The concept that genetic differences can modify the transcription of cytokines in response to an inflammatory stimulus has led investigators to explore the association between selected SNPs in candidate cytokine genes and rates of preterm delivery. In this cohort of women with at least one previous spontaneous preterm delivery, a homozygous genotype for guanine>adenine substitution at the −308 position in the promoter region of the TNF-α gene was associated with a significantly shorter length of gestation. Carriage of this allele is known to result in increased production of TNF-α and an altered inflammatory response is believed to increase the risk of extreme preterm birth.28–31 The association we observed between this genotype and spontaneous extreme preterm birth at less than 28 weeks of gestation therefore is intriguing. Because of the infrequency of this genotype and the outcome of extreme preterm birth, the number of observations available for assessing this association was small. We are not aware of any other studies that have examined this association.
Not all studies have reported a significant association between maternal genotype for TNF-α −308 and preterm birth.19,35 Differences in study results may be attributable to study design, sufficient power, or method of analysis. We used a cohort rather than a case-control study design. We assessed the associations between genotype and length of gestation rather than the outcome of preterm birth at less than 37 weeks of gestation. Also, most other studies have combined heterozygous (TNF-α −308GA) individuals with those homozygous (TNF-α −308AA) for the minor allele because of small numbers of homozygous AA individuals.
There are several strengths of this study. The conduct of the clinical trial provided opportunity for this prospective ancillary study in a well-characterized cohort with a high rate of preterm delivery. Gestational dating was set by uniform criteria that incorporated ultrasound assessment before 22 weeks of gestation. This is one of the largest cohorts of pregnant women genotyped for the TNF-α −308 SNP reported to date. Few studies have included more women with the homozygous minor genotype. A case-control study from Nashville included 534 women with TNF-α −308 genotyping and only nine with the AA genotype. This series was published with a meta-analysis of five previous studies, all with sample size smaller than ours, and the homozygous minor genotype was not analyzed separately.36 One larger cohort from Austria included 1,652 women, with 41 with the AA genotype; this group was at much lower risk, and hence the preterm birth rate was lower.37 We used Kaplan-Meier survival curves to assess the association between genotype and length of gestation. This may be a more appropriate model for assessing the genetic contribution to the complex trait of timing of parturition rather than the dichotomous outcome of term compared with preterm delivery. Although the cohort was at high risk, the TNF-α −308G>A allele and genotype frequencies for the cohort as a whole and by race were similar to previously published frequencies, and all three SNPs were in Hardy-Weinberg equilibrium.36,37
The limitations of this study must be considered in interpreting the results. All women received 17-α-hydroxyprogesterone caproate because of their previous pregnancy histories. It is not known what effect, if any, 17-α-hydroxyprogesterone caproate may have on gene transcription or the inflammatory response. The number of women with the TNF-α −308 AA genotype was small. We did not analyze fetal DNA. The relative contribution of the maternal and fetal genotypes to preterm birth has not yet been determined. Vaginal Gram stains were not available to correlate with genotypes and outcomes.
In conclusion, our results suggest polymorphism at the −308 position of the TNF-α promoter region which modulates gene transcription is associated with shorter gestation among women with at least one previous spontaneous preterm delivery. In addition, women with this genotype were at significantly increased risk for spontaneous extreme preterm delivery. Our findings support the concept that an altered inflammatory response predisposes to shorter gestation and extreme preterm birth.
1. Preterm birth: crisis and opportunity. Lancet 2006;369:339.
2. Romero R, Espinoza J, Kusanovic JP, Gotsch F, Hassan S, Erez O, et al. The preterm parturition syndrome. BJOG 2006;113(Suppl 3):17–42.
3. Dudley DJ. Pre-term labor: an intra-uterine inflammatory response syndrome? J Reprod Immunol 1997;36:93–109.
4. So T, Ito A, Sato T, Mori Y, Hirakawa S. Tumor necrosis factor-alpha stimulates the biosynthesis of matrix metalloproteinases and plasminogen activator in cultured human chorionic cells. Biol Reprod 1992;46:722–8.
5. Arechavaleta-Velasco F, Ogando D, Parry S, Vadillo-Ortega F. Production of matrix metalloproteinase-9 in lipopolysaccharide-stimultated human amnion occurs through autocrine and paracrine proinflammatory cytokine-dependent systems. Biol Reprod 2002;67:1952–8.
6. Friebe-Hoffmann U, Chiao JP, Rauk PN. Effect of IL-1beta and IL-6 on oxytocin secretion in human uterine smooth muscle cells. Am J Reprod Immunol 2001;46:226–31.
7. Rauk PN, Friebe-Hoffmann U, Winebrenner LD, Chiao JP. Interleukin-6 up-regulates the oxytocin receptor in cultured uterine smooth muscle cells. Am J Reprod Immunol 2001;45:148–53.
8. Sadowsky DW, Novy MJ, Witkin SS, Gravett MG. Dexamethasone or interleukin-10 blocks inerleukin-1beta-induced uterine contractions in pregnant rhesus monkeys. Am J Obstet Gynecol 2003;188:252–63.
9. Romero R, Espinoza J, Gonçalves LF, Kusanovic JP, Friel LA, Nien JK. Inflammation in preterm and term labour and delivery. Semin Fetal Neonatal Med 2006;11:317–26.
10. Goepfert AR, Goldenberg RL, Andrews WW, Hauth JC, Mercer B, Iams J, et al. The Preterm Prediction Study: association between cervical interleukin 6 concentration and spontaneous preterm birth. National Institute of Child Health and Human Development Maternal-Fetal Medicine Units Network. Am J Obstet Gynecol 2001;184:483–8.
11. Maymon E, Ghezzi F, Edwin SS, Mazor M, Yoon BH, Gomez R, et al. The tumor necrosis factor alpha and its soluble receptor profile in term and preterm parturition. Am J Obstet Gynecol 1999;181:1142–8.
12. Steinborn A, Günes H, Röddiger S, Halberstadt E. Elevated placental cytokine release, a process associated with preterm labor in the absence of intrauterine infection. Obstet Gynecol 1996;88:534–9.
13. Winkler M, Kemp B, Fischer DC, Maul H, Hlubek M, Rath W. Tissue concentrations of cytokines in the lower uterine segment during preterm parturition. J Perinat Med 2001;29:519–27.
14. Hillier SL, Witkin SS, Krohn MA, Watts DH, Kiviat NB, Eschenbach DA. The relationship of amniotic fluid cytokines and preterm delivery, amniotic fluid infection, histologic chorioamnionitis, and chorioamnion infection. Obstet Gynecol 1993;81:941–8.
15. Porter TF, Fraser AM, Hunter CY, Ward RH, Varner MW. The risk of preterm birth across generations. Obstet Gynecol 1997;90:63–7.
16. Mercer BM, Goldenberg RL, Moawad AH, Meis PJ, Iams JD, Das AF, et al. The preterm prediction study: effect of gestational age and cause of preterm birth on subsequent obstetric outcome. National Institute of Child Health and Human Development Maternal-Fetal Medicine Units Network. Am J Obstet Gynecol 1999;181:1216–21.
17. Bloom SL, Yost NP, McIntire DD, Leveno KJ. Recurrence of preterm birth in singleton and twin pregnancies. Obstet Gynecol 2001;98:379–85.
18. Bhattacharya S, Raja EA, Mirazo ER, Campbell DM, Lee AJ, Norman JE, et al. Inherited predisposition to spontaneous preterm delivery. Obstet Gynecol 2010;115:1125–33.
19. Roberts AK, Monzon-Bordonaba F, Van Deerlin PG, Holder J, Macones GA, Morgan MA, et al. Association of polymorphism within the promoter of the tumor necrosis factor alpha gene with increased risk of preterm premature rupture of the fetal membranes. Am J Obstet Gynecol 1999;180:1297–1302.
20. Simhan HN, Krohn MA, Zeevi A, Daftary A, Harger G, Caritis SN. Tumor necrosis factor-alpha promoter gene polymorphism−308 and chorioamnionitis. Obstet Gynecol 2003;102:162–6.
21. Reiman M, Kujari H, Ekholm E, Lapinleimu H, Lehtonen L, Haataja L, et al. Interleukin-6 polymorphism is associated with chorioamnionitis and neonatal infections in preterm infants. J Pediatr 2008;153:19–24.
22. Moore S, Ide M, Randhawa M, Walker JJ, Reid JG, Simpson NA. An investigation into the association among preterm birth, cytokine gene polymorphisms and periodontal disease. BJOG 2004;111:125–32.
23. Genç MR, Gerber S, Nesin M, Witkin SS. Polymorphism in the interleukin-1 gene complex and spontaneous preterm delivery. Am J Obstet Gynecol 2002;187:157–63.
24. Speer EM, Gentile DA, Zeevi A, Pillage G, Huo D, Skoner DP. Role of single nucleotide polymorphisms of cytokine genes in spontaneous preterm delivery. Hum Immunol 2006;67:915–23.
25. Harper M, Thom E, Klebanoff MA, Thorp J Jr, Sorokin Y, Varner MW, et al. Omega-3 fatty acid supplementation to prevent recurrent preterm birth: a randomized controlled trial. Obstet Gynecol 2010;115:234–42.
26. Dombrowski MP, Schatz M, Wise R, Momirova V, Landon M, Mabie W, et al. Asthma during pregnancy. Obstet Gynecol 2004;103:5–12.
27. Attia J, Ioannidis JP, Thakkinstian A, McEvoy M, Scott RJ, Minelli C, et al. How to use an article about genetic association: B: Are the results of the study valid? JAMA 2009;301:191–7.
28. Jeong P, Kim EJ, Kim EG, Byun SS, Kim CS, Kim WJ. Association of bladder tumors and GA genotype of −308 nucleotide in tumor necrosis factor-alpha promoter with greater tumor necrosis factor-alpha expression. Urology 2004;64:1052–6.
29. González S, Rodrigo L, Martínez-Borra J, López-Vázquez A, Fuentes D, Niño P, et al. TNF-alpha−308A promoter polymorphism is associated with enhanced TNF-alpha production and inflammation activity in Crohn's patients with fistulizing disease. Am J Gastroenterol 2003;98:1101–6.
30. Andrews WW. Cervicovaginal cytokines, vaginal infection, and preterm birth. Am J Obstet Gynecol 2004;190:1179.
31. Goldenberg RL, Hauth JC, Andrews WW. Intrauterine infection and preterm delivery. N Engl J Med 2000;342:1500–7.
32. Crider KS, Whitehead N, Buus RM. Genetic variation associated with preterm birth: a HuGE review. Genet Med 2005;7:593–604.
33. van Deventer SJ. Cytokine and cytokine receptor polymorphisms in infectious disease. Intensive Care Med 2000;26:S98–102.
34. Fishman D, Faulds G, Jeffery R, Mohamed-Ali V, Yudkin JS, Humphries S, et al. The effect of novel polymorphisms in the interleukin-6 (IL-6) gene on IL-6 transcription and plasma IL-6 levels, and an association with systemic-onset juvenile chronic arthritis. J Clin Invest 1998;102:1369–76.
35. Dizon-Townson DS, Major H, Varner M, Ward K. A promoter mutation that increases transcription of the tumor necrosis factor-alpha gene is not associated with preterm delivery. Am J Obstet Gynecol 1997;177:810–3.
36. Menon R, Merialdi M, Betrán AP, Dolan S, Jiang L, Fortunato SJ, Williams S. Analysis of association between maternal tumor necrosis factor-alpha promoter polymorphism (−308), tumor necrosis factor concentration, and preterm birth. Am J Obstet Gynecol 2006;195:1240–8.
37. Stonek F, Bentz EK, Hafner E, Metzenbauer M, Philipp K, Hefler LA, Tempfer CB. A tumor necrosis factor-alpha promoter polymorphism and pregnancy complications: results of a prospective cohort study in 1652 pregnant women. Reprod Sci 2007;14:425–9.