Study Reveals Limits of Pregnancy Testing

The researchers say this suggests that perhaps an even larger percentage of pregnancies are undetected by home test kits because of practical limitations and user error. The study was published in the October 10, 2001, issue of The Journal of the American Medical Association (JAMA).

Pregnancy cannot be detected before implantation. The study, which involved 221 women, found that pregnancy tests may not be accurate on the first day or so after a missed period because implantation had not yet occurred. Attachment occurs roughly nine days after fertilization but can range from six to 12 days because of the natural variability in ovulation. The researchers found that 10% of the embryo attachments—and hence new pregnancies—had not occurred by the day the women expected their periods to begin.

"These findings mean that if women were to buy a test kit, follow the directions, and test themselves on the first day of their expected periods, the test would be negative for many women, and they would not know that they'd become pregnant,” said Dr. Allen J. Wilcox, faculty member at the University of North Carolina at Chapel Hill (USA; www.unc.edu) and senior investigator of the study. "This is true even if their doctors had given them a blood test for pregnancy that day.”





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