This excerpt from The Cycle was written by Jennifer Aldoretta
Using the sympto-thermal method of fertility awareness (STM) to achieve a pregnancy, in theory, is simply the opposite of using it for pregnancy prevention. If you know when you’re in your fertile window and you want to avoid a pregnancy, all you have to do is avoid sex; if you want to get pregnant, you simply have to have sex during your fertile window, right? Well, yes and no. Though there is about an 85% chance that a couple will get pregnant over the course of a year when using no method of contraception, there are days during the fertile window when sex is more likely to result in a pregnancy. Namely, any day during the fertile window when cervical fluid is clear, very stretchy, or slippery will be extremely fertile. If spotting is present, even better! The trick is to try to time intercourse as close to the day of ovulation as possible, which can feel like somewhat of a guessing game. However, if you compare the stress of using STM to the stress of having no knowledge of STM and trying to time sex based on an “average” menstrual cycle, it’s far less of a shot in the dark. One must also take into account that a man’s sperm count will not be as high if he ejaculated the previous day. So for pregnancy achievement, timing sex for days when cervical fluid has the highest water content will result in the greatest chances of conception.
Not only is STM great at taking much the guesswork out of becoming pregnant, it also essentially replaces the need to take a pregnancy test! Before I explain why, let’s talk biology (not too much, though). As we know by now, the corpus luteum secretes progesterone during the luteal phase to thicken and maintain the uterine lining. If the egg is, in fact, fertilized and implants into the uterus, it will secrete a hormone called human chorionic gonadotropin, or hCG. This hCG tells the corpus luteum not to break down, as it typically would right before menstruation. So, rather than stopping progesterone production, the corpus luteum is given somewhat of a second wind, and continues progesterone production to maintain the uterine lining needed by the developing embryo. Since progesterone is the hormone responsible for the rise in BBT directly after ovulation, this continued production thanks to the implanted embryo causes BBT to stay high. So by measuring BBT, it’s easy to detect when you’re very likely pregnant. If your BBT stays high for at least 18 consecutive days after the initial temperature shift, it is fairly safe to assume that you are pregnant .
A couple sample pregnancy charts are shown below.
This person experienced a slow-rise temperature shift on cycle day nine. After 18 days of a consecutively high BBT, they can safely assume that they are pregnant. A triphasic pattern—or a BBT that increases a second time, as seen starting on cycle day 20—is often typical of someone who is, in fact, pregnant.
This person experienced a sudden temperature shift on cycle day 18. On cycle day 23, the temperature fell to the coverline, which can happen from time to time during the luteal phase. This individual also experienced a triphasic pattern, since their BBT rose for a second time on cycle day 32. After 18 days of an elevated temperature, they can safely assume that they are pregnant.
Unfortunately, a pregnancy resulting in a miscarriage is sometimes a fact of life. It’s never an easy situation to encounter, especially when that pregnancy is wanted. Although I so hope that anyone reading this book never suffers through such an event, it is good to understand the warning signs. If a pregnancy has been confirmed (or indirectly confirmed by 18 days of an elevated post-ovulatory BBT) and BBT begins to fall after that point, it may be an indication of an impending miscarriage . See the sample chart on the next page.
After 18 days of a sustained temperature rise, this person's BBT begins to fall significantly starting on cycle day 31. Unfortunately, this person experiences an early-stage miscarriage after a confirmed pregnancy.
I would also recommend reading about using the sympto-thermal method to maintain or improve reproductive health for information on reproductive disorders that can lead to difficulty getting pregnant or carrying a pregnancy to term.