Premature birth risk factors

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [5]


Risk Factors

There are many different factors which may contribute to a preterm birth.

Factors related to maternal disease or condition that have been shown to increase the risk of preterm birth, with associated odds ratio (OR) when known include:

  • Chromosomal abnormalities; Dr. Aaron Caughey, a perinatologist at UCSF, states..."'s important to note that the majority of miscarriages - up to 80 percent - happen due to chromosomal abnormalities that have nothing to do with the mother's behavior. The last thing women who have had miscarriages need to do is blame themselves...." -SF Chronicle
  • age > 35 (OR = 1.8) [3]
  • age < 18 (OR = 3.4) [3]
  • short cervix [1] (the strongest predictor of premature birth)[4][5][6]
  • maternal diabetes [7]
  • Short interpregnancy interval (IPI) has been associated with subsequent premature delivery.[8] However, when the analysis is performed within women who have had at least three pregnancies (two intervals) and each woman serves as her own control, increased risk is found when the first pregnancy was preterm[9] but not among unselected women.[10]

Whether or not urinary tract infections directly cause preterm birth is uncertain, however, it is known that urinary tract infections increase pre-eclampsia which as stated above increases the risk of preterm birth. Sexually transmitted disease STD, Beta Strep, kidney disease, and uterine infections are also suspected of increasing the risk of preterm birth.

Adequate maternal nutrition is important to fetal development and a diet low in saturated fat and cholesterol may help reduce the risk of a preterm delivery. [13]

Factors related to pregnancy history that have been shown to increase the risk of preterm birth include:

  • prior preterm delivery (OR = 2.79)
  • prior induced abortion (OR = 1.6)
  • antepartum hemorrhage / vaginal bleeding during labor
  • prior miscarriage [1]

Multiple pregnancies (twins, triplets, etc.) are another significant factor in preterm birth. The March of Dimes Multicenter Prematurity and Prevention Study found that 54% of twins were delivered preterm vs. 9.6% of singleton births. [14]

Women who have tried to conceive for more than a year before getting pregnant are at a higher risk for premature birth. A recent study done by Dr. Olga Basso of the University of Aarhus in Denmark and Dr. Donna Baird of the U.S. National Institute of Environmental Health Sciences suggests that women who had difficulty conceiving were about 40 percent higher risk of preterm birth than those who had conceived easily.

Finally, the use of tobacco and alcohol during pregnancy also increases the chance of preterm delivery. Tobacco is the most commonly abused drug during pregnancy and also contributes significantly to low birth weight delivery.[15] [16]


  1. 1.0 1.1 1.2 Goldenberg RL, Iams JD, Mercer BM; et al. (1998). "The preterm prediction study: the value of new vs standard risk factors in predicting early and all spontaneous preterm births. NICHD MFMU Network". Am J Public Health. 88 (2): 233–8. PMID 9491013.
  2. Bánhidy F, Acs N, Puhó EH, Czeizel AE (2007). "Pregnancy complications and birth outcomes of pregnant women with urinary tract infections and related drug treatments". Scand. J. Infect. Dis. 39 (5): 390–7. doi:10.1080/00365540601087566. PMID 17464860. Text "1B69BA326FFE69C3F0A8F227DF8201D0" ignored (help)
  3. 3.0 3.1 Martius JA, Steck T, Oehler MK, Wulf KH (1998). "Risk factors associated with preterm (<37+0 weeks) and early preterm birth (<32+0 weeks): univariate and multivariate analysis of 106 345 singleton births from the 1994 statewide perinatal survey of Bavaria". Eur. J. Obstet. Gynecol. Reprod. Biol. 80 (2): 183–9. PMID 9846665.
  4. To MS, Skentou CA, Royston P, Yu CKH, Nicolaides KH. Prediction of patient-specific risk of early preterm delivery using maternal history and sonographic measurement of cervical length: a population-based prospective study. Ultra Obstet Gynecol 2006; 27: 362–367.
  5. Fonseca et al. Progesterone and the risk of preterm birth among women with a short cervix. NEJM 2007; vol 357, no 5, pg 462-469.
  6. Romero R. Prevention of spontaneous preterm birth: the role of sonographic cervical length in identifying patients who may benefit from progesterone treatment. Ultrasound Obstet Gynecol 2007; 30: 675-686. free download
  7. Rosenberg TJ, Garbers S, Lipkind H, Chiasson MA (2005). "Maternal obesity and diabetes as risk factors for adverse pregnancy outcomes: differences among 4 racial/ethnic groups". Am J Public Health. 95 (9): 1545–51. doi:10.2105/AJPH.2005.065680. PMID 16118366.
  8. Conde-Agudelo A, Rosas-Bermúdez A, Kafury-Goeta AC (2006). "Birth spacing and risk of adverse perinatal outcomes: a meta-analysis". JAMA. 295 (15): 1809–23. doi:10.1001/jama.295.15.1809. PMID 16622143.
  9. Koullali B, Kamphuis EI, Hof MH, Robertson SA, Pajkrt E, de Groot CJ; et al. (2016). "The Effect of Interpregnancy Interval on the Recurrence Rate of Spontaneous Preterm Birth: A Retrospective Cohort Study". Am J Perinatol. doi:10.1055/s-0036-1584896. PMID 27367283.
  10. Ball SJ, Pereira G, Jacoby P, de Klerk N, Stanley FJ (2014). "Re-evaluation of link between interpregnancy interval and adverse birth outcomes: retrospective cohort study matching two intervals per mother". BMJ. 349: g4333. doi:10.1136/bmj.g4333. PMC 4137882. PMID 25056260.
  11. Dole N, Savitz DA, Hertz-Picciotto I, Siega-Riz AM, McMahon MJ, Buekens P (2003). "Maternal stress and preterm birth". Am. J. Epidemiol. 157 (1): 14–24. PMID 12505886.
  12. Jeffcoat, Marjorie K., Nico C. Geurs, Michael S. Reddy, Suzanne P. Cliver, Robert L. Goldenberg, and John C. Hauth. "Periodontal Infection and Preterm Birth." The Journal of the American Dental Association 132 (2001): 875-880. 25 April 2007 [1].
  13. "Cholesterol Lowering Diet for Pregnant Women May Help Prevent Preterm Birth." BMJ: British Medical Journal 331 (2005): 1093. 1 May 2007 [2].
  14. Gardner MO, Goldenberg RL, Cliver SP, Tucker JM, Nelson KG, Copper RL (1995). "The origin and outcome of preterm twin pregnancies". Obstet Gynecol. 85 (4): 553–7. doi:10.1016/0029-7844(94)00455-M. PMID 7898832.
  15. Shiono, Patricia H., Mark A. Klebanoff, Robert P. Nugent, Mary F. Cotch, Diana G. Wilkins, Douglas E. Rollins, Christopher J. Carey, and Richard E. Behrman. "Fetus-Placenta-Newborn: the Impact of Cocaine and Marijuana Use on Low Birth Weight and Preterm Birth: a Multicenter Study." American Journal of Obsetrics and Gynecology 172 (1995): 19-27. 1 May 2007 [3].
  16. Parazzini, F, L. Chatenoud, M. Surace, L. Tozzi, B. Salerio, G. Bettoni, and G. Benzi. "Moderate Alcohol Drinking and Risk of Preterm Birth." European Journal of Clinical Nutrition 57 (2003): 1345. 1 May 2007 [4].