When Is a Woman Most Fertile?
Fertility means the ability to conceive and have children. The word “fertile” is also often meant to mean that a woman has the ability to become pregnant through normal sexual activity — fertility treatments may make it temporarily possible for a woman to become pregnant without being literally “fertile.” The opposite of fertility, infertility, is defined by a failure to conceive after a year of regular intercourse without contraception.
So when is a woman most fertile?
Fertility in the Average Menstrual Cycle
In a perfect world, an average menstrual cycle is 28 days. That means that from the first day of a woman’s menstrual bleeding, there will be twenty-eight days until her next period starts. This means that “day one” a woman’s cycle is her first day of bleeding, and day 28 is the earliest possible date for her period to return.
So why do periods happen? The menstrual period happens because a woman’s reproductive cell, or egg, does not get fertilized. Eggs are fertilized by sperm, so women who don’t have intercourse during their 28 day cycle won’t become pregnant. Other means exist to prevent pregnancy as well, and if birth control is used, the likelihood that an egg becomes fertilized is greatly reduced. Menstrual periods happen about 12 to 14 days after the egg is produced.
If you do a little math, that means that for an “average 28 day cycle” the egg is available for fertilization by day 14, or two weeks to the day after the start of the menstrual period. Sperm lives happily for up to 48 hours in the vagina or on the uterine wall, so you have to add a couple of days of possible pregnancy to that number. All this adds up to equal an “ideal fertility time” of between 12 and 16 days after the start of a woman’s period.
Pretty complex answer, right? Fertility is a complicated thing, relying on the woman’s body to be in sync, and requiring that a male’s sexual reproductive cells are working properly too.
Using Fertility to Your Advantage
What does this mean? Around two weeks after the start of your period is your fertility window. If you are trying to avoid have children, you should especially avoid sexual intercourse during this window, and always use proper birth control. Remember, sperm can live in the vagina for a while so it is especially important to use condoms.
If, on the other hand, you are attempting to become pregnant, this period is of great importance to you. Though it is possible to become pregnant at any point in a woman’s menstrual cycle, the odds vary greatly depending on the time of the month. If you are hoping to have a baby, have plenty of unprotected intercourse between the twelfth and sixteenth day of your cycle. That’s all there is to it.
When Is a Woman Least Fertile?
Since we know the days when women are most likely to become pregnant, we should be able to figure out the days in which she is least likely to reproduce.
Since the egg is produced about fourteen days after the start of a woman’s period, and since sperm have a way of sticking around for a few days, we know that a woman’s least fertile period has to be within the first ten days or so. We can narrow it down even more — scientists tell us that woman’s least fertile period is in the first seven days of her menstrual cycle. Yes, that means that a woman’s least fertile point is during her period, but that doesn’t mean that becoming pregnant during a period is unheard of — it just means that the odds are really stacked against pregnancy at this point.
The first seven days of a woman’s cycle are the least hospitable for sperm, for many reasons. The most obvious is the period itself — for a woman to ovulate while she’s on her period is a rare occasion indeed, but that doesn’t mean it won’t happen. Other reasons for infertility during menstruation — the vagina is less receptive to sperm.
Remember that, though the deck is stacked against fertility, it is still possible for a woman to become pregnant while she is on her period.
What About Longer or Shorter Menstrual Cycles?
If a woman’s cycle is different from the “28 days” often called “average”, her fertility period will be a little bit different. It is easy to figure out your most fertile time on your own if you remember that ovulation tends to occur about two weeks after the start of your period.
Most women’s cycles are between 24 and 34 days long. By the numbers, most women’s menstrual cycle is between three and five weeks long — for women who have longer or shorter menstrual cycles, determining their most fertile time seems complicated.
If you have a longer menstrual cycle, you will naturally ovulate less often than women with shorter cycles. We’re not talking about a huge missed opportunity here — women with a 34 day cycle, for instance, have two fewer fertile periods per year than women with a 28 day cycle. On the other end of the spectrum are women with short menstrual cycles. If your cycle is 21 days long (very short but not unheard of), you will actually have as many as two or three more ovulation opportunities than women with an “average” menstrual cycle.
If you’re attempting to avoid pregnancy and you have a longer cycle, your least fertile period is still the first seven days of your cycle. Your most fertile period is still 12 to 16 days after the start of your cycle. The big difference is that you have a longer period after ovulation in which you may become pregnant, so be extra careful after the first week of your menstrual cycle.
The menstrual cycle and fertility period seem pretty complicated. To further complicate things, every woman’s body is different. Some women ovulate with more frequency, some have extremely light periods and short cycles — the ability for a woman to become pregnant depends partly on the time of the month and partly on her body chemistry.