To help evaluate a pregnant woman's risk of preterm delivery
Fetal Fibronectin (fFN)
When you are 22 to 35 weeks pregnant and are having symptoms of premature labor; sometimes if you are at high risk, such as if you have had a previous preterm delivery or have a short cervix
A cervical or vaginal fluid sample
Fetal fibronectin (fFN) is a glycoprotein that can be used to help predict the short term risk of premature delivery. fFN is produced at the boundary between the amnionic sac (which surrounds the baby) and the lining of the mother's uterus (the decidua) in an area called the uteroplacental (or choriodecidual) junction. Fetal fibronectin is largely confined to this junction and is thought to help maintain the integrity of the boundary. fFN is normally detectable in cervicovaginal fluid during early pregnancy and, in a normal pregnancy, it is no longer detectable after 24 weeks. However, it reappears and is again detectable after about 36 weeks.
According to the American College of Obstetricians and Gynecologists (ACOG), a normal pregnancy is 40 weeks, with a woman going into labor between 37 and 42 weeks. Finding fFN in cervicovaginal fluids after 36 weeks is not unusual as it is often released by the body as it gets ready for childbirth. The elevated fFN found in vaginal fluids early in pregnancy may simply reflect the normal growth and establishment of tissues at the uteroplacental junction, with levels falling when this phase is complete. What is known is that fFN should not be detectible between 22 and 35 weeks of pregnancy. Elevated levels during this period reflect a disturbance at the uteroplacental junction and have been associated with an increased risk of preterm labor and delivery.
How is the sample collected for testing?
A swab is used to take a sample of cervical or vaginal fluid from the posterior portion of the vagina or from the area just outside the opening of the cervix.
Is any test preparation needed to ensure the quality of the sample?
Anything that physically disturbs the cervix or uterus has the potential to elevate fFN levels. Therefore, cervicovaginal fluid samples should be collected before any physical examinations. Lubricants, lotions, soaps, and douches should be avoided. Semen may contain enough fFN to create a positive test result, so sexual intercourse should also be avoided within 24 hours of sample collection.
How is it used?
Fetal fibronectin (fFN) is used to test pregnant women who are between 22 weeks and 35 weeks of gestation and are having symptoms of premature labor. The test helps predict the likelihood of premature delivery.
Many pregnant women experience symptoms that suggest preterm labor. These may include uterine contractions, changes in vaginal discharge, backaches, pelvic pressure, cramping, and cervical dilation. However, not all symptomatic women will actually have a preterm delivery. The majority will go on to deliver at term.
Unfortunately, while premature births can have successful endings, serious complications are possible when a baby leaves the womb early. Babies who are less than 37 weeks old frequently have difficulty breathing and feeding. Their lungs and other organs are immature and do not function normally, and the strain on them can cause persistent health problems. The more premature the newborn, the more likely it is that he or she will experience complications.
If a health practitioner thinks that a woman might deliver early, she will consider treatments designed to delay delivery. These treatments can have unwanted side effects, however, so, knowing whether or not a woman is likely to deliver prematurely helps in the decision on the best course of action. The fFN test is a relatively noninvasive tool that can help distinguish between those women who are likely to deliver shortly and those who are not.
The fFN test should only be used for those who:
- Have intact amniotic membranes
- Have a cervix that has not dilated more than 3 centimeters
- Have only slight vaginal bleeding
- Do not have cervical cerclage (a cervix that has been sewn shut during pregnancy to help keep the baby in the uterus; used when someone has a weak cervix)
The fFN test is not recommended for screening asymptomatic, low-risk women.
When is it ordered?
The fFN test is ordered when a woman is 22 weeks to 35 weeks pregnant and has symptoms of preterm labor. These may include uterine contractions, a change in vaginal discharge, backache, abdominal discomfort, pelvic pressure, and/or cramping.
The fFN test may be repeated after 2 weeks if the first fFN is negative and labor symptoms persist beyond the next 7 to 14 days. The test may therefore be repeated several times since each test result is valid for the following 7 to 14 days.
The fFN test is not meant to be used for women with placental abruption (premature detachment of the placenta), premature rupture of membranes, placenta previa (a placenta attached to the lower portion of the uterus), or moderate to heavy vaginal bleeding.
What does the test result mean?
A positive fFN result is not very predictive of preterm labor and delivery. However, a negative fFN result is highly predictive that preterm delivery will not occur within the next 2 weeks.
In other words, when the fFN test is performed on a symptomatic woman who meets the qualifying conditions, a negative test result means that there is a less than 1% chance of her having a premature delivery within the next 2 weeks. A health practitioner will also use other tests and her clinical expertise to evaluate each individual situation.
Since there are risks associated with treating a woman for premature labor (in anticipation of a premature delivery), a negative fFN can reduce unnecessary hospitalizations and drug therapies.
A positive fetal fibronectin test is less specific. It is associated with an increased risk for preterm delivery and with neonatal complications, but it will not tell a woman's health care provider whether or not she will deliver early. A positive test suggests the need to monitor a symptomatic woman more closely.
Is there anything else I should know?
If the risk for preterm delivery is high, extra measures can be taken to delay delivery for as long as possible and to help prepare the fetus for birth. Tocolytic agents can be used to help inhibit uterine contractions, the hormone progesterone can help to reduce the incidence of preterm birth in women who have a history of preterm births, and corticosteroids can be given to the woman to help mature the baby's lungs. In addition, the woman may be put on bedrest or hospitalized and may be transferred to a medical institution that has the expertise and equipment to handle premature births.
What are the risk factors for preterm labor and delivery?
There are a number of risk factors, but the greatest risk seems to be to women who:
- Have had a previous preterm delivery
- Are pregnant with multiples
- Have a short cervix
Other risk factors include:
- Late or no prenatal care
- Having certain chronic conditions, such as high blood pressure or diabetes
- Having certain problems with your uterus, cervix, or placenta
- Having certain infections during the pregnancy
- Being underweight or overweight before pregnancy, or gaining too little or too much weight during pregnancy
- Smoking, drinking alcohol, or using illicit drugs
- Being the victim of abuse or other stressful events
- Having multiple miscarriages
Maternal age (less than 18 or more than 40 years) and race seem also to be factors, with African American women at significantly higher risk than Caucasian or Hispanic women.
Why not test after 35 weeks?
Because fFN levels normally rise as full term delivery nears and because a baby born after 34 to 35 weeks of gestation is less likely to suffer premature complications, testing this late in pregnancy is not generally recommended.
Can preterm labor and delivery be prevented?Generally no, but the use of tocolytic agents, given to inhibit uterine contractions, may delay delivery. In the meantime, corticosteroids can be given to help the fetal lungs mature and prevent neonatal respiratory distress syndrome, and time is gained to transfer the woman to a tertiary treatment center.
What other tests are used to help determine the risk of preterm delivery?