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Protective Effect of Breastfeeding in Postpartum Relapse Rate of Mothers With Multiple Sclerosis—Reply

Protective Effect of Breastfeeding in Postpartum Relapse Rate of Mothers With Multiple... In reply Dr Iorio and colleagues describe the results of a retrospective analysis that examined the relationship between exclusive breastfeeding and postpartum relapses in 23 women followed up at their center. Their results are remarkably similar to those we described1 and actually support, rather than contradict, our overall conclusions. They found that women in the NBF group were twice as likely to relapse in the postpartum year and did so sooner than women in the BF group (proportions of women with relapses in NBF and BF groups, 53% vs 25%, respectively). Their results failed to achieve statistical significance, but this is simply owing to low study power. The belief that failure to achieve statistical significance is proof of no effect is a well-recognized statistical fallacy.2 Hellwig et al also confirm our results. Based on a predominantly retrospective analysis of 156 women, they found a statistically significant 2.3-fold higher rate of relapse in those who do not breastfeed exclusively during the first 3 months after birth. Taken together, both articles support our findings and demonstrate the importance of distinguishing between exclusive and nonexclusive breastfeeding. While the magnitude of the effects reported by Iorio et al and Hellwig et al are large, they are smaller than the effect size we observed in our study. This difference is most likely owing to imprecision in how both groups measured exclusive breastfeeding and postpartum relapses. It is well known that relying on retrospective review of routine medical records to assess MS relapses results in underestimation of the true relapse rate; indeed, the number of postpartum relapses that Iorio et al observed is substantially fewer than what we1 and others3 have observed through protocol-driven prospective assessments. Retrospective assessment of exclusive breastfeeding is also subject to significant measurement error, likely because of societal pressure to breastfeed. In our prospective study, we found that some women who report regular use of formula during the first 2 months after birth later reported (1 year after birth) that they did not start formula until more than 2 months after birth. Both of these types of measurement error would reduce the size of the observed effect. Despite these methodological shortcomings, both groups were able to detect a clinically significant difference between women who breastfed exclusively and those who did not, though the small study by Iorio et al did not reach statistical significance. Thus, both data sets support the overall conclusions of our study and indicate that the true effect of exclusive breastfeeding is likely to be quite large. Future studies to confirm or refute this protective effect of exclusive breastfeeding should use rigorous, prospective methods to measure exclusive breastfeeding and postpartum relapse. Correspondence: Dr Langer-Gould, Departments of Research and Evaluation and Neurology, Kaiser Permanente Southern California, 100 S Los Robles, Fourth Floor, Pasadena, CA 91101 (annette.m.langer-gould@kp.org). Financial Disclosure: None reported. References 1. Langer-Gould AHuang SMGupta R et al. Exclusive breastfeeding and the risk of postpartum relapses in women with multiple sclerosis [published online ahead of print June 8, 2009]. Arch Neurol 2009;66 (8) 958- 963PubMedGoogle ScholarCrossref 2. Cox DR Statistical significance tests. Br J Clin Pharmacol 1982;14 (3) 325- 331PubMedGoogle ScholarCrossref 3. Confavreux CHutchinson MHours MMCortinovis-Tourniaire PMoreau TPregnancy in Multiple Sclerosis Group, Rate of pregnancy-related relapse in multiple sclerosis. N Engl J Med 1998;339 (5) 285- 291PubMedGoogle ScholarCrossref http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Archives of Neurology American Medical Association

Protective Effect of Breastfeeding in Postpartum Relapse Rate of Mothers With Multiple Sclerosis—Reply

Archives of Neurology , Volume 66 (12) – Dec 1, 2009

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Publisher
American Medical Association
Copyright
Copyright © 2009 American Medical Association. All Rights Reserved.
ISSN
0003-9942
eISSN
1538-3687
DOI
10.1001/archneurol.2009.282
Publisher site
See Article on Publisher Site

Abstract

In reply Dr Iorio and colleagues describe the results of a retrospective analysis that examined the relationship between exclusive breastfeeding and postpartum relapses in 23 women followed up at their center. Their results are remarkably similar to those we described1 and actually support, rather than contradict, our overall conclusions. They found that women in the NBF group were twice as likely to relapse in the postpartum year and did so sooner than women in the BF group (proportions of women with relapses in NBF and BF groups, 53% vs 25%, respectively). Their results failed to achieve statistical significance, but this is simply owing to low study power. The belief that failure to achieve statistical significance is proof of no effect is a well-recognized statistical fallacy.2 Hellwig et al also confirm our results. Based on a predominantly retrospective analysis of 156 women, they found a statistically significant 2.3-fold higher rate of relapse in those who do not breastfeed exclusively during the first 3 months after birth. Taken together, both articles support our findings and demonstrate the importance of distinguishing between exclusive and nonexclusive breastfeeding. While the magnitude of the effects reported by Iorio et al and Hellwig et al are large, they are smaller than the effect size we observed in our study. This difference is most likely owing to imprecision in how both groups measured exclusive breastfeeding and postpartum relapses. It is well known that relying on retrospective review of routine medical records to assess MS relapses results in underestimation of the true relapse rate; indeed, the number of postpartum relapses that Iorio et al observed is substantially fewer than what we1 and others3 have observed through protocol-driven prospective assessments. Retrospective assessment of exclusive breastfeeding is also subject to significant measurement error, likely because of societal pressure to breastfeed. In our prospective study, we found that some women who report regular use of formula during the first 2 months after birth later reported (1 year after birth) that they did not start formula until more than 2 months after birth. Both of these types of measurement error would reduce the size of the observed effect. Despite these methodological shortcomings, both groups were able to detect a clinically significant difference between women who breastfed exclusively and those who did not, though the small study by Iorio et al did not reach statistical significance. Thus, both data sets support the overall conclusions of our study and indicate that the true effect of exclusive breastfeeding is likely to be quite large. Future studies to confirm or refute this protective effect of exclusive breastfeeding should use rigorous, prospective methods to measure exclusive breastfeeding and postpartum relapse. Correspondence: Dr Langer-Gould, Departments of Research and Evaluation and Neurology, Kaiser Permanente Southern California, 100 S Los Robles, Fourth Floor, Pasadena, CA 91101 (annette.m.langer-gould@kp.org). Financial Disclosure: None reported. References 1. Langer-Gould AHuang SMGupta R et al. Exclusive breastfeeding and the risk of postpartum relapses in women with multiple sclerosis [published online ahead of print June 8, 2009]. Arch Neurol 2009;66 (8) 958- 963PubMedGoogle ScholarCrossref 2. Cox DR Statistical significance tests. Br J Clin Pharmacol 1982;14 (3) 325- 331PubMedGoogle ScholarCrossref 3. Confavreux CHutchinson MHours MMCortinovis-Tourniaire PMoreau TPregnancy in Multiple Sclerosis Group, Rate of pregnancy-related relapse in multiple sclerosis. N Engl J Med 1998;339 (5) 285- 291PubMedGoogle ScholarCrossref

Journal

Archives of NeurologyAmerican Medical Association

Published: Dec 1, 2009

Keywords: breast feeding,mothers,multiple sclerosis,postpartum period

References