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Clinical Chemistry 50: 784-785, 2004; 10.1373/clinchem.2004.031120
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(Clinical Chemistry. 2004;50:784-785.)
© 2004 American Association for Clinical Chemistry, Inc.

Letters to the Editor

Unexpected Relationship between Plasma Homocysteine and Intrauterine Growth Restriction: Response

Claire Infante-Rivard1,a and Geroges-Etienne Rivard2

1 Department of Epidemiology, Biostatistics, and Occupational Health, Faculty of Medicine, McGill University, Montréal, Québec, Canada
2 Division of Hematology and Oncology, Department of Pediatrics, CHUME, Hôpital Sainte-Justine, Université de Montréal, Montréal, Canada

aAddress correspondence to this author at: Department of Epidemiology, Biostatistics, and Occupational Health, Faculty of Medicine, McGill University, 1130 Pine Avenue West, Montréal, Province of Québec H3A 1A3, Canada.


To the Editor:

In his letter, Moridani raises a few points about our most recent report (1) on the relationship between maternal and newborn plasma total homocysteine (tHcy) and intrauterine growth restriction (IUGR), and about a previous report showing perinatal references values for tHcy (2). It is not clear to us why, as stated by Moridani, "specimen collection at various points during pregnancy .... [T]o determine whether the difference between the obtained t-Hcy values is meaningful and statistically significant" is more "proper" than what we have done. Our comparison between cases and controls, whose measures of tHcy were taken at the same time, is completely proper and valid. Our conclusions were about perinatal measures of tHcy; if others want to measure and compare tHcy at other times during, or even before, pregnancy, that is another matter. Validity of results has nothing to do with timing of measurements but with quality of measures and appropriateness of the comparisons. Our study meets both.

Another point of Moridani’s letter is confusing to us. It seems to oppose the description of means, or of data, with the notion of "individuals at risk". As a simple descriptive analysis, Table 2 of our report (1) shows mean tHcy values and their confidence intervals. For the comparison of means, elementary statistical theory informs us that confidence intervals that do not overlap are equivalent to a statistically significant difference. As stated in our report, the mean tHcy was different between case and control mothers, but not between case and control newborns. However, the study’s main objective was not to compare tHcy between cases and controls, but to determine whether tHcy is a risk factor for IUGR, accounting for established IUGR risk factors. Moridani seems to have missed this perspective. Our statistical analysis, in which we used unconditional logistic regression and linear regression, which may not be familiar to the author, was completely appropriate for the study’s goal. A box plot is not, to our knowledge, a way to estimate risk, whereas contribution to the probability of disease, i.e., risk, is readily estimated by odds ratios in a multivariable model.

Finally, Moridani proposes an apparently new mechanism for our findings, which relates to a better diet, to be studied along with weight gain during pregnancy. We have already shown in our previous report that a better diet (folate-rich foods) reduces the tHcy concentration (2), and in the present study (1), we measured and adjusted for weight gain during pregnancy. Although Moridani’s suggestion does not seem fruitful, we agree that additional data are required to support the observation of an inverse relationship between tHcy and IUGR, including the roles of vitamin B12 and folic acid.


References

  1. Infante-Rivard C, Rivard GE, Gauthier R, Théoret Y. Unexpected relationship between plasma homocysteine and intrauterine growth restriction. Clin Chem 2003;49:1476-1482.[Abstract/Free Full Text]
  2. Infante-Rivard C, Rivard GE, Yotov W, Théoret Y. Perinatal reference intervals for plasma homocysteine and factors influencing its concentration. Clin Chem 2002;48:1100-1103.[Free Full Text]




This Article
Right arrow Extract Freely available
Right arrow Full Text (PDF)
Right arrow Submit an electronic Letter to
the Editor about this paper
Right arrow Alert me when this article is cited
Right arrow Alert me when eLetters are posted
Right arrow Alert me if a correction is posted
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Similar articles in ISI Web of Science
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow reprints & permissions
Citing Articles
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Infante-Rivard, C.
Right arrow Articles by Rivard, G.-E.
Right arrow Search for Related Content
PubMed
Right arrow Articles by Infante-Rivard, C.
Right arrow Articles by Rivard, G.-E.
Related Collections
Right arrow Pediatric Clinical Chemistry
Right arrow Hemostasis and Thrombosis
Right arrow Endocrinology and Metabolism

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