Using a calendar to determine fertility could backfire
A couple employing the “rhythm” method of contraception can result in a baby more often than expected, data shows. Study suggests that partners who rely on the rhythm or “calendar” method, one of the biological forms of birth control, to determine fertility could end up hearing the pitter patter of little feet sooner than expected--or wanted.
The rhythm method for getting pregnant--or avoiding it--assumes a woman is fertile between Day 10 and Day 17 of her menstrual cycle.
But the new study, which examined women mostly between ages 25 and 35, when the menstrual cycle is the most regular, suggests only 30 percent of women fit this category.
Others could be fertile almost any day, says obstetrician/gynecologist David Harari, MD, of Scripps Mercy Hospital in San Diego. “Some women ovulate and are fertile in an earlier time in their cycle, other women may ovulate later in their cycle,” reports Harari. “Patients assume that if they are ‘on their period’ it is OK to have intercourse without any type of contraception, because they are not going to get pregnant: that just isn’t true.”
Researchers at the US National Institute of Environmental Health Sciences, which conducted the study, examined estrogen and progesterone ratios from urine samples taken during 700 menstrual cycles of 213 healthy North Carolina women.
Planned Parenthood statistics show that 25 women out of 100 women get pregnant on the rhythm method during the first year they try it.
There is a normal tendency for teenage women and those approaching menopause to experience less regular cycles. “The ‘safety period’ has been passed down perhaps by tradition, by word of mouth over the generations, and some of that information truly has not been very accurate,” Dr. Harari says. “Not all women have a traditional 28 day cycle to begin with.”
For them, fertility is less predictable.
The federally funded study indicates that those women are potentially fertile on almost any day, even the day menstruation begins. Seventeen percent of study participants were found to be starting their fertile window by Day 7 (with cycle Day 1 being the time when menstrual bleeding begins).
“The second largest unwanted pregnancy category is women 40 and older and one of the reasons for that is not that they are uneducated or they don’t know how to use contraception, but because there is a lot of variability in their cycle,” says Harari. “It’s very difficult for them to know exactly when they are fertile.”
Dr. Harari, who regularly sees patients who are shocked at the positive outcome of their pregnancy test, say conventional contraceptives and condoms provide better success rates than the rhythm method, which he doesn’t consider to be a form of birth control.
Husband and wife Don and Dorene Schloeder, who have four kids, know Dorene is now having irregular fertility cycles. “I’ve had some cycles where I’ve probably ovulated Day 4 or 5 and then others where it’s Day 25,” reports Dorene. “We conceived on my 5th or 6th day of my cycle.”
The Schloeders are educators of natural family planning, an approach using various modern methods to achieve or avoid pregnancy without drugs or artificial devices. Explains Dorene, “Most of my life I have been pretty regular, but more recently it’s been irregular. It’s why we used [natural] family planning because we can tell when we are going to ovulate, I can tell by the observation I am making.”
Dorene checks her temperature in the morning and makes observations of cervical mucus secretions. “If we happen to be in the mood when I’m fertile, then we take advantage,” she adds. It took some time, about a year, to conceive their daughter Elizabeth, their fourth child.
Allen J. Wilcox, MD, PhD, chief of epidemiology at NIEHS, concludes that if a healthy couple wants to get pregnant they should throw out “fertile window” planning. “Simply engage in unprotected intercourse two or three times a week,” he says.
The NIEHS report, published in the British Medical Journal, indicates that “data suggest there are few days of the menstrual cycle during which some women are not potentially capable of becoming pregnant--including even the day on which they may expect their next menses to begin.”
Dr. Harari generally recommends ovulation kits to track fertility. He says vaginal infections and other complications can make observation alone less reliable than simple at-home tests.
From the beginning of his and his wife’s partnership, The Schloeders believed that predicting fertility by the calendar alone was too much of a gamble. Says Don, “We would probably have had one or two more children than we have today, if we had gone strictly by rhythm.”
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