What does “trying to get pregnant” mean? Ovulation prediction kits that are available at every drugstore, smartphone apps, and websites are available to try to predict that six-day (on average) time when sperm and egg have a chance at uniting.
However, lots of people who say they are trying to conceive are not doing anything in particular, except throwing the birth control out and probably having sex more often than usual. (How often is that you ask? Check out our previous post on that subject.). For example, in one cohort study of Danish women, less than half of women aged 35-40 were using a method to improve their odds of timing intercourse to maximize their chance of conception, such as charting their basal body temperature, monitoring cervical mucus, or using a luteinizing hormone or ovulation test kit. A smaller US-based study of women trying to conceive found that only 6% of women checked their cervical mucus consistently, but those that did were twice as likely to get pregnant.
Other research also suggests that couples often have trouble identifying when the fertile window occurs. One study—albeit one funded by a fertility monitor manufacturer—found that most women who started using a fertility monitor became pregnant within three cycles. Based on this, the authors concluded that most of the couples had been previously mistiming intercourse, even though 84% said they had used some method of predicting ovulation. Dr. Allen J. Wilcox, one of the epidemiologists to identify the six-day fertile window in the 1990s pointed out this problem, noting that couples may easily miss the window by trying to time intercourse precisely. Anecdotally, we have heard this in conversation with friends, and two women interviewed for our book described using methods to predict ovulation incorrectly for a while, before they figured out their error.
We are also exposed to misleading conventional advice. In a subsequent study, Wilcox wrote, “In only about 30% of women is the fertile window entirely within the days of the menstrual cycle identified by clinical guidelines—that is, between days 10 and 17. Most women reach their fertile window earlier and others much later.” (In order words, the rhythm method does not work for birth control – but you already knew that, right?)
In his 2010 book, Wilcox describes “How Can Women Identify Their Fertile Days?” as one of the unanswered questions in reproductive epidemiology. The problem is that once the signs impending ovulation are noticeable, most days in the six-day fertile window have passed. The conventional wisdom is that if your cycle is regular, then most likely your fertile days are the same for every cycle and that is the potential benefit of basal body temperature charting. However, Wilcox argues against putting too much faith in this notion.
On the other hand, in a 2004 study, Wilcox examined a group of women who were not trying to conceive and found that they were more likely to have intercourse during their fertile window. The study was unable to explain why—it could be an increase in female libido, a male response to female pheromones, or even that intercourse influences the timing of ovulation. So maybe trying by not trying too hard is a valid strategy. One of our friends, trying to conceive at age 39, was advised by her doctor to make love every other day, rather than trying to predict the most fertile times. (It worked! She had a healthy baby within a year.)
If this post is starting to seem a bit self-contradictory, here is the message in bullet points: