Symptoms and Risk Factors of Preterm Birth
Many factors can cause or contribute to spontaneous premature delivery. Fetal fibronectin is the most powerful predictor of preterm birth <32 weeks compared to traditional risk factors.1
NIH preterm prediction study: Risk factors for preterm birth 1
Fetal fibronectin is the most powerful predictor of preterm birth <32 weeks.1
Who is at risk for preterm birth?
- Prior preterm birth — women with a prior preterm birth before 37 weeks have a rate of recurrent preterm birth as high as 55%.2 The risk of recurrent preterm birth rises with the number of prior preterm births.3,4 Risk also increases as the gestational age of the prior preterm birth decreases.3,4
- Short cervix — as the cervical length decreases, the relative risk of preterm birth increases. There is a 5-fold increase in risk of preterm delivery <35 weeks among women with a cervical length of 2.0 cm vs. women with a cervical length of 4.0 cm.5
- Multiples — another risk factor for preterm birth is having multiples. Between 1980 and 2004, the rates of twin births rose from 18.9 to 32.2 per 1000 live births.6 Approximately 60% of twin births occur <37 weeks, and 12% of twin births occur <32 weeks.7
- Symptoms — contractions, cramping, bleeding, and statements such as "I just don't feel good" are symptoms of preterm labor. In patients with symptoms plus a positive fFN test, 44.7% will deliver <37 weeks.8
Assessing the clinical relevance of risk factors
In an individual patient, some risk factors play a greater role than others. However, more than half of spontaneous preterm births occur in women who have no apparent risk factors,4 which makes it important to pay careful attention to symptoms that could signal preterm labor.
Interventional studies have not shown that eliminating single risk factors reduces the rate of preterm delivery. Rather, it appears that spontaneous prematurity is a syndrome involving a combination of factors that arise and combine in different ways over the course of a pregnancy.4
The role of fetal fibronectin in predicting preterm birth
Fetal fibronectin is the single, common biochemical marker for all four mechanisms of preterm birth. Fetal fibronectin can often be detected before the biophysical markers.
View a diagram of major pathways for preterm birth
Risk factors for preterm labor
References
- 1. Goldenberg RL, Iams JD, Mercer BM, et al. The preterm prediction study: the value of new vs. standard risk factors in predicting early and all spontaneous preterm births. Am J Public Health. 1998;88:233-38.
- 2. Meis PJ, Klebanoff M, Thom E, et al. Prevention of recurrent preterm delivery by 17 alpha-hydroxyprogesterone caproate. N Engl J Med. 2003;348:2379-85.
- 3. Adams MM, Elam-Evans LD, Wilson HG, Gilbertz DA. Rates of and factors associated with recurrence of preterm delivery. JAMA. 2000;283:1591-96.
- 4. Mercer BM, Goldenberg RL, Moawad AH, et al. The preterm prediction study: effect of gestational age and cause of preterm birth on subsequent obstetric outcome. Am J Obstet Gynecol. 1999;181:1216-21.
- 5. Iams JD, Goldenberg RL, Meis PJ, et al. The length of the cervix and the risk of spontaneous premature delivery. N Engl J Med. 1996;334(9):567-72.
- 6. Martin JA, Hamilton BE, Sutton PD, et al. Births: Final data for 2004. National Vital Statistics Reports. NCHS. Sept 2006;55(1):1-102.
- 7. Singer E, Pilpel S, Bsat F, et al. Accuracy of fetal fibronectin to predict preterm birth in twin gestations with symptoms of labor. Obstet Gynecol. 2007 May;109(5):1083-87.
- 8. Peaceman AM, Andrews WW, Thorp JM, et al. Fetal fibronectin as predictor of preterm birth in patients with symptoms: A multicenter trial. Am J Obstet Gynecol. 1997;177:13-18.