Fertility 101

Generally speaking, if a person is under the age of 35 and is unable to conceive after 12 months of trying (or 6 months of trying for those 35 and older), a fertility evaluation is recommended. These thresholds may be further reduced in light of a known cause such as male factor or irregular periods.

If you’re confused about how long it “should” take to get pregnant, you’re not alone. When it’s been studied, we see that the vast majority of people have misconceptions about how long it should really take to achieve a pregnancy.

The true chance of pregnancy peaks between 26%–38% per cycle at a maternal age in the early thirties, depending on which study you look at. Importantly, after every cycle when a pregnancy doesn’t occur, the chances that a pregnancy will happen the next cycle decrease.

Looking at the Zinaman study below—which only followed women ages 37 or younger—between three to six months of trying to conceive, the rates dipped down into the teens, and thereafter, rates dip into the single digits. This study followed 200 couples, and around 82% of the couples in this study, conceived during the 12 month period.

What’s also notable is that all of these studies demonstrated a relatively fast time to pregnancy for most people. Between these differing studies, by 6 months, 65%–81% of women conceived and by one year, 78%–92% of couples conceived.

The Gnoth study also noted that 98% of all couples who would go on to conceive naturally conceived in those first 12 months. So if conception doesn’t happen by 6 months and certainly by 1 year, there is a good chance it won’t happen without help, and you need to get to a clinic.

Another thing these studies show us: being disciplined about timing intercourse matters. In the Gnoth and Zinaman studies, the timing of intercourse was rigorously planned, and the two studies recorded the conception rate at 38% and 30% in the first month respectively. This percentage is far higher than what’s found in other studies.

Of course, remember that this is just conception, not live birth—in fact, Zinaman saw 30% of all those conceptions terminate before live birth. We’ll discuss the role of miscarriage later.

Finally, it's important to note that these statistics are not necessarily applicable in cases where there is a known infertility etiology (such as blocked fallopian tubees or azoospermia).

Time to Pregnancy by Age

Unfortunately, the ability to conceive each month goes down as women get older. You can see the chart below with data from Steiner’s study for full details, but to illustrate the point: after 12 cycles, 88% of women ages 30–33 conceived, and 54% of women ages 40–41 conceived.

One weakness of this study is that there weren’t very many women who were between 40 and 44 years old. But even with these relatively small numbers, we’re able to observe this important trend.

Age: Pregnancy & Miscarriage

It’s impossible to think about time to pregnancy and rates of pregnancies that result in live births without taking into account the role of female age.

Male age plays a much smaller, and less defined role in conception, so here we’re just going to be focusing on female age.

If you’re interested in the role male age plays, you can see our dedicated lesson here.

Miscarriage Goes Up With Age

The painful reality is that not every pregnancy results in a live birth. In the Zinaman study, data shows nearly one third of pregnancies ended in losses for those who were 37 years old and younger (it’s important to note that participants were capped at 37 years old in this study). That number increases substantially with age as uneven egg division (leading to chromosomal abnormalities) of a mature egg also increases with age (as noted in lesson 2). So the unfortunate news to deliver is that as women age, it gets harder to get pregnant in the first place, and it also becomes much more likely that those pregnancies will stop short of a live birth.

Below, you can see some data from a study conducted on the general population of Norwegian women. Miscarriage rates were the lowest for women ages 25–29 at just under 10% of pregnancies ending in miscarrige. As maternal age increased, so did the miscariage rates—revealing that over half of all pregnancies ended in miscarriage for women who conceived at 45 years old and older.

When it comes to getting pregnant “the old fashioned way” timing is everything — intercourse needs to happen during “the fertile window” or a pregnancy won’t be possible. But, even amongst women who monitor for ovulation, a study showed only 18% properly identified the fertile window! (Righarts A et al. 2017).

While that might be hard to believe, it means we’re going to take this from the top and cover how to monitor a menstrual cycle and when it’s the best time to have sex for conception.

First, though, let’s revisit the menstrual cycle to understand how it relates to pregnancy planning.
The first day of bleeding during a period is considered day one of the menstrual cycle. At this stage, there should still be many microscopic follicles (that contain immature eggs), lying dormant within the ovary. Eventually, one follicle will be selected as the strongest or “dominant” follicle that will be ovulated—that follicle will produce estrogen. Some ovulation predictor kits measure estrogen levels and, when estrogen levels rise, they’ll indicate a “high fertility” phase, though this is well before ovulation.

Ovulation refers to the maturation and release of an egg from the ovary—the follicle that held the egg ruptures, and the fallopian tube sweeps the surface of the ovary to bring it into the tube. On average, this happens on day 14 of a 28-day menstrual cycle but will vary for longer cycles which, as previously described, have longer follicular phases and generally fixed luteal phases.

A hormone called luteinizing hormone, or LH, provides the stimulus to start the process of ovulation. Once LH levels rise high enough—called the “LH surge”—it signals that ovulation will occur within 36 to 40 hours. That’s why many home ovulation predictor kits (OPKs) measure LH levels showing “peak fertility” when LH is high.

Once ovulation happens, an egg can only be fertilized for a very short time—less than a day! This is crucial to understand because it means that sperm should ideally be there, ready and waiting for the egg to be released, at or even before the time of ovulation.

Unlike an egg, sperm can generally live in the female reproductive tract for a few days. This is why it’s best to make sure you’re having sex in the one or two days before ovulation.

This study from the New England Journal of Medicine answers the question—if you only had sex one time during the month when trying to conceive, what is the chance of pregnancy on each day? The investigators followed couples who had sex only once in the days leading up to ovulation and tracked their probability of conception. As you can see, those who had sex in the two days leading up to ovulation recorded good pregnancy rates, and those who missed the window by a day had none.

This showed a probability of conception of nearly 10% when intercourse happened five days before ovulation and 36% when intercourse happened on the day of ovulation itself.

This chart also helps to clear up one of the most common misconceptions about getting pregnant—in fact, a woman’s fertile window is just a few days before ovulation rather than ovulation signalling the beginning of the window.

Of course, there is absolutely no reason to have sex only one day when you’re trying to conceive. There are lots of old wives tales out there about not wanting to have sex too often for fears of diminishing sperm count (more on that later). But if you try and “save up”, there’s a real risk that trying to only have sex one time at the perfect moment means you could miss the window altogether. Having sex once per day or every other day in the lead up to ovulation is probably a good idea!

Given the importance of timing in terms of when intercourse can lead to pregnancy, it makes sense for a woman to monitor her menstrual cycle so she can know in advance when ovulation is likely to happen, and be sure to have intercourse in the days leading up to ovulation.

The most reliable way to predict ovulation for most women, short of going to the doctor for ultrasounds or blood draws, are at-home ovulation predictor kits. These kits, “OPKs” for short involve peeing on a stick—those sticks measure the hormone levels found in urine. Some of these tests monitor LH only, which is the hormone that spikes immediately before ovulation—meaning intercourse is advised as soon as you see the LH spike.

Other tests also measure rising estrogen levels. Estrogen gets higher as the main follicle and egg chosen for development in a given cycle grows and matures, so crossing a test’s estrogen threshold means ovulation should happen within a week. This is a less urgent message than seeing an LH spike, and generally signals that intercourse every day or every other day for the next week is a good idea.

It’s important to note that home ovulation predictor kits do not work equally well for all women. For example, women with PCOS tend to have high levels of LH throughout the month, so they might get false positives on OPKs that tell them they’re going to ovulate, when they’re really not. Additionally, women with severely diminished ovarian reserve can also have elevated LH levels throughout the cycle. Finally, treatments like clomid might cause LH levels to be higher than they otherwise would be, so some patients consistently get confusing OPK results—if this is the case, then monitoring another way, like ultrasound and blood work at the doctor’s office, might make sense.

After months or more of trying, these kits can get expensive. It’s possible to buy in bulk online, purchasing the less-expensive testing paper without the fancy digital readers. If you’re price sensitive and want to monitor frequently, this could be a good idea.

Apps, Wearable Devices, & Fertility Technology to Track Ovulation

There have been a number of fertility technology products, cycle tracking apps, and wearable devices coming out lately.

As far as apps where you enter information about your period, these can be helpful tools in terms of giving you a sense of your average cycle, and bringing up red flags about irregularity. But just know, they won’t be precise like using an OPK will.

When it comes to wearables, anything that relies on temperature will only give you information that you’ve already ovulated. Some wearables track more than just temperature. It’s possible that these tools can and will be helpful in the future, but at this point, we don’t have good data on how accurate they are.

New to the market are at-home tests that provide quantitative (or semi-quantitative) tracking of hormone levels. Urine is used to measure specific hormone levels (like LH, estrogen, or progesterone) and are reported in an app.

On the plus side, tracking hormone levels throughout the month gives a more realistic picture of a woman’s actual cycle—not just based on the 28-day “standard” cycle—and may have an advantage against an OPK. It’s important to note, however, that these tools are a new addition to the field of at-home testing, and data about the outcome of these tools are still being formed (though the initial data seems positive).

Less Reliable Means of Predicting Ovulation

One old-school strategy for predicting ovulation is monitoring the changes in discharge, or cervical mucus, that occur during the month. As estrogen peaks before ovulation, cervical mucus becomes clear, stretchy, and copious.

The good news is this strategy is free. The bad news is that it’s not very accurate. One study by Fehring showed that only 58% accurately identified the 72-hour window before ovulation, which is only slightly better than flipping a coin.

Another strategy is checking and charting basal body temperature or BBT. To be absolutely clear, tracking BBT does not predict ovulation within a current cycle. BBT can tell you when you have already ovulated but you can’t use that information this cycle. It can only be applied, assuming your cycles are regular, to timing intercourse during the next cycle.

Charting BBT involves taking your temperature at the exact same time every morning, before moving around at all. It relies on the premise that as progesterone rises following ovulation, temperature rises a little bit too. Because this strategy is (1) a lot of work; (2) easy to get wrong; and (3) doesn’t help to actually predict before ovulation happens, we’ll call this one a waste of time and energy.