Just the other day, a young woman stuck up a conversation with me at the dog park while our dogs were playing. When she learned what I did for a living, she excitedly told me "It's great I met you! My husband and I want to start trying for our first baby next year, so I've been meaning to get ready by learning how to take my temperatures. Do you have any suggestions?" As it turned out, she had many girlfriends who were trying to conceive and were always talking about taking their temperatures, charting their cervical mucus , scheduling their times of intercourse and all that. She sounded almost surprised when I shared with her that for most couples, meticulously trying to time their intercourse is a waste of time (with a few exceptions which I'll cover later on in this post).
Let's start with some basic concepts. Every couple has their own magic number that represents their FERTILITY ODDS for that month assuming they have sex every 2-3 days without paying attention to timing. For a couple in their early 20's with excellent sperm and perfectly clean Fallopian tubes and with the wife being an overachiever who ovulated not one, but two eggs that month, their fertility odds (FO) that month might be 50%. (By the way, it's not standard to ovulate two eggs in one month, but there are women out there in which a lot of fraternal twins run in their families. These women could potentially ovulate double from time to time.) While this lucky fertile couple have a really high FO, contrast this to her next-door neighbor, who is 39 years old, overweight, with irregular periods, endometriosis and one blocked tube and a husband who smokes 2 packs a day. Their FO is less than 1%.
In general, the FO in a given month for a couple of average fertility is about 20-25%. But remember the concept of averages. The average American woman is 5'4" tall. However it's not uncommon for women to be significantly shorter or taller than that. Likewise, there are some couples who are super fertile and have higher FO above 30% and others who are subfertile with FO of 5%. In general, couples with high FO's don't obsess about basal body temperature, cervical mucus nor ovulation kits, because they don't have time to do that in between all the babies they have. These are couples for whom pregnancy comes to them right away the moment they get lax about contraception. Couples with average FO's may or may not get to the point where they start stressing about ovulation timing, depending on how lucky they are. For example, compare having a FO of 25% and trying to conceive to playing a simple game with a deck of cards in which the rules are as follows. Every cycle, you shuffle the cards and draw one card at the time of ovulation and hide it in an envelope. You don't get to reveal that card until 14 days later. When you finally do get to see it, if it is a heart, then congratulations! You are now pregnant. If it is not a heart, then your period starts. You place the card back and put the deck away until next month. I'm sure many of you can imagine what it is like to play this game. Now, if you have normal fertility with a normal 25% FO, then you play with a normal deck of cards and it's almost for sure that you will eventually draw a heart, most likely before playing this game for six months. Still, even if you are normal, but just unlucky, you COULD possibly go on a cold streak and draw 7 or more cards and still never get a heart. However, in time, the odds will even out and you will eventually get your heart.
So what happens if you end up playing this game for three years and still never draw a heart. Obviously, your first suspicion is that you are not playing with a normal deck. Maybe only 2% of the cards are hearts, meaning you'll have to play this for a lot longer before you finally draw a winner. Worse still, maybe there are no hearts in your deck at all, meaning all this time was a waste and the only way you can get pregnant is with medical treatment. Or what about women who don't ovulate. For them, it's like not getting a chance to draw a card at all!
So, after all this background info, I'll now return to the topic of timing intercourse with one's ovulation. OK, stay with me here. As we have just gone over in great detail, every couple has a specific FO each month. The factors that affect your FO include passive factors for which you don't have instant control (age, weight, whether the tubes are blocked, sperm count, overall wellness) and active factors for which you DO have control, primarily when you have sex.
So let's assume that you and your husband have a 25% FO.
Here are the key points:
1. If you have sex every 2-3 days, your odds of pregnancy that month are 25%.
2. There is a certain day that you are most fertile. If you actually have sex on that day of peak fertility, you might be able to bump your odds up above your regular FO to maybe 30%. You might realize that if you just have sex every 2 days, you'll probably hit that day of peak fertility half the time anyway, without all the bothersome charting.
3. If you DON'T have sex at all in the 4 days leading up to and including your peak day, you drop your FO to 5% that month.
4. If you don't have sex in the 6 days leading up to and including your peak day, you drop your FO below 1%.
So how does meticulous timing affect your chances? It depends on how you do it.
METHOD A: Some couples have sex every 2-3 days anyway, but use ovulation timing to make sure they get together on what they believe to be their one peak day. If they are correct about the peak day (and chances are actually good that they are NOT always accurately predicting the perfect peak day despite all the charting and ovulation predictor kits) then they can boost their chances that month from 25% to 30%. If they guess wrong about the peak day, then they are back to their normal 25%.
B: Other couples deliberately try to abstain until what they think is their peak day. Wives tell their husbands to stay away and save up their sperm until they are given the green light! In this case, if your prediction methods are accurate, then you have a 30% chance that month. If you guess wrong and are early by one day, you have a 25% chance. BUT, if you guess wrong and are late by 1 day, then you have less than a 1% chance!! Why is this? Because if you have sex only AFTER you ovulate, even if the egg is still viable, the cervical mucus undergoes changes to shut out sperm from coming in. After the egg has already released, you can still get pregnant through insemination, thereby using a catheter to bypass the hostile mucus, but studies show it's almost impossible to get pregnant through natural intercourse if it's done only AFTER the egg has released.
So you see, in scenario A, trying to time things might only help a little at best, while most of the time it doesn't change your odds at all. In scenario B, if your timing is accurate, it might help a little or be the same, but if your timing is inaccurate, you have now disastrously LOWERED your chances.
Therefore the best general strategy is to have sex every 2 days, especially in the week leading up to your time of ovulation.
I'll close by fulfilling my earlier promise to list the instances in which monitoring your ovulation is NOT completely worthless.
1. If it relaxes you and lowers your stress to feel like you're doing something. A lot of times, women find great social support from discussing their temperature and charting with other women who are trying to conceive. Anything that lowers stress can contribute to higher FO. It also reassure you about the likelihood that you ARE ovulating. If your monitoring activities clue you in that you're not ovulating, then you will be alerted to seek help before wasting too much time.
2. If you are a couple who have sex only once or twice a month and just cannot for whatever reason make it feasible to have sex every 2-3 days, then it WOULD be useful to employ ovulation monitoring to help you focus on the days that really count.
But remember, if ovulation monitoring CAUSES you more stress or if you do it wrong and it causes you to miss your peak day, then it is clearly harmful to your chances.
The woman at the dog park was herself in a job where she was trained to think analytically and scientifically, so she loved learning this detailed information. She joked about how we humans have evolved into a species for whom normal reproduction requires the act of taking temperatures. By this time, our dogs were exhausted. She thanked me profusely and asked for my contact information. She also thanked my dogs for enabling our chance meeting.
By the way, here is a video of my dogs, Brandy and Ixie, engaged in friendly combat. =)