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Samuel Shapiro, MB; Allen A. Mitchell, MD
Martha M. Werler, ScD Boston (Mass) University School of Medicine

JAMA. 1990;263(20):2748.

	Since this article does not have an abstract, we have provided the first 150 words of the full text PDF and any section headings.

To the Editor.—

In their discussion of the apparent protective effect of multivitamin/folic acid supplements on the risk of neural tube defects (NTDs), Milunsky et al¹ claim that "the timing of the interviews in early pregnancy and the fact that the vast majority of mothers were unaware of pregnancy outcome minimized the possibility that this finding was due to their selective participation or biased recall of supplementation."

With regard to selective participation, all women were recruited from those whose -fetoprotein or amniocentesis samples were submitted to the authors or their colleagues. However, unless all samples (or a random sample) from each participating center were included, the possibility of selection bias cannot be excluded. Such a bias becomes a strong possibility for the 19% of amniocentesis samples analyzed elsewhere, since those women may have been referred preferentially when their samples yielded a diagnosis of NTD and there was no history . . . [Full Text PDF of this Article]

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