Some women who have a positive fetal fibronectin test result deliver within 2 to 4 weeks of the positive fetal fibronectin but your actual delivery time after the test can vary.
A positive fetal fibronectin result means that fetal fibronectin is present in your cervical secretions.
If you have a positive result between weeks 22 and 34, you're at increased risk of premature birth within seven days.
It's not mandatory that a mother with a positive fetal fibronectin test would have a premature delivery.
There's around a 17-41% chance of delivery within 2 weeks after a positive fetal fibronectin test.
Combination of fFN and cervical length does not seem to increase the predictive accuracy of both tests taken separately.
A positive fFN testing increases the individual PTB probability from 7.5% to 66.1%, due to its high positive likelihood ratio of 24, whereas a negative test decreases it to 2.4%.
It is believed that fetal fibronectin keeps the amniotic sac attached to the uterine lining.
In practice, a positive test result indicates that the mother is at increased risk of preterm birth during the ensuing seven days.
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.