Most of us spend the better part of our fertile years actively trying not to get pregnant, so it's always an unpleasant surprise to learn that it's not actually that easy to conceive. The reality is there is a relatively short window during a woman's cycle that she can get pregnant whether or not she's on birth control or actively trying.
In fact, there's really only a 48-hour period that is ideal for conceiving, according to Anate Brauer, M.D., a reproductive endocrinologist at the Greenwich Fertility and IVF Centers and assistant professor of OB/GYN at NYU School of Medicine. Of course, every woman is different, as are her monthly cycles, so it's never a sure bet to say that there's any week or day when you absolutely cannot get pregnant (so always use protection if you're not trying to conceive).
If you're wondering which occasions make for the least likely opportunity to conceive, however, here are some expert-stamped scenarios where your chances are low.
If you're on birth control, be it the pill, patch, ring, implant, IUD, or the shot (Depo-Provera), and you're following all instructions, your chances of getting pregnant are less than 1 percent. "Hormonal contraception works by preventing the recruitment of a mature egg," explains Dr. Brauer. Even if you're committed to taking your birth control, you still have to be careful, since traditional pill packs typically contain 4-7 days of sugar pills that do not contain hormones, and, in some women, 4-7 days without exposure to hormones may be long enough to allow for recruitment of a mature egg. "This is often referred to as 'escape ovulation' and is one reason for oral hormonal contraception failure," says Dr. Brauer.
While it's not totally impossible to get pregnant while Aunt Flo is in town, your chances are pretty darn slim. If you consider what's actually happening inside your body while you're on your period, you can understand it a bit better: The egg that was growing inside your ovaries and waiting to be fertilized wasn't and, as a result, your uterine lining sheds (this is the "blood" that's released) and prepares to grow new follicles (aka eggs) for your next cycle. In other words, the egg that was viable for fertilization has now been flushed along with your period. The exception, however, is if you have particularly short cycles. "Sperm can live in the uterus for up to five days, so if you have intercourse towards the end of your period, sperm can still hang around long enough to fertilize an egg that is released days after your period ends," explains Dr. Brauer.
This old-school method of preventing pregnancy is a far cry from a myth. No, it's not foolproof and it can certainly result in pregnancy, but it does significantly decrease your chances of getting pregnant. In case you need a refresher course on the pull-out method, it involves the male partner pulling out of the vagina before he ejaculates. The problem, however, is that pre-ejaculate, or precum, the bodily fluid that's released from the penis before an actual ejaculation, very well may contain active and viable sperm. Additionally, Mark Trolice, M.D., reproductive endocrinology and infertility specialist at My Fertility CARE: The IVF Center in Winter Park, Florida, explains that most men aren't aware of when they release this precum. "Because it's hard to predict when pre-ejaculation occurs, the withdrawal method is often fraught with peril and certainly not the most reliable method out there," he says.
Your chance of getting pregnant with condom use is about 15 percent, and that's accounting for human error. With perfect condom use every single time, those odds decrease to 2 percent, according to Planned Parenthood. Correct usage means the condom is rolled onto the male partner's penis before there's any contact between genitals and skin (see the above note on the potential potency of pre-cum). There are ways to make rubbers even more effective, though: Pair them with another form of birth control, like an IUD or the pill, or use them in combination with the pull-out method.
If you haven't had a period after giving birth, especially if you're breastfeeding, it's actually unlikely that you can become pregnant. "While breastfeeding, the hormone, estrogen, which is responsible for getting your period each month, is suppressed," explains Sherry Ross, M.D., OB/GYN, Women’s Health Expert in Santa Monica, and author of She-ology. "Additionally, the hormone that stimulates breast milk production, prolactin, also prevents ovulation from occurring because it inhibits the FSH hormone that triggers your ovaries to grow and release eggs." Bottom line: Without a period, you will not ovulate regularly so it is less likely, though certainly not impossible (ever heard of Irish twins?), that you can become pregnant.
Thanks to that good-old biological clock that has hardly changed its tickers since the dawn of time, women's chances of getting pregnant wane over time. While we're born with some 1-2 million eggs, there's only about 300,000 left by the time we get our first period and only about 25,000 by the time we're in our late 30s. This means that a woman's chances of becoming pregnant in her early 40s are pretty slim, though it's by no means impossible. According to Dr. Ross, women over the age of 44 have a less than 5 percent chance of getting pregnant each month. "As we get closer to 40, the ticking of our biological clock becomes louder and by 44, it can be deafening," she says. "Fertility decreases by as much as 95 percent in women between 40 and 45 years of age."