Obstetrics & Gynecology:
Change in Mononuclear Leukocyte Responsiveness in Midpregnancy and Subsequent Preterm Birth
Harper, Margaret MD, MSc; Li, Liwu PhD; Zhao, Yuan MSc; Klebanoff, Mark A. MD, MPH; Thorp, John M. Jr MD; Sorokin, Yoram MD; Varner, Michael W. MD; Wapner, Ronald J. MD; Caritis, Steve N. MD; Iams, Jay D. MD; Carpenter, Marshall W. MD; Peaceman, Alan M. MD; Mercer, Brian M. MD; Sciscione, Anthony DO; Rouse, Dwight J. MD; Ramin, Susan M. MD; Anderson, Garland D. MD; for the Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD) Maternal-Fetal Medicine Units (MFMU) Network
Departments of Obstetrics and Gynecology, Wake Forest University Health Sciences, Winston-Salem, North Carolina, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, Wayne State University, Detroit, Michigan, University of Utah Health Sciences Center, Salt Lake City, Utah, Columbia University, New York, New York, University of Pittsburgh, Pittsburgh, Pennsylvania, The Ohio State University, Columbus, Ohio, Women and Infants Hospital, Brown University, Providence, Rhode Island, Northwestern University, Chicago, Illinois, Case Western Reserve University-MetroHealth Medical Center, Cleveland, Ohio, Drexel University College of Medicine, Philadelphia, Pennsylvania, the University of Alabama at Birmingham, Birmingham, Alabama, the University of Texas Health Science Center at Houston, Houston, Texas, and the University of Texas Medical Branch, Galveston, Texas; the Division of Inflammation Biology and Immunology, Department of Biological Sciences, Virginia Polytechnic Institute and State University, Blacksburg, Virginia; the George Washington University Biostatistics Center, Washington, DC; and the Eunice Kennedy Shriver National Institute of Child Health and Human Development, Bethesda, Maryland.
Corresponding author: Margaret Harper, MD, MSc, Mountain Area Health Education Center, 119 Hendersonville Road, Asheville, NC 28803; e-mail: firstname.lastname@example.org.
The project described was supported by grants from the Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD) (HD27860, HD27917, HD40560, HD34208, HD40485, HD21410, HD27915, HD40500, HD40512, HD40544, MO1-RR-000080, HD34136, HD27869, HD40545, HD36801, HD19897) and does not necessarily represent the official views of the NICHD or the National Institutes of Health.
Presented at the 31st Annual Meeting of the Society for Maternal-Fetal Medicine, February 7-12, 2011, San Francisco, California.
Financial Disclosure The authors did not report any potential conflicts of interest.
The authors thank Karen Dorman, RN, MS, for protocol development and coordination between clinical research centers, Elizabeth Thom, PhD, for protocol and data management and statistical analysis, and Catherine Y. Spong, MD, for protocol development and oversight.
*For a list of other members of the NICHD MFMU, see the Appendix online at http://links.lww.com/AOG/A357.
Dr. Spong and Dr. Rouse, Associate Editors of Obstetrics & Gynecology, were not involved in the review or decision to publish this article.
OBJECTIVE: To estimate the associations of change in immune response with preterm delivery, omega-3 supplementation, and fish diet.
METHODS: This was an ancillary study to a randomized trial of omega-3 fatty acid supplementation for the prevention of recurrent preterm birth. In vitro maternal peripheral blood mononuclear leukocyte production of the anti-inflammatory cytokine, interleukin-10, and the proinflammatory cytokine, tumor necrosis factor-α, in response to stimulation with lipopolysaccharide, was measured at 16–22 weeks of gestation (baseline) and again at 25–28 weeks of gestation (follow-up) among women with prior spontaneous preterm birth. Changes in concentrations from baseline to follow-up ([INCREMENT]) were compared separately among groups defined by gestational age category at delivery, fish diet history, and omega-3 compared with placebo treatment assignment with Kruskal-Wallis tests.
RESULTS: Interleukin-10 [INCREMENT] differed by gestational age category among 292 women with paired assays. Concentrations increased less in women delivering between 35 and 36 6/7 weeks of gestation (48.9 pg/mL) compared with women delivering at term (159.3 pg/mL) and decreased by 65.2 pg/mL in women delivering before 35 weeks of gestation (P=.01). Tumor necrosis factor-α Δ also differed by gestational age category among 319 women, but the pattern was inconsistent. Those delivering between 35 and 36 6/7 weeks of gestation exhibited decreased concentrations of tumor necrosis factor-α at follow-up compared with baseline (−356.0 pg/mL); concentrations increased among women delivering before 35 weeks of gestation and those delivering at term, 132.1 and 86.9 pg/mL (P=.03). Interleukin-10 Δ and tumor necrosis factor-α Δ were unaffected by either omega-3 supplementation or fish diet.
CONCLUSION: Recurrent preterm birth was associated with decreased peripheral blood mononuclear leukocyte production of interleukin-10 in response to a stimulus during the second trimester.
CLINICAL TRIAL REGISTRATION: ClinicalTrials.gov, www.clinicaltrials.gov, NCT00135902.
LEVEL OF EVIDENCE: II
A causal link between an inflammatory response and preterm delivery is well established.1–4 Proinflammatory cytokines and chemokines may be central in the final common pathway initiating labor as a result of not only infection, but also decidual hemorrhage, uteroplacental ischemia, cervical disease, or immunologic phenomenon.4–9 The Th2 anti-inflammatory cytokine, interleukin-10 (IL-10), has a significant role in the maintenance of pregnancy.3,10,11 Treatment with IL-10 in animal models of intraamniotic infection reduces IL-1β-induced uterine contractions, amniotic fluid concentrations of tumor necrosis factor-α (TNF-α) and leukocyte counts and improves pregnancy outcomes.12–14 In human studies, peripheral blood mononuclear leukocyte production of IL-10 has been found to be higher in the first trimester but lower at term when compared with levels in nonpregnant control patients suggesting that downregulation of IL-10 occurs as part of the inflammatory process necessary for term labor.15 The role of change in regulation of anti-inflammatory or proinflammatory cytokine production in response to an inflammatory stimulus across gestation in preterm birth has not been examined.
The innate immune response to a stimulus, including the balance between proinflammatory and anti-inflammatory cytokines, may alter disease severity; this response may vary between individuals because of genetic or environmental factors including dietary exposures such as omega-3 fatty acids.16–20 We conducted this study to estimate the associations of change in immune response with preterm delivery, omega-3 supplementation, and fish diet. We selected a priori TNF-α as the proinflammatory and IL-10 as the anti-inflammatory cytokine for study based on their functions in inflammation activation and resolution as well as preterm labor. Prior studies have demonstrated an effect of omega-3 fatty acids on peripheral blood mononuclear leukocyte production of TNF-α and IL-10.20–22
PATIENTS AND METHODS
The cohort consisted of women from 13 Eunice Kennedy Shriver National Institute of Child Health and Human Development Maternal-Fetal Medicine Units Network centers enrolled in the randomized trial of omega-3 fatty acid supplementation to prevent recurrent preterm birth, registered at ClinicalTrials.gov (NCT00135902) between January 2005 and October 2006. The methods and results of the trial have previously been published.23 Inclusion criteria were a documented history of at least one prior singleton preterm delivery between 20 0/7 and 36 6/7 weeks of gestation after spontaneous preterm labor or preterm premature rupture of the membranes and a current singleton pregnancy. The study was approved by the institutional review board of each clinical site and of the data coordinating center. Women gave written informed consent for study participation and were enrolled between 16 and 21 6/7 weeks of gestation. Participants were randomized to receive either a daily supplement of 2,000 mg of long chain omega-3 polyunsaturated fatty acids or matching placebo capsules. All participants received weekly injections of 17 alpha-hydroxyprogesterone caproate (250 mg) because of their obstetric histories of spontaneous preterm delivery.24 There was no difference in the rate of preterm birth between the omega-3 and placebo groups. Fish diet histories were assessed at baseline enrollment. The four items in the food frequency questionnaire are dark meat fish, canned tuna, other fish, and shellfish.25
Blood samples were collected between 16 and 22 weeks of gestation before starting study drug and again at the follow-up visit between 25 and 28 weeks of gestation for cytokine analysis. None of the women were in labor or prelabor when the samples were collected. Samples were shipped overnight on ice to a central laboratory (Dr. Li, Division of Inflammation Biology and Immunology, Department of Biological Sciences, Virginia Polytechnic Institute and State University, Blacksburg, Virginia). Peripheral blood mononuclear leukocytes were isolated from heparinized blood by Isolymph sedimentation followed by centrifugation for 5 minutes at 200×g. The pellet was resuspended at a final concentration of 5×106 cells/mL in complete RPMI 1640 medium supplemented with 10% fetal bovine serum. Cells were cultured at 37°C with 5% CO2 for 24 hours. Tumor necrosis factor-α and IL-10 secretion in cell supernatants were analyzed using enzyme-linked immunosorbent assay kits according to the manufacturer's instructions. The assays were performed concomitantly in separate cell culture after incubating with 100 ng/mL lipopolysaccharide (Escherichia coli 0111:B4). Detection limits were 1 pg/mL for IL-10 and 2 pg/mL for TNF-α.26,27 Samples with concentrations below the limit of detection or otherwise out of range were excluded from the analysis, which examined change over time.
We used Wilcoxon rank-sum and χ2 tests as appropriate to compare demographic and clinical variables of women included in this ancillary study with those of women in the trial but excluded from the ancillary study because of lack of paired samples from baseline and follow-up. Change in inflammatory response to a stimulus was assessed by computing the change in concentrations of IL-10 and TNF-α in the cell supernatants (after lipopolysaccharide stimulation minus unstimulated) from baseline (16–22 weeks of gestation) to follow-up (25–28 weeks of gestation) in paired samples from the same patients. The change in concentrations of IL-10 and TNF-α was compared between groups defined by gestational age at delivery (37 weeks of gestation or greater, 35 through 36 6/7 weeks of gestation, and less than 35 weeks of gestation), fish diet history (less than one fish meal per week and one fish meal per week or more), and treatment assignment with Kruskal-Wallis tests.28 We chose a priori three gestational age groups because infection and inflammation are more frequently identified in early compared with late preterm births. The number of extreme preterm births, less than 28 weeks of gestation, with paired baseline and follow-up samples was too small for meaningful analysis as a separate group, one patient for IL-10 and two patients for TNF-α. Fish diet history categories were selected based on our previously reported analysis that showed an association between low dietary intake of fish and preterm birth in the randomized trial cohort.29 Multivariable logistic analysis adjusting for treatment assignment, earliest gestational age of prior preterm delivery, number of prior preterm deliveries, smoking, race and ethnicity, body mass index, and clinical center was conducted to test the relationship between preterm birth and fish diet history for the women with paired cytokine measurements included in this ancillary study. To adjust for multiple pairwise comparisons of cytokine concentrations among the three groups defined by gestational age at delivery, we used a P value of .017; otherwise, a P<.05 was selected as indicative of significance. All comparisons were two-sided.
Among the 852 women enrolled in the trial, 343 had paired cytokine measurements for IL-10, TNF-α, or both (Fig. 1). The median age, number of prior preterm births and distribution by race, smoking history, or fish dietary intake did not differ between those women who had paired measurements and those who did not. Women with paired measurements were more likely than women without paired measurements to be in the omega-3 treatment group (Table 1). The rate of preterm birth less than 37 weeks of gestation for women with paired measurements was 36.7% and was not different from the rate for women in the trial without paired measurements, 41.7% (P=.15).
Peripheral blood mononuclear leukocyte production of both cytokines increased after lipopolysaccharide stimulation compared with unstimulated levels. The median (interquartile range) increase in pg/mL was 992.8 (259.9–1,553.5) for TNF-α and 1,079.5 (303.9–2,419.6) for IL-10.
A total of 292 women had paired assays for IL-10 and 319 women had paired assays for TNF-α. Table 2 shows the median change with range and interquartile range from baseline to follow-up in concentrations (lipopolysaccharide stimulated minus unstimulated) for IL-10 and TNF-α for the three groups defined by gestational age at delivery. The median change in concentrations in IL-10 was different between the three groups (P=.01). The increase in IL-10 was less in women delivering at 35–36 weeks of gestation (48.9 pg/mL) compared with women delivering at term (159.3 pg/mL) and decreased from baseline to follow-up among women delivering before 35 weeks of gestation (median decrease of 65.2 pg/mL) (Table 2). The pairwise comparisons revealed the changes in concentrations were different between those delivering before 35 weeks of gestation compared with those delivering at term (P=.01). The change in median concentrations in TNF-α from baseline to follow-up also differed among the three groups defined by gestational age at delivery (P=.03), but the pattern was not consistent. Women delivering at 35–36 weeks of gestation had a drop in concentrations from baseline to follow-up (median decrease of 356.0 pg/mL). The median increase from baseline to follow-up among women delivering at term was 86.9 pg/mL; women delivering before 35 weeks of gestation also had an increase, 132.1 pg/mL (Table 2). The pairwise comparisons revealed the changes in concentrations were different between those delivering at 35–36 weeks of gestation compared with those delivering at term (P=.01).
Similar to the findings in the trial of 852 women, the rate of preterm birth in this ancillary study of 343 women varied by fish diet history. The rate of preterm birth at less than 37 weeks of gestation was 33.7% among those who ate at least one fish meal per week and 44.4% among those who ate less than one fish meal per week (P=.004, relative risk 0.76, 95% confidence interval [CI] 0.63–0.92). This association remained after controlling for treatment assignment, earliest gestational age of prior preterm delivery, number of prior preterm deliveries, smoking, race and ethnicity, body mass index, and clinical center (P=.03, odds ratio 0.68, 95% CI 0.48–0.96). We hypothesized that modulation of the inflammatory response may be a mechanism by which fish diet reduces preterm birth; however, there was no difference in the change in concentrations from baseline to follow-up for IL-10 or TNF-α between the two groups defined by dietary fish intake, less than one fish meal per week compared with at least one fish meal per week (Table 3). Our previous analysis of the association between fish diet and preterm birth showed a U-shaped pattern with probability of preterm birth decreasing with increasing fish intake but then increasing again. The protective effect of dietary fish was not observed in women eating four or more fish meals per week.29 Therefore, we also estimated the association between change in IL-10 and TNF-α concentrations among three fish diet groups: less than one meal per week, one to three meals per week, and four or more meals per week. There were no differences in these cytokine measurements among these three groups (data not shown) (IL-10, P=.58; TNF-α, P=.26). There were no differences in change in concentrations from baseline to follow-up for IL-10 or TNF-α between the omega-3 and placebo treatment groups (Table 3).
In this cohort of women with a prior spontaneous preterm delivery, we observed a decrease in LPS-stimulated peripheral blood mononuclear leukocyte production of IL-10 across the second trimester in women destined to deliver before 35 weeks of gestation. Women who subsequently delivered at term demonstrated an increase in IL-10 production and, although women delivering late preterm also had increased IL-10 production, the increase was less than among those delivering at term. It is believed that IL-10 plays a role in the maintenance of pregnancy and downregulation of IL-10 favors an inflammatory state.15,30,31 Interleukin-10 can block preterm labor induced by intrauterine infusion of lipopolysaccharide in rodents13 and IL-1β-induced preterm labor in primates.12 In a study of seven women either in the first trimester or at term before labor and seven age-matched nonpregnant control participants, peripheral blood mononuclear leukocyte production of IL-10 was higher than control participants in the first trimester but dropped to nonpregnant levels at term leading the investigators to hypothesize that withdrawal of anti-inflammatory agents, including anti-inflammatory cytokines, occurs to accelerate an inflammatory process necessary for term labor.15 Our data suggest this process may occur prematurely in women destined to deliver before term.
The study results did not support our hypothesis that the different effects of fish diet and omega-3 supplementation on preterm birth may be the result of differences in modulating the immune response. Our results are in agreement with those from a randomized clinical trial in pregnant women for primary allergy prevention conducted in Sweden. Among 145 women, lipopolysaccharide-induced TNF-α and IL-10 secretion from whole blood cultures was not different between those receiving 2.7 g of omega-3 polyunsaturated fatty acid supplementation daily and those receiving placebo.32 Although some studies in nonpregnant individuals, cell cultures, and animal models have reported a suppressive effect of omega-3 fatty acid supplementation on peripheral blood mononuclear leukocyte production of TNF-α and a stimulatory effect on production of IL-10,20–22 the majority of intervention studies in humans have found no effect of omega-3 supplementation or fish consumption on cytokines or other biomarkers of inflammation.33–39
Strengths of our study include a well-characterized, large cohort of women at high risk for preterm birth. We examined the response to an inflammatory stimulus with measurement of both an anti-inflammatory and a proinflammatory cytokine over time in the second trimester with paired samples.
The weaknesses of the study must be acknowledged. The study included women with a prior preterm delivery; therefore, the results may not be generalizable to other obstetric patients. All women received 17 alpha-hydroxyprogesterone caproate and it is unclear what effect this may have had on our study results. Progesterone is an immunomodulator at the maternal-fetal surface, affecting production of proinflammatory cytokines by macrophages and altering T-cell clone cytokine secretion in favor of IL-10.40–42
The role of activation of the maternal inflammatory response in the preterm parturition syndrome continues to be investigated. Our data suggest a role of premature downregulation of IL-10 production and may have implications for treatment; however, other studies across a wider gestational age range are needed to confirm these results. Study of subgroups such as women with a shortened cervical length in the midtrimester, women with chronic bleeding in pregnancy, and women with multifetal pregnancies might offer new insight about the preterm parturition syndrome in different clinical situations.
1. Gomez R, Ghezzi F, Romero R, Munoz H, Tolosa JE, Rojas I. Premature labor and intra-amniotic infection. Clinical aspects and role of cytokines in diagnosis and pathophysiology. Clin Perinatol 1995;22:281–342.
2. Keelan JA, Blumenstein M, Helliwell RJ, Sato TA, Marvin KW, Mitchell MD. Cytokines, prostaglandins and parturition—a review. Placenta 2003;24:S33–46.
3. Romero R, Espinoza J, Gonçalves LF, Kusanovic JP, Friel L, Hassan S. The role of inflammation and infection in preterm birth. Semin Reprod Med 2007;25:21–39.
4. Bastek JA, Gómez LM, Elovitz MA. The role of inflammation and infection in preterm birth. Clin Perinatol 2011;38:385–406.
5. Darby MI, Caritis SN, Shen-Schwartz S. Placental abruption in the preterm gestation: an association with chorioamnionitis. Obstet Gynecol 1989;74:88–92.
6. Lockwood CJ, Toti P, Arcuri F, Paidas M, Buchwalder L, Krikum G, et al.. Mechanisms of abruption-induced premature rupture of the fetal membranes: thrombin-enhanced interleukin-8 expression in term decidua. Am J Pathol 2005;167:1443–9.
7. Romero R, Gonzalez R, Sepulveda W, Brandt F, Ramirez M, Sorokin Y, et al.. Infection and labor: VIII. Microbial invasion of the amniotic cavity in patients with suspected cervical incompetence: prevalence and clinical significance. Am J Obstet Gynecol 1992;167:1086–91.
8. Bytautiene E, Romero R, Vedernikoy YP, El-Zeky F, Saade GR, Garfield RE. Induction of premature labor by allergic reaction and prevention by histamine H1 receptor antagonist. Am J Obstet Gynecol 2004;191:1356–61.
9. Peltier MR. Immunology of term and preterm labor. Reprod Biol Endocrinol 2003;1:122.
10. Krasnow JS, Tollerud DJ, Naus G, DeLoia JA. Endometrial Th2 cytokine expression throughout the menstrual cycle and early pregnancy. Hum Reprod 1996;11:1747–54.
11. Wegmann TG, Lin H, Guilbert L, Mosmann TR. Bidirectional cytokine interactions in the maternal-fetal relationship: is successful pregnancy a Th2 phenomenon? Immunol Today 1993;14:353–6.
12. Sadowsky DW, Novy MF, Witkin SS, Gravett MG. Dexamethasone or interleukin-10 blocks interleukin-1 beta-induced uterine contractions in pregnant rhesus monkeys. Am J Obstet Gynecol 2003;188:252–63.
13. Terrone DA, Rinehart BK, Granger JP, Barrilleaux PS, Martin JN Jr, Bennett WA. Interleukin-10 administration and bacterial endotoxin-induced preterm birth in a rat model. Obstet Gynecol 2001;98:476–80.
14. Rodts-Palenik S, Wyatt-Ashmead J, Pang Y, Thigpen B, Cal Z, Rhodes P, et al.. Maternal infection-induced white matter injury is reduced by treatment with interleukin-10. Am J Obstet Gynecol 2004;191:1387–92.
15. Hanna N, Hanna I, Hleb M, Wagner E, Dougherty J, Balkundi D, et al.. Gestational age-dependent expression of IL-10 and its receptor in human placental tissues and isolated cytotrophoblasts. J Immunol 2000;164:5721–8.
16. Crider KS, Whitehead N, Buus RM. Genetic variation associated with preterm birth: a HuGE review. Genet Med 2005;7:593–604.
17. 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.
18. Pontes-Arruda A, Aragao AM, Albuquerque JD. Effects of enteral feeding with eicosapentaenoic acid, gamma-linolenic acid, and antioxidants in mechanically ventilated patients with severe sepsis and septic shock. Crit Care Med 2006;34:2325–33.
19. Marik PE, Zaloga GP. Immunonutrition in critically ill patients: a systematic review and analysis of the literature. Intensive Care Med 2008;34:1980–90.
20. Hao W, Wong OY, Liu X, Lee P, Chen Y, Wong KK. ω-3 fatty acids suppress inflammatory cytokine production by macrophages and hepatocytes. J Pediatr Surg 2010;45:2412–8.
21. Meydani SN, Endres S, Woods MM, Goldin BR, Soo C, Morrill-Labrode A, et al.. Oral (n-3) fatty acid supplementation suppresses cytokine production and lymphocyte proliferation: comparison between young and older women. J Nutr 1991;121:547–55.
22. Endres S, Ghorbani R, Kelley VE, Georgilis K, Lonnemann G, van der Meer JWM, et al.. The effect of dietary supplementation with n-3 polyunsaturated fatty acids on the synthesis of interleukin-1 and tumor necrosis factor by mononuclear cells. N Engl J Med 1989;320:265–71.
23. Harper M, Thom E, Klebanoff M, Thorp J Jr, Sorokin Y, Varner M, et al.. Omega-3 fatty acid supplementation to prevent recurrent preterm birth. Obstet Gynecol 2010;115:234–42.
24. Meis PJ, Klebanoff M, Thom E, Dombrowski MP, Sibai B, Moawad AH, et al.. National Institute of Child Health and Human Development Maternal-Fetal Medicine Units Network. Prevention of recurrent preterm delivery by 17 alpha-hydroxyprogesterone caproate. N Engl J Med 2003;348:2379–85.
25. Willet WC, Sampson L, Stamper MJ, Rosner B, Bain C, Witschi J, et al.. Reproducibility and validity of a semiquantitative food frequency questionnaire. Am J Epidemiol 1985;122:51–65.
26. Li L, Cousart S, Hu J, McCall CE. Characterization of interleukin-1 receptor associated kinase in normal and endotoxin-tolerant cells. J Biol Chem 2000;275:23340–5.
27. Li T, Hu J, Li L. Characterization of Tollip protein upon lipopolysaccharide challenge. Mol Immunol 2004;41:85–92.
28. Zimmerman DW. A note on consistency of non-parametric rank tests and related rank transformations. Br J Math Stat Psychol 2012;65:122–44.
29. Klebanoff MA, Harper M, Lai Y, Thorp J Jr, Sorokin Y, Varner MW, et al.. Fish consumption, erythrocyte fatty acids, and preterm birth. Obstet Gynecol 2011;117:1071–7.
30. Hanna N, Bonifacio L, Weinberger B, Reddy P, Murphy S, Romero R, et al.. Evidence for interleukin-10 mediated inhibition of cyclo-oxygenage-2 expression and prostaglandin production in preterm human placenta. Am J Reprod Immunol 2006;55:19–27.
31. 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.
32. Warstedt K, Furuhjelm C, Duchén K, Fälth-Magnusson K, Fageräs M. The effects of omega-3 fatty acid supplementation in pregnancy on maternal eicosanoid, cytokine and chemokine secretion. Pediatr Res 2009;66:212–7.
33. Vega-Lopez S, Kaul N, Devaraj S, Cai RY, German B, Jialal I. Supplementation with omega3 polyunsaturated fatty acids and all-rac alpha-tocopherol alone and in combination failed to exert an anti-inflammatory effect in human volunteers. Metabolism 2004;53:236–40.
34. Fujioka S, Hamazaki K, Itomura M, Huan M, Nishizawa H, Sawazaki S, et al.. The effects of eicosapentaenoic acid-fortified food on inflammatory markers in healthy subjects—a randomized, placebo controlled, double-blind study. J Nutr Sci Vitaminol 2006;52:261–5.
35. Lee KW, Blann AD, Lip GY. Effects of omega-3 polyunsaturated fatty acids on plasma indices of thrombogenesis and inflammation in patients post-myocardial infarction. Thromb Res 2006;118:305–12.
36. Browning LM, Krebs JD, Moore CS, Mishra GD, O'Connell MA, Jebb SA. The impact of long chain n-3 polyunsaturated fatty acid supplementation on inflammation, insulin sensitivity and CVD risk in a group of overweight women with an inflammatory phenotype. Diabetes Obes Metab 2007;9:70–80.
37. Schiano V, Laurenzano E, Brevetti G, De Maio JI, Lanero S, Scopacasa F, et al.. Omega-3 polyunsaturated fatty acid in peripheral arterial disease: effect on lipid pattern, disease severity, inflammation profile, and endothelial function. Clin Nutr 2008;27:241–7.
38. Yusof HM, Miles EA, Calder PC. Influence of very long-chain n-3 fatty acids on plasma markers of inflammation in middle-aged men. Prostaglandins Leukot Essent Fatty Acids 2008;78:219–28.
39. de Roos B, Mavrommatis Y, Brouwer IA. Long-chain n-3 polyunsaturated fatty acids: new insights into mechanisms relating to inflammation and coronary heart disease. Br J Pharmacol 2009;158:413–28.
40. Stites DP, Siiteri PK. Steroids as immunosuppressants in pregnancy. Immunol Rev 1983;75:117–38.
41. Siiteri PK, Stites DP. Immunologic and endocrine interrelationships in pregnancy. Biol Reprod 1982;26:1–14.
42. Hansen PJ. Regulation of uterine immune function by progesterone–lessons from the sheep. J Reprod Immunol 1998;40:63–79.
Supplemental Digital Content
© 2013 The American College of Obstetricians and Gynecologists
ACOG MEMBER SUBSCRIPTION ACCESS
If you are an ACOG Fellow and have not logged in or registered to Obstetrics & Gynecology, please follow these step-by-step instructions to access journal content with your member subscription.