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The Enigma of Spontaneous Preterm Birth To the Editor: Preterm birth is not, as Muglia and Katz (Feb. 11 issue)1 conclude, an “enigma” justifying passionate enthusiasm for “further knowledge of the biology” and investment in “talented investigators from diverse disciplines [who] need to work together, sharing databases, biologic samples, and intellectual perspectives.”1 We need first of all to implement what we already understand about the preventable causes of preterm birth such as the extremes of maternal age, assisted-conception practices, cervical damage, domestic violence, and smoking. In most countries, 10 to 25% of pregnant women smoke. Smoking 10 cigarettes a day causes an increase in preterm birth that is three times as high as that among women who do not smoke. Nora Volkow, director of the National Institute of Drug Abuse, stated that “smoking during pregnancy is the single most preventable cause of illness and [death] among mothers and infants, yet cigarette use continues among pregnant women in the [United States].”2 In Europe, too, smoking during pregnancy is the condition that is most frequently associated with inadequate treatment and has the greatest, but avoidable, effect on perinatal morbidity and mortality.3 If more research is needed, it must concern how to improve the implementation of evidence-based care. Alain Braillon, M.D. Place Victor Pauchet Amiens, France
[email protected]
Susan Bewley, M.D. Guy’s and St. Thomas’ Hospital National Health Service Foundation Trust London, United Kingdom No potential conflict of interest relevant to this letter was reported. 1. Muglia LJ, Katz M. The enigma of spontaneous preterm
birth. N Engl J Med 2010;362:529-35. 2. Volkow ND. Smoking common during pregnancy, study shows. ScienceDaily. April 25, 2007. (Accessed May 7, 2010, at http://www .sciencedaily.com/releases/2007/04/070424180831.htm.) 3. Richardus JH, Graafmans WC, Verloove-Vanhorick SP, Mackenbach JP. Differences in perinatal mortality and suboptimal care between 10 European regions: results of an international audit. BJOG 2003;110:97-105.
To the Editor: The review of possible causes of spontaneous preterm delivery by Muglia and Katz opens the door for more fine-tuned investigations. However, we have three concerns. First, the in2032
ference that preterm birth may be evolutionarily advantageous was unsubstantiated. Second, race is not biologic; rather, it is a social construct.1 Third, preventing preterm births requires more than knowledge of the biology of human parturition. Epigenetic processes influenced by the social environment may contribute to the control of parturition.2 Reducing a high incidence of disease, particularly in the black population, requires intervention research into reduction of social stress at the population level.3,4 We agree that further investigation necessitates incorporation of multidisciplinary teams of investigators, and we suggest that these teams include social epidemiologists, medical anthropologists, environmental specialists, urban planners, and community representatives, in addition to the usual investigators. Yvonne W. Fry-Johnson, M.D., M.S.C.R. Morehouse School of Medicine Atlanta, GA
Diane L. Rowley, M.D., M.P.H. University of North Carolina at Chapel Hill Chapel Hill, NC No potential conflict of interest relevant to this letter was reported. 1. Blank RM, Dabady M, Citro CF, eds. Measuring racial dis-
crimination: panel on methods for assessing discrimination. Washington, DC: National Academies Press, 2004. 2. Lins RJ, Mitchell MD. Novel insights into the control of human pregnancy: potential role(s) for epigenetic regulation. Reprod Biol Insights 2008;1:3-8. 3. Rose G. Sick individuals and sick populations. Int J Epidemiol 1985;14:32-8. 4. Schwartz S, Diez-Roux AV. Commentary: causes of incidence and causes of cases — a Durkheimian perspective on Rose. Int J Epidemiol 2001;30:435-9.
To the Editor: Muglia and Katz highlight the increasing U.S. preterm birth rate and suggest similar trends in other high-income countries. They attribute these trends to social stress, infection and inflammation, and genetic factors. The trend in Japan may be uniquely different and may also offer alternative explanations for a complex process. While the preterm birth rate has also increased from 4.1% in 1980 to 5.8% in 2007, the birth rate of low-birth-weight infants has risen dramatically, from 5.2% in 1980 to 9.6% in 2007 (Table 1).1 The Japanese data on assisted reproduction are incomplete; however, the similarly significant increase in multiple pregnancies indicates that changing social factors (e.g., increasing age
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correspondence
Table 1. Low Birth Weight and Preterm Births in Japan.* Year
Birth Weight
