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Rethinking Reliability of Fertility Cycles


The so-called fertile window during a woman's menstrual cycle is much larger than had previously been believed, according to government researchers.

Guidelines for getting pregnant--or for avoiding pregnancy--generally assume that an average woman is fertile between days 10 and 17 of her menstrual cycle, with the onset of menstruation counting as day one. But new data indicate that only about 30% of women actually have their fertile window entirely within that time span. In fact, researchers found, there is hardly a day within the menstrual cycle during which some women are not potentially fertile.

Dr. Allen J. Wilcox and his colleagues at the National Institute of Environmental Health Sciences studied 696 menstrual cycles in 213 healthy North Carolina women. The women donated urine samples each day so that the team could measure levels of estrogen and progesterone. An abrupt change in the ratio of these two hormones marks the beginning of ovulation.

The team reported in the Nov. 18 British Medical Journal ( that 2% of the women were starting their fertile window by day four, and 17% by day seven. More than 70% were in the fertile window before day 10 or after day 17, leaving few "safe" days for such natural birth-control techniques as the rhythm method.

"If the average healthy couple wants to get pregnant," Wilcox said, "they are just as well off to forget fertile windows and simply engage in unprotected intercourse two or three times a week."

Risky Pregnancies Linked to Timing

In a separate pregnancy-related study, researchers from the Pan American Health Organization in Uruguay found that gaps between pregnancies of fewer than six months or of more than 59 months increase the risk of complications during the second pregnancy. The team studied inter-pregnancy intervals for more than 400,000 women in Latin America and the Caribbean.

They reported in the Nov. 18 British Medical Journal that, compared with women with pregnancy intervals of 18 to 23 months, those with intervals of fewer than six months had a 2.5-fold higher risk of death, a 70% increase in bleeding during the later stages of pregnancy and a 30% increased risk of infection and anemia. Women with intervals longer than 59 months were more likely to develop pre-eclampsia and eclampsia, disorders of high blood pressure during pregnancy.

The authors suggest that the short intervals do not allow the mother's body to recover from the physical stresses imposed by the first pregnancy. Women with long intervals lose the protective effect for pre-eclampsia generally associated with a recent pregnancy.

Heart Assn. Urges More Soy in Diet

The American Heart Assn. last week officially recommended that all Americans add soy to their diets to reduce the risk of heart disease. Several studies have shown that soy reduces cholesterol levels and lowers the risk of heart attacks. One recent study, for example, showed that eating 20 grams of soy per day can reduce cholesterol levels in as few as nine weeks.

Soy milk contains 6 to 8 grams in an 8-ounce serving. Three ounces of tofu has 8 to 10 grams of soy protein and a soy burger has 10 to 18 grams. Now if they could only make it taste good.

Cell Therapy May Help Repair Heart Damage

French researchers have used cell therapy to restore the function of dead heart muscle in a patient severely disabled by a heart attack. Although the study involved only one patient, it suggests that new approaches using stem cells may have a wide application in treating heart disease.

Dr. Philippe Menasche of the Hopital Bichat in Paris said at an American Heart Assn. meeting in New Orleans last week that he and his colleagues had collected muscle cells from the thigh of a 72-year-old heart attack patient, grown them in the laboratory for two weeks, then injected them into a portion of the heart that was badly damaged. Five months later, he said, "there is new contraction and viability in the area that previously was dead."

At the same meeting, Dr. Ray C.J. Chiu and his colleagues at the McGill University Health Centre in Montreal reported that they had used stem cells to produce new heart muscle in 20 of 22 rats. The stem cells were taken form the animals' own bone marrow.

Niacin May Boost Effect of Cholesterol Drugs

The beneficial effects of cholesterol-lowering drugs called statins can be dramatically improved by administering the vitamin niacin with them, according to researchers from the University of Washington in Seattle.

While cholesterol-lowering drugs can reduce the risk of heart attacks by about 35%, a combination of the statins and niacin reduces risk by about 70%, Dr. Greg Brown told the American Heart Assn. meeting. Niacin used alone has been shown in some previous studies to reduce the risk of heart attack by about 20%. The new results suggest that the drugs are synergistic.

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