It’s hardly ever talked about … but it can be of vital importance. During a crisis, access to normal health care, including contraception, might be interrupted. It might be a really bad time to add a baby to the family (Or might not, but decisions generally work better than accidents). On the other hand, people’s desire for sexual intimacy will not necessarily go away.

What’s to be done?

Abstinence is 100% effective if you don’t think it’s the right time to have a child; but you knew that so I won’t belabor the point.

One can stock up on contraceptives while they’re available (at least some sorts). That approach is worthwhile but limited. They will be used up or age out of usefulness. All the alternatives that are left have serious drawbacks, but they’re a lot better than nothing. So let’s take a look at the foremost remaining option, what’s usually called ‘natural family planning’. This isn’t just a euphemism, by the way. Once you understand how the cycles work, you can choose either the behaviors that make conception more likely, or less. Men are fertile basically every day from puberty to death, so it’s the woman’s cycle that provides the options.

How the cycle normally works

Starting on day one of her cycle (the day menstruation begins), a woman starts developing the Egg of the Month while she develops the lining of her uterus in case it needs to support an embryo later. Around Day 14, the egg is ready and leaves the ovary to start travelling down her tubes toward the uterus. This event is called ovulation. Ovulation is significant because if a pregnancy is to occur, that egg must be fertilized some time in the next several days. Since sperm can survive in the woman’s reproductive tract for about five days, there’s a window of opportunity that begins several days before ovulation and lasts several days afterwards where sex is most likely to result in pregnancy.

If the egg is fertilized on its way down the tubes, it starts dividing and the tiny embryo attaches to the lining once it arrives in the uterus and the placenta develops. The brand new placenta releases a hormone that pauses the woman’s menstrual cycles. This is how successful pregnancies start. (Home pregnancy test kits are checking for that hormone in the woman’s urine.)

If there is no embryo and no placenta making that hormone, about two weeks after ovulation the extra build-up of uterine lining is shed (menstruation begins) and a new cycle starts.

How natural family planning works within this setup

In concept, it’s not so hard. If you don’t wish to be a parent, avoid sex during the window of opportunity that occurs around the time of ovulation. If you want to be a parent, that’s the best time to get intimate. The trick is knowing when ovulation is going to occur.

Women vary from each other: four week cycles are average, but a particular woman’s average might be anywhere from three to six weeks. This is why natural family planning includes having the woman mark her cycles on a calendar regularly.

An individual woman also varies. Some women aren’t very regular at all, making natural family planning less reliable for them. Others are more regular, and the method works better for them. However, stress and illness can upset any woman’s clock. This is the main reason why natural family planning methods are not highly reliable. More on reliability below.

The calendar method

The woman charts her cycles for at least six months to get a feel for her own cycles, then avoids having sex near the projected ovulation time. The Mayo clinic offers a specific set of instructions for using the calendar method here: http://www.mayoclinic.org/tests-procedures/rhythm-method/basics/what-you-can-expect/prc-20013489

The body temperature method

This method relies on the fact that a woman’s body temperature upon first awakening in the morning varies with her cycle. It goes up just a small amount (about one degree F) when she ovulates. To use this method, she takes her body temperature every morning before she even gets out of bed and charts it. When it goes up that degree or so, she knows she’s ovulated. Starting four days later, she’s pretty safe to have sex without getting pregnant until her next period.

How reliable is natural family planning?

It depends on if you compare it to no planning at all (85% pregnancy per year) or a really effective method. If these methods are followed perfectly, pregnancy rates can be as low as 5% per year. (I wouldn’t count on it working that well during stressful times; cycles get less reliable.) Real people using it imperfectly as real people do have about a 24% per year pregnancy rate. That’s probably pretty close to what a woman can get using a diaphragm if she doesn’t have spermicide to use with it. By comparison, real-life condom use has about an 18% per year failure rate, and The Pill about 9%.

One could also stack methods to increase reliability and/or stretch out supplies. Temperature and calendar together raise the chances to place ovulation accurately. If there’s going to be more activity than the condom supply can support, overall chances of being a parent are much lower if you skip the condom on the far side of the cycle from ovulation, use it nearer to the expected ovulation date, and go fishing instead on the few days closest to ovulation.

Upsides and downsides

As you can see, these methods can’t hold a candle to abstinence if holding off on being a parent is the goal. They also do nothing at all to reduce disease transmission. They require tracking and adherence that many people find difficult. I don’t imagine trying times would reduce that difficulty. On the other hand, if people are going to do what people are going to do anyway, they can reduce pregnancy rates quite a bit, and require no materials beyond paper, pencil, and a good quality thermometer if using the body temperature method. They don’t get used up or lose efficacy due to aging. Also, if the goal is to be a parent, seeking out your partner close to the projected day improves the chances considerably.

*By William Waterway (Own work) [CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons

**Chris 73 / Wikimedia Commons [GFDL 1.3 (www.gnu.org/licenses/fdl-1.3.html) or CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons

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