Home fertility tests may not be reliable predictors of a woman's ability to get pregnant, researchers at UNC-Chapel Hill have found.

The group, led by Dr. Anne Z. Steiner, an assistant professor of obstetrics and gynecology, found that the do-it-yourself kits often indicated women would have difficulties, yet many had no problem conceiving.

"Although the tests are out there, this is the first study that asks, can these tests be used to measure potential fertility?" Steiner said.

Women typically use the tests to gauge their chances of becoming pregnant, particularly if they've postponed child-bearing into their 30s when fertility diminishes. For years, women in the U.S. have delayed their first pregnancies, on average now until age 25; in the 1970s, the average age was 21, according to the Centers for Disease Control and Prevention.

At about age 30, fertility gradually starts to wane as the number and quality of eggs declines. The drop-off is steeper in a woman's late 30s.

Like a pregnancy test, a home fertility detector uses a chemically treated strip that reacts to hormones in the urine and displays a reading. It measures for follicle stimulating hormone, or FSH, a chemical produced in the pituitary gland in the brain that helps stimulate the growth of eggs in the ovaries.

Readings above a certain level are supposed to signal that a woman may be infertile.

But Steiner's group found that abnormal FSH levels did not correlate to reduced fertility among the women who participated in the study.

"When we have larger numbers of women in the study, we will be able to look at how many women conceived in a year despite an abnormal test value," Steiner said.

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