ROANOKE TIMES
Copyright (c) 1995, Roanoke Times
DATE: Thursday, December 7, 1995 TAG: 9512070081
SECTION: NATIONAL/INTERNATIONAL PAGE: A-1 EDITION: METRO
DATELINE: BOSTON
SOURCE: DANIEL Q. HANEY ASSOCIATED PRESS
THE BEST NEWS for couples trying to conceive: Try more often.
A myth-quashing new study pinpoints nature's window of fertility: There are six days in every menstrual month when a woman can get pregnant.
The findings have implications for couples striving to have children, as well as for those who want to avoid pregnancy.
Still, it offers no sure-fire formula for people who want children.
``The trick to all this is for couples to know their fertile days,'' said Dr. Allen J. Wilcox. ``There is no good way to do that.''
Perhaps the best advice is: Have sex often.
Until now, estimates of women's fertility ranged from two days in a menstrual cycle to 10 or more.
But the study found that conception is possible if a woman has intercourse on the five days before ovulation as well as on the day her ovaries release a new egg.
Sex before that six-day period almost certainly will not result in pregnancy. And, to the researchers' great surprise, intercourse just one day after ovulation won't, either.
The often-repeated idea that couples should save up and have intercourse on the day closest to ovulation turns out to be false.
On the contrary, the study ``suggests that you increase your chance of pregnancy with increased frequency of intercourse,'' said Wilcox, its lead author.
Ideally, a couple would want to know five days in advance when ovulation will occur and have sex on those days. Test kits now on the market will reveal when ovulation is occurring, but by then it's almost too late.
However, couples can keep track of ovulation over several months to help estimate when it will occur. This way, they can guess when their fertile six days will start.
Moreover, test kit information is useful for those who want to prevent pregnancy without using other forms of birth control. Once the test shows ovulation has occurred, sex is unlikely to result in pregnancy, although they need to resume abstinence when the six fertile days roll around again.
``One reasonable caution is to say there may be a very small probability of conception on the day before and the day after that six-day window,'' Wilcox said. ``We can't rule that out. If you are trying to avoid pregnancy, you might reasonably want to add a buffer onto both sides of that window.''
And timing clearly is not everything.
``Even couples who are very fertile are not fertile in every cycle,'' Wilcox said. ``We don't understand why that is.''
Wilcox and colleagues from the National Institute of Environmental Health Sciences in Research Triangle Park, N.C., publish their findings in today's issue of the New England Journal of Medicine.
Wilcox, who also teaches at the University of North Carolina, based his findings on 221 women who wanted to get pregnant. All of them stopped using birth control, collected daily urine specimens and kept records of when they had intercourse.
From this, the researchers could calculate when the women ovulated and when they got pregnant.
The probability of conception ranges from 10 percent when intercourse occurs five days before ovulation to 33 percent when it happens on the day of ovulation itself. Daily intercourse results in the highest chance of pregnancy - 37 percent.
However, about one-third of all pregnancies end in miscarriage, so the probability of actually having a baby is lower. In a typical month, the researchers figure, there is a 10 percent chance of a successful pregnancy if couples have intercourse once a week. With sex every other day, it is 22 percent. With daily intercourse, it is 25 percent.
Among other findings of the study:
Contrary to another common belief, there is no evidence that the timing of intercourse influences whether the baby will be a boy or a girl.
Sperm has a fairly short shelf life. Ninety-four percent of pregnancies result from sperm that has lingered less than three days. There were no pregnancies from sperm more than five days old.
There is also no sign that aging sperm is more likely to produce babies with defects, although the study was too small to prove this conclusively.
In an editorial in the journal, Dr. Joe Leigh Simpson of Baylor College of Medicine in Houston noted that Wilcox and colleagues delved into a field ``traditionally characterized by much witchcraft.''
``The current report contains information of considerable interest to medical scientists and cocktail party-goers alike,'' he wrote.
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