectin and is a commercially available test. Your doctor or midwife may have this test in their office or use it in the hospital. fFN is FDA approved, which means there are enough data to support the use of it with confidence!

fFN is collected by swabbing the area behind the cervix. The test measures a protein released from the layer between the chorion and amnion in the uterus. In a normal pregnancy, the protein isn’t released until close to full-term, so if this protein is present at high levels before 35 weeks gestational age, it is called a POSITIVE test and increases the risk of preterm delivery.

Premature delivery occurs in about 12% of pregnancies. Some cases of early delivery are due to medical conditions such as preeclampsia, but spontaneous premature labor accounts for many of these.

Here are some cases where fFN may be useful. You could even ask your provider for this test.

1. You are working hard all day at about 28 weeks pregnancy and start feeling contractions after lunch. By 3pm it really hurts! You call your midwife and she directs you to come to the hospital. The nurse places you on a monitor and you are correct: you are contracting every three minutes. The midwife sees you and BEFORE she checks your cervix, she asks if you have had intercourse in the last 24 hours or any bleeding. You have not, so she explains she will collect the fFN and then check your cervix (fFN has to be collected before a cervical exam, and isn’t reliable if you have had sex or bleeding in the past 24 hours). The fFN will come back in about an hour and in the meantime, she wants you to drink fluids (which you realize you have not been doing enough of while working all day!). Your cervix is 1cm dilated and soft. The contractions are already better now that you are sitting down…
2. You had a “short cervix” noted on ultrasound when your doctor wanted to see how big your baby had grown. The cervical length measurement has been the same for a few weeks, but your doctor is trying to decide whether to give you steroids to help the fetal lungs mature. At 32 weeks, you are having contractions so she performs the fFN test.
3. Your first pregnancy was complicated, and you delivered twins at 26 weeks without much warning! Your cervix has been followed carefully this time and it has been normal (more than 3 cm). Now at 28 weeks, you are getting nervous and having contractions frequently although each time you are seen, your doctor tells you that your cervix feels normal and closed. You start having increased discharge and some contractions, so your doctor sees you in the office and finds your cervix to be 2cm dilated at 30 weeks. The fFN was collected prior to the exam and your doctor is trying to decide if you should be admitted to the hospital.

So, when should fFN be used?

I collect a fFN sample on all of my patients who are contracting before 35 weeks (although I don’t send every test to the lab to get a result). Here’s why: fFN is a very good test for the NEGATIVE predictive value which means if the test is collected and it is negative, the chances of early delivery are extremely low (<1%). However, it has very poor positive predictive value, which means that the chance of early delivery is higher when the test is POSITIVE (29%) but still not very likely. Often in the above cases, the test will help as follows:

1. Should a patient be admitted to the hospital?
2. Should a patient be given betamethasone (steroids) to help for the baby’s lungs mature?
3. Should a patient be given medications (all having risks) to stop contractions?

Generally, fFN should be used in circumstances that would help make the decisions described above, and not as a screening tool in a patient without any symptoms. It can be used in patients with a short cervix and no symptoms, with twins, and with patients who have a history of early delivery but the predictive value of the test isn’t very good.

I send the test to the lab (I collect it before I check my patient’s cervix, afterward it’s too late) only if the result will change a clinical decision. For example, I had a patient recently whose cervix was 1cm dilated at 28 weeks. I decided that if the fFN was positive, I would admit her to the hospital to receive steroids; if it was negative, I would send her home and see her in the office in a week to re-check. The fFN was negative, so I sent her home, confident that she wouldn’t go into preterm labor.

One approach you may consider, if your doctor or midwife discusses fFN with you, is to ask her how the result will change management.

So don’t go contracting prematurely, but if you do, discuss the fFN with your midwife or doctor.

Tamara Takoudes, MD

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