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How your chances of conceiving are affected by your cycle, age, birth control, health conditions (and more)

How your chances of conceiving are affected by your cycle, age, birth control, health conditions (and more)

14 min read

Depending on what state, county, or school district you grew up in, what you were taught about reproduction and conception varies greatly. Though 39 states and DC require some sort of sex education, only 44% of states mandating sex ed require that content be medically accurate. (It’s a real head scratcher.) While some teens learn that abstinence is the only way to avoid conceiving, it turns out that abstinence-only education actually harms teens by leading to increased rates of teen pregnancy and sexually transmitted infections.

In this post, we’ll go way beyond your high school sex ed to give you the (medically accurate) summary on your chances of conceiving, and how those chances are affected by things like: your cycle, age, previous and current birth control use, conditions like polycystic ovary syndrome (PCOS), and more.

Whether you’re actively trying to conceive (TTC) or actively avoiding conception, we want you to have the info required to help you achieve your reproductive goals — whatever they may be.

The data, in a nutshell

  • There’s a 42% (max) chance of conception on the day before ovulation, the most fertile day of your cycle. (Source)
  • On average, 68% of women aged 20-44 will conceive within three months of TTC, and 92% will conceive within 1 year of TTC. (Source)
  • 45% of people age 25 or younger conceive within one cycle; while 20% of people age 35 or older conceive within one cycle. (Source)
  • Compared to women who’ve never used birth control, there is a 0% difference in pregnancy rates after 12 months for ex-pill and ex-IUD users. (Source)
  • The failure rate (how many women get pregnant over the course of a year) for long-acting reversible contraceptives like IUDs is 1%.
  • 10% of women have PCOS, a condition that is associated with irregular and infrequent ovulation, making natural conception trickier.

Back to basics: What is conception, anyway?

Conception is a little more nuanced than the love story of egg meets sperm, sperm meets egg, and — voila! — conception. Of course, it’s true that the meeting of eggs and sperm is a necessary prerequisite to a pregnancy, but let’s get into why it’s a bit more complicated than that.

While we’re born with all the eggs we’ll ever have (over one million!) and have approximately 400,000 eggs left by the time we hit puberty, almost all of these eggs are suspended in an undeveloped state — it’s only in the few months before an egg is ovulated that it grows and develops into an egg that can be fertilized.

Around ovulation, typically one egg is released from the follicle it grew and developed in. It takes an egg about 30 hours to travel from the ovary to the end of the tube. The egg rests there, and then it waits another 30 hours. After 24 hours, if fertilization doesn’t occur, RIP to that egg.

If any sperm were waiting around in the reproductive tract before ovulation occurred (they can survive in the female reproductive tract for up to around five days, after all), or if sperm make their way into the reproductive tract and all the way to the egg when it’s released, fertilization can occur.

Most medical professionals agree that a fertilized egg does not equal successful conception. It takes about six days for a fertilized egg to travel down into the uterus where it then digs its heels into the uterine lining (on average, fertilized eggs implant 6-10 days after conception in the fallopian tube).

It’s only at that point that it can start further developing and receiving the nutrients it needs to result in a pregnancy. Only about 40% of fertilized eggs will make it past this implanting-in-the-uterine-lining hurdle (caveat: this data is hard to come by, so estimates of this statistic may vary widely), and it’s after that point that most medical professionals would consider it a pregnancy.

How your hormones change before, during, and after ovulation
Here we’ll explain how estradiol, luteinizing hormone (LH), and progesterone levels all fluctuate — and what tracking each of these hormones can tell you about ovulation.

What are the chances of conception during your cycle?

If you get your period regularly and don’t have any conditions like PCOS that influence ovulation, you’ll ovulate around the middle of your cycle (days 10-14), in about 92% to 96% of cycles; in the remaining 4-6% of cycles, ovulation never occurs (this is perfectly normal).

In a cycle where ovulation occurs, recent estimates suggest the chances of conception are between 3% seven days before ovulation and 42% the day before ovulation. Estimates from other studies suggest peak chances of conception are a bit lower — closer to 38% according to some, or 20% according to others. Differences in study methodology and the demographics of the women who are in their sample (e.g., age, if women with any reproductive conditions were screened out) may in part explain the variation in estimates among studies.

Because sperm can live up to five days in the female reproductive tract, it *is* completely possible to get pregnant if you have sex on the days leading up to ovulation and not on the day of ovulation itself, if those five days overlaps at all with the 24 hours that an egg can be fertilized. Having sex on the days leading up to ovulation, even though ovulation has not yet occurred, makes it likely that there will be some sperm waiting around for the egg once it’s released. That being said, chances of conception get higher the closer you get to ovulation.

Outside the “fertile window” (i.e., the seven days before ovulation, the day of ovulation, and the day after ovulation), it is not physiologically possible to conceive if you have regular-length cycles and periods. This means that you can’t get pregnant while on your period, nor can you get pregnant several days after you’ve ovulated. This changes if your follicular phase is abnormally short. Having said that, remember that not every woman ovulates on day 14.  If you ovulate on day 9 or 10, that means you can get pregnant from sex you had on day 4 or 5 of your period (#math).

How long, on average, does it take to conceive?

For your average uterus owners who haven’t been on any birth control for a while, according to one large study of women between the ages of 20 and 44, about 38% will conceive within one month of TTC, 68% within three months, 81% within six months, and 92% within 12 months. This means that among couples who are TTC and have not conceived in the first six months, only half of these couples will conceive in the next six months. Other studies have come up with slightly different estimates, with some suggesting that the percentage of women conceiving within the first 12 months is closer to 84%.

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How does birth control impact the time it takes to conceive?

If you have recently stopped using a non-barrier-based method of birth control (i.e., not spermicide or condoms), these numbers may look a bit different depending on what you were using.

A team of researchers recently did a systematic review of the existing work on how different methods of birth control impacted the likelihood of getting pregnant within 12 months of TTC. Here’s what they found:

  • 74.7% for ex-implant users
  • 77.74% for ex-injectable users
  • 87.04% for ex-oral contraception users
  • 84.75% for ex-IUD users (there's no difference between hormonal and non-hormonal IUDs)

Among women using different formulations of oral contraception, times to conception are similar — meaning how soon you’re likely to get pregnant after stopping the pill isn’t affected by whether the pill was a combined oral contraceptive or the progestin-only pill, or by the pill dose. Time-to-pregnancy is also likely not affected by the duration of oral contraceptive use.

The main takeaway here? There’s no delay in the resumption of fertility for women coming off of the most popular methods of birth control, but women coming off of the implant and injection-based methods may see a slight delay. This no-delay-in-resumption-of-fertility also doesn’t seem to be affected by how long contraception methods were used for. For more info, you can check out this post that covers birth control’s impact on fertility.

Is there a chance of conceiving if you’re currently on birth control?

Chances are, if you’re currently using birth control, you’re not TTC — but how successful your birth control method is at preventing pregnancy differs significantly based on what you’re using.

The effectiveness of birth control methods are measured in two ways: One way focuses on perfect use (i.e., how effective is this method if people use it exactly how it is meant to be used?) and the other on typical use (i.e., how effective is this method given how people use it in the real world?). Here, we’ll focus on typical use because it is more real-world relevant.

According to the Centers for Disease Control and Prevention (CDC), the least effective birth control method is spermicide — of couples who only use this method over the course of a year, 28 out of 100 will experience an unintended pregnancy within the first year of typical use.

This number falls to 18 out of 100 over the course of a year for condoms, and further drops to 9 out of 100 for the pill, the patch, and the ring. While a 9 in 100 failure rate seems high for these hormone-based methods, it’s important to remember that this rate takes into account user error. Because women do not always take the pill as directed, and do not replace their patches and rings when they’re supposed to, failure rates for these methods are higher than they would be with perfect use.

There are some birth control methods that require less action on the part of women; for example, once you get an IUD, there’s nothing you have to do to make sure it’s doing its thang, except for remembering to get it replaced every 3-10 years (depending on the type you get). These methods, called long-acting reversible contraceptives (LARCs for short), have failure rates of less than 1%.  

How are cycle-based conception rates and time-to-pregnancy affected by age?

If you’ve read some of our previous blog posts on aging and fertility or have used our Timeline Tool, you likely know that fertility decreases as women (and men!) age. These changes in fertility are a function of both how many eggs we have left, and how healthy those eggs are. Together, the changes in egg quality and quantity make it trickier to conceive as age goes up.

There is some data from large-scale studies investigating the effect of age on cycle-based conception rates. According to one study from 2002, the chances of conception during the “fertile window” decrease as age increases. For example, while this study estimated the chance of conception at two days before ovulation to be roughly 50% for women between the ages of 19 and 26, it was less than 30% for women between the ages of 35 and 39. Other studies have mirrored these findings, showing that cycle day-specific conception probabilities in the “fertile window” are lower among older women.

Time-to-pregnancy may also differ among women of different ages — based on one set of estimates, while about 45% of women 25 or younger may conceive after one cycle, this stat is closer to 20% for women over 35. Another study estimated that 92% of women age 19-26 will successfully conceive after one year of trying to get pregnant. That number decreases to 86% for women age 27-34, and 82% for women age 35-39. (Note: This study uses narrower age brackets and data from one sample only.) While this data doesn’t suggest that conception rates after 12 months of TTC take a nosedive between the ages of 19 and 39, they do suggest a robust relationship between age and fertility in women.

The main takeaway here? Your chances of conceiving on each day of your “fertile window” change as you age, and this may in part explain why time-to-pregnancy is longer among older women.  

How do medical conditions impact my chances of conception?

Different medical conditions may (or may not!) impact how often you ovulate, how likely a fertilized egg is to implant, and how likely a pregnancy is to be carried to term. Though there are lots of medical conditions that might affect conception, here we’ll focus on three that are common and often undiagnosed: PCOS, endometriosis, and thyroid conditions.

PCOS and conception

PCOS affects 1 in 10 women, and is one of the leading culprits of infertility among couples seeking treatment at assisted reproduction clinics. In women with PCOS, ovulation is irregular and occurs less frequently. This means that women with PCOS ovulate infrequently (if at all), and ovulation doesn’t always occur at predictable intervals.

There are science-backed, FDA-approved options for women with PCOS to boost their chances of conception that work by improving the frequency and regularity of ovulation. Clomid administration increases the chances of ovulation in women with PCOS, and metformin may too. Women with PCOS are at increased risk of adverse pregnancy outcomes which means they may need additional visits with their doctor when trying to conceive and after conception has occurred.

Endometriosis and conception

Endometriosis is a condition characterized by the growth of endometrial tissue outside of the uterus, and may manifest as excessive cramping, pressure, bloating, headaches, and bleeding. Somewhere between 6 and 10% of women have endometriosis, and among women with infertility, up to 50% may have endometriosis (whether it be diagnosed or undiagnosed). According to the American Society of Reproductive Medicine (ASRM), the hypothesis that endometriosis causes infertility is controversial. What’s not as controversial? That the reproductive hormone-based medications prescribed to help deal with the symptoms of endometriosis may not be an option for women who are TTC, as they’ll disrupt your ability to conceive. In these cases, surgery or assisted reproductive technology may be the way to go — though a recent ASRM committee opinion has highlighted that there are mixed findings about how effective these options are.

Thyroid dysfunction and reproductive health

Your thyroid gland is regulated by the hypothalamus-pituitary axis (HPA) — a dynamic duo featuring the hypothalamus (a part of the brain that produces hormones) and the pituitary gland (which waits for its cue from the hypothalamus). When something happens in one area of the HPA, it often triggers a chain reaction in other areas. What this means: When there are higher or lower levels of thyroid hormones, it can alter our reproductive hormones and disrupt the menstrual cycle — which makes conception more difficult. But just because you have hypo- or hyperthyroidism doesn’t mean you can’t get pregnant. In one study of a group of almost 400 women suffering from infertility, 24% of participants were found to have hypothyroidism — but within a year of treatment, 76% were able to conceive.

Prescription medications and conception

It’s also possible to have a medical condition that doesn’t affect ovulation or fertility, but to be on medications for that condition that do. For example, there’s no reason to think that women with mild musculoskeletal pain would have issues with ovulation. But, a recent study showed that the medication used to treat pain in a group of these women — nonsteroidal anti-inflammatory drugs (NSAIDs) — decreased progesterone levels and impaired ovulation, both of which negatively impact chances of conception. There’s also evidence that medication for mental health conditions, like antidepressants, can have an effect on fertility.

If you have a diagnosed medical condition or are taking prescription meds, talk to your doctor before TTC. They will be able to give you crucial insight into how your diagnoses and meds may impact your chances of conception (if at all), and suggest steps to help you maximize those chances.

How can I increase my chances of natural conception?

Ah yes, the million-dollar question. Because there are many factors that influence your chances of conceiving, there are several different things you can do to tip the scales in your favor.

Arguably the most important thing you can do to boost your odds is to track your cycles and time intercourse around ovulation. After all, if you aren’t having sex during the fertile window, your chances of conception are zero. Because the chances of conception increase in the five days before ovulation and peak the day before ovulation, you should be having sex within this window if you’re looking to conceive. While some sources suggest you should be having intercourse every other day in this window, there aren’t empirical studies suggesting what the optimal intercourse frequency is, but it’s likely that more frequent = better.

To figure out where in your cycle you are, you can use ovulation prediction kits (OPKs), aka ovulation tests, which use hormones (specifically, luteinizing hormone) to tell you whether you’re ovulating. The Modern Fertility Ovulation Test identifies your LH at low, high, or peak levels. Tracking your LH daily gives you more insight into your fertile window and ovulation patterns than you’d get with standard ovulation tests that give positive/negative results. (Those tests are based on LH averages, which don’t apply to 1 in 10 of us.)

You can also use so-called “sympto-thermal” methods of cycle tracking, which involve taking your temperature (the “thermal”) and examining certain symptoms (the “sympto”) like your cervical mucus consistency to pinpoint when your “fertile window” starts and ends. Previous work has shown that cycle tracking using these symptoms can increase chances of pregnancy among TTC women, both those who have and have not had difficulty conceiving.

Certain lifestyle factors may also modulate how likely you are to conceive because they affect how regularly you ovulate, your egg quality, and your ovarian reserve. For example, having a very low or high body-fat percentage might make conception trickier. Another thing that makes it tricker? Smoking (that includes vaping!) and THC affect the gametes (another word for sex cells; eggs for women, sperm for men) of both sexes.

Summing it all up

There are so many factors that affect the likelihood of conception that sometimes it may seem like a miracle it happens at all. Putting it all together, here’s what we know about chances of conception:

  1. Because of how long sperm can live in the female reproductive tract and how long an egg can be fertilized, it’s possible to conceive only during a specific time of the cycle. The chances of conception increase as you get closer to ovulation.
  2. The chances of conceiving on each day of the cycle differ a bit based on your age — with younger age → higher chances. Because of this, time-to-pregnancy changes with age too.
  3. Used pills, injections, patches, IUDs in the past? There’s no evidence that these should affect your odds of conceiving in the long run, but time-to-pregnancy is slightly longer in those who recently stopped using injections or implants.
  4. Certain medical conditions like PCOS and endometriosis make conception trickier. If you think you may have one of these conditions, it’s best to see an OB-GYN or reproductive endocrinologist.

While we can’t control things like our age or diagnoses, there are steps you can take to better understand your fertility and boost that likelihood of conceiving.  We offer a few different ways to do that:

  • The Modern Fertility Hormone Test measures the same fertility hormones that a doctor would test in a fertility clinic (for a fraction of the price) and helps you understand how your fertility is changing over time. Our hormone test gives you insight into the number of eggs you have and can help you identify red flag issues — like PCOS or thyroid conditions — that could affect your reproductive health down the line.
  • The Modern Fertility Ovulation Test helps you pinpoint your LH levels to predict your 2 most fertile days. With our test, you’ll get more insight than just a positive or negative result — you’ll be able to see your LH change daily and track low, high, or peak levels. This is key for understanding whether you're in your fertile window and approaching ovulation (when you have the highest chances of pregnancy).
  • The Modern Fertility App helps you find your fertile window more easily by logging and tracking your periods, sex or insemination, and Ovulation Tests.
  • And once you’re ready to test for pregnancy… the Modern Fertility Pregnancy Test is just as accurate from the day of your missed period as leading pregnancy tests — and it’s more affordable. It also works like magic with our app.

Along with our at-home tests and digital tools, you can also track your temp and cervical mucus for additional ways to pinpoint ovulation and time intercourse accordingly, and embrace healthy lifestyle habits.

This article was medically reviewed by Dr. Jane van Dis, MD, FACOG. Dr. van Dis is an OB-GYN, co-founder and CEO of Equity Quotient, and Medical Director for Ob Hospitalist Group.

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Talia Shirazi

Talia is a biological anthropology PhD candidate at Penn State, passionate about women's reproductive health and behavioral neuroendocrinology.

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