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Prenatal testing for Down syndrome is currently recommended for women 35 years of age and older (or women whose blood or ultrasound tests suggest their risk of having such a baby are greater than that of an unscreened 35-year-old). This threshold was chosen because 35 is the age at which the risk of miscarriage due to these diagnostic procedures (about 0.5 percent) is equal to that of having a baby affected by Down syndrome.
This recommendation presumes that women regard these outcomes equally. But this is not the case, according to a recent study by researchers at the University of California, San Francisco Medical Effectiveness Research Center for Diverse Populations. The center is led by A. Eugene Washington, M.D., M.Sc., and supported in part by the Agency for Healthcare Research and Quality (HS07373).
The researchers found that on average, regardless of racial, ethnic, or educational background, women felt that having a child with Down syndrome would be worse than having a miscarriage due to amniocentesis or other prenatal diagnostic procedure. Only the subgroup of women who were eligible for but chose to forego prenatal diagnosis viewed both prospects as equally burdensome.
This variation in individual preferences calls into question the basis for prenatal testing guidelines. Current guidelines do not consider individual preferences in lower risk women, but they should, concludes the study's first author Miriam Kuppermann, Ph.D., M.P.H.
Dr. Kuppermann and her colleagues assessed responses to interviews and survey questions for 539 sociodemographically diverse pregnant women who sought obstetric care at various practices in the San Francisco Bay area. The women were asked about the prospects of procedure-related miscarriage versus a Down syndrome-affected birth.
The researchers used time trade-off and standard gamble techniques for quantifying preferences for health outcomes and calculated the difference in preference scores for the two outcomes. On average, procedure-related miscarriage was preferable to Down-syndrome, as indicated by positive differences in preference scores that were significantly greater than zero: a mean 0.09 time trade-off difference and a mean 0.11 standard gamble difference. However, individual preferences for these outcomes varied profoundly and correlated strongly with attitudes about miscarriage, Down syndrome, and diagnostic testing.
More details are in "Procedure-related miscarriages and Down-syndrome-affected births: Implications for prenatal testing based on women's preferences," by Dr. Kuppermann, Robert F. Nease, Jr., Ph.D., Lee A. Learman, M.D., Ph.D., and others, in the October 2000 Obstetrics & Gynecology 96(4), pp. 511-516.
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