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Sizing up the risk of pregnancy.

Sizing up the rist of pregnancy

When the FDA approved an implantable, five-year contraceptive in December, the device became one of the most effective birth control methods on the market. However, the method appears less reliable in some women than in others. A new research report aims to help clinicians identify individuals who may be vulnerable to unplanned pregnancies.

Norplant is the trade name for a set of six thin, rubber-like capsules filled with levonorgestrel, a synthetic hormone. Implanted under the skin of the upper arm, the capsules release levonorgestrel for about five years. The method works by suppressing the monthly release of an egg. In addition, levonorgestrel thickens the cervical lining, helping to keep sperm from reaching an egg. In most women, menstrual cycles become irregular soon after Norplant implantation.

A study described in the February OBSTETRICS & GYNECOLOGY reveals that regular menstrual cycles resume after the first year in up to 60 percent of women who use the device, and that women with regular cycles run a higher risk of unplanned pregnancy than those who remain irregular. For five years, a team led by Donna Shoupe and Daniel R. Mishell at the University of Southern California School of Medicine in Los Angeles studied 234 women with the implants, 10 of whom became pregnant in the course of the study. The researchers noted that eight of those 110 had regular menstrual cycles during the six months before they became pregnant. The data revealed that women with regular cycles had a five-year pregnancy rate of 17.4 percent -- significantly higher than the 4.4 percent rate of women with irregular cycles.

"The reason that implant users with regular bleeding cycles are at greatest risk for pregnancy is that they have a greater frequency of ovulatory cycles than do women with irregular bleeding patterns," the researchers write their report. They advise physicians to suspect pregnancy when a Norplant user with regular cycles misses a period.

Norplant still provides "acceptable" protection from pregnancy for women who experience regular cycles, comments Rosemarie B. Thau of the Population Council in New York City. In general, she maintains, the implants provide a very effective pregnancy shield, in many cases proving more reliable than other methods, including oral contraceptives.
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Title Annotation:effectiveness of Norplant, an implantable contraceptive
Publication:Science News
Article Type:Product/Service Evaluation
Date:Mar 2, 1991
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