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Harvard Commentaries
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Harvard Commentaries
Reviewed by the Faculty of Harvard Medical School


Medical Myths Medical Myths
 

Advice You Can Safely Ignore About Getting Pregnant


October 23, 2012

By Robert H. Shmerling M.D.

Beth Israel Deaconess Medical Center


If you're thinking of starting a family, get ready for lots of advice. And get ready to hear some partially true or flat out wrong information. Some of it is predictable — it's been around for years, perhaps centuries. While the list of common, unhelpful advice is long, here are some of the more common bits of "wisdom" related to getting pregnant that you can safely ignore.

Getting Pregnant? Don’t Listen To This!

1. You’ll be pregnant within a few months of trying.

In fact, 80% to 85% of women become pregnant within one year of trying, 90% to 95% are pregnant within two years, and the remaining 5% to 10% are considered to have fertility problems. Estimates for chances of getting pregnant are 20% to 30% per menstrual cycle. The chances will vary depending on a number of factors (including age, current and past medical problems, certain medication use, timing of intercourse, and the fertility of one's partner) but many healthy, fertile couples are not pregnant even after six months. It is common that couples only need to wait a bit longer and learn more about the best time to have intercourse (based on the woman's menstrual cycle, or ovulation pattern). Referral to an infertility specialist is generally reserved for couples who have been unsuccessful after trying for a year, although for women 35 years of age or older, referral may be recommended after a shorter amount of time.

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2. You cannot get pregnant if you have sex while you have your period. And: During each menstrual cycle, there is only one day in which a woman can get pregnant.

There is virtually no way to categorically identify a time when it’s impossible to become pregnant after having sexual intercourse. If sex happens, pregnancy may follow. However, there are clearly times of the month when fertility is much higher and other times when it is quite low. Here's the important biology to know:

    • An egg is released from the ovary during ovulation and can be fertilized for about 12 to 24 hours after its release — presumably, that's where the "one day" fertility myth comes from. However, sometimes more than one egg is released, so that an egg may be "available" for up to two days. In addition, sperm can last up to five days in the cervix, uterus and fallopian tubes. It takes sperm a couple of days to make the trip to the fallopian tubes to meet the egg, so, you increase your chances of getting pregnant by having sex during the one week period that starts five days before ovulation and ending two days after ovulation. The trick is knowing when ovulation will occur (see below).
    • Ovulation occurs 14 days before the beginning of your next period, not, as many people believe, 14 days after your last one. (The one exception is if you happen to have a regular cycle of 28 days, in which case you ovulate 14 days before and 14 days after your last period.) The big problem is this: Trying to time sex to an event that’s going to happen in the future is quite difficult and not terribly accurate. Unless your cycles are highly regular, you may not know when that is. For example, if you have regular, 30-day cycles, you should ovulate on day 16, counting from the beginning of your last period; but if your cycles vary in length, it will be impossible to guess without help. That help could come in the form of kits that measure hormones or body-temperature monitors that can help you predict when you will ovulate.
    • Because menstrual cycles and ovulation dates tend to vary for a given person, timing sex to avoid pregnancy (rather than to seek pregnancy) is also not terribly effective.

 

    • If you have sex toward the end of your period and you happen to ovulate early in your cycle, it is certainly possible to get pregnant, even after having sex during your period.

Remember that the “rhythm method” was a way to improve the chances of getting pregnant, not to avoid pregnancy. Stated another way, given the nature of human biology, it is easier to increase your odds of getting pregnant by having sex at an particularly favorable time than it is to avoid pregnancy by having sex at a particularly unfavorable time.

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3. The chances of getting pregnant are greatly affected by the couple’s position during or after intercourse.

There is a certain intuitiveness about the effects of position on the chances of pregnancy. Gravity is perhaps the most obvious reason one might expect position to matter: Sperm must swim through the cervical opening, into the uterus, up the fallopian tubes to where the egg is. All of this effort might seem easier if the sperm did not have to swim "uphill," but the fact is, sperm can be found in the uterus 20 minutes after intercourse regardless of the position of the partners during or after sex, and there are millions of sperm involved in the effort. Thus, as appealing as the suggestions may be, there is little evidence that assuming a particular position during or after intercourse will dramatically affect fertility. Lying still (versus moving around) or lying on your stomach will not reliably increase fertility. And, clearly, these are not reliable ways to avoid pregnancy.

 

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4. The chances of getting pregnant are greatly affected by the type of underwear the man wears.

This myth is derived from the knowledge that sperm are stored in the testicles which, in turn, reside in the scrotum. This location outside the body cavity is much cooler than the rest of the body; when body temperature is elevated or when men wear tight-fitting clothing that keeps the testicles nearer to the body, sperm counts and sperm activity may be reduced. That’s why men with low sperm counts or other fertility problems are advised to avoid hot baths or tight-fitting clothing that might elevate the temperature of the sperm. However, for the vast majority of healthy men, fertility is not appreciably affected by what they wear or how they take their baths. Men with normal fertility cannot reliably increase it by changing from briefs to boxers; nor should men rely on their choice of undergarments to avoid parenthood.

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5. A woman's fertility plummets after age 35.

The effect of age on fertility is gradual, without a specific age of onset. In fact, a reduction in fertility can be detected as early as age 27 and it declines each year thereafter; by the time you are 35, it declines by an estimated 3 percent per year; for each ovulation, the chances of pregnancy are about half what they were at age 25. And, young women can have fertility problems, especially if there are risk factors such as prior sexually transmitted disease, chronic medical problems or certain gynecological surgeries in the past.

6. If you’re having trouble getting pregnant, there’s probably a problem with the woman’s anatomy.

When a fertility problem can be identified, estimates vary regarding how often it is related to male, female or a combination of factors. However, the man is responsible for at least part of the difficulty conceiving in up to 60% of cases (being solely responsible in 20% to 30% and contributing to a combined problem in another 20% to 30%). A problem solely with the female partner is said to account for about 35% to 40% of infertility cases and some small proportion cannot be traced to either partner.

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Why All The Myth?

Perhaps it’s because reproduction seems so mysterious in the first place that so much myth has built up around it; on the other hand, getting pregnant is fairly straightforward most of the time. Knowing a few of the basic biology facts regarding timing and proximity of sperm and egg are usually all that is necessary. For those who have difficulty conceiving, of course, it’s not simple at all — proof that what most couples take for granted is actually a remarkably complicated system. And there is a lot that we still do not understand.

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The Bottom Line

If you are planning to start a family, congratulations and good luck! Do what you can to increase the chances of getting pregnant and having a healthy baby. But while it’s important to think ahead and look for advice from reliable sources, don’t believe everything you hear. Check out websites with reliable information about pregnancy even before you are pregnant. Or talk to your doctor to find other good sources of information. Talk with your health care professionals about any health concerns you have, past medical problems or medications that may be relevant, and whether there is any reason to wait before trying to conceive.

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Robert H. Shmerling, M.D. is associate physician at Beth Israel Deaconess Medical Center and associate professor at Harvard Medical School. He has been a practicing rheumatologist for over 20 years at Beth Israel Deaconess Medical Center. He is an active teacher in the Internal Medicine Residency Program, serving as the Robinson Firm Chief. He is also a teacher in the Rheumatology Fellowship Program.

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