I thought I'd post this, since I have found that many women, even those who are in their fertile years, do not know. Most men don't, though that doesn't surprise me as much.
It very much relates to the topic of contraception inasmuch as the culture (as we have discussed before) treats fertility as an illness to be treated and controlled by medication. But if one understands the natural unmedicated workings of a healthy woman's cycle, by which I mean more than just her monthly cycle, we can learn a great deal about the great care God took when making us reproductive beings.
You will find a TON of contradictory information about these matters. But if you consider the affiliation of the source you will find that the majority of pro-life and non-contraceptive organizations will provide you with the same, or at least very similar information. I learned most of this from my Natural Family Planning(NFP) teacher, Dr. Sears, and the La Leche League International.
First off, as has been discussed in the past, a woman is only fertile for a short period of her monthly cycle. It ranges from 5 to 9 days, depending on the exact time of her ovulation and the quality of her cervical fluid (I could go on and on in order to help explain this, but it is really best if you find a good source for NFP and learn from a trained professional). The fertile period is near the middle of her monthly cycle. The cycle begins on the first day of menstruation. Ovulation does not always occur on the same day after her first day of her cycle, but the same number of days always pass between ovulation until the beginning of her next cycle. This is called a luteal phase. Mine is 15 days. I tend to think that this is pretty cool, but that's just me. ;-)
The statistics that I have been given from my NFP teacher were that a couple not avoiding or attempting to conceive, but having natural relations would conceive on average within 6 months if both partners are healthy. And a couple which is able to observe and follow their fertile patterns when trying to conceive, can after as little as one month, but often after 4 if they are both healthy. If there are fertility problems but the woman is still ovulating, a couple who can determine their fertility can conceive within 8 months on average. Of course, that last stat can vary a lot depending on how often a less fertile woman ovulates.
Let's continue now onto the next phase of a woman's fertility: pregnancy. We all know that women carry their children on average 40 weeks, but it is really more like 41 weeks for first time mothers. This varies depending on your race and health conditions, but is pretty static over all.
Pregnancy benefits the woman's over all health by giving her ovaries a rest. The monthly surges of hormones are relieved and replaced by a steady increase of the hormone progesterone, which I like to call "the happy-hormone" because it really makes you feel good, you know that thing they call the "pregnancy glow"? In fact there have been a few studies which link post-partum depression and the length of pregnancy since progesterone levels peak right at the end of pregnancy and then drop to nearly zero after birth. Theoretically, if a woman has not been pregnant for the 40 to 41 weeks her level of progesterone will not reach that peak and will therefore be lower over all and the after birth change will not be as drastic.
The other benefit of pregnancy is the lowered risk of cancers in her fertile system, such as breast and ovarian cancer. Pregnancy gives your body a rest from the back and forth high levels of estrogen, which is a cancer causing hormone in too high of levels. That's pretty cool, too, if you ask me.
Once a woman has given birth we begin the next phase of her fertility. And it's not "trying not to get pregnant too soon." God has made a natural way to space our children, and lucky for us it has sooooooo many other benefits for mom and baby that you'd be silly not to give it a try.
This is, of course, breastfeeding which I will discuss in my next post. I think I've already given everyone enough to chew on for one day. :)