The definition of infertility

Infertility is defined as an inability to become or remain pregnant after 12 months of regular unprotected sex. It’s recommended that people under 35 try to conceive for a year before seeing a specialist, but because age is so important for fertility, people over the age of 35 should see a specialist if they don’t get pregnant after 6 months. (If there’s a known fertility issue, such as irregular menstrual cycles or endometriosis, it would be appropriate for a person or couple to seek specialist help as soon as they feel ready.)

Infertility is what doctors call a “functional diagnosis.” That means that in most cases—barring rare exceptions in which a person has had their reproductive organs removed, for example—it won’t be diagnosed unless you’ve been actively trying to conceive.

(As a side note: This definition can make things complicated for single people or LGBTQ couples who can’t get pregnant naturally but who won’t receive an infertility diagnosis—and often won’t receive insurance coverage—until they’ve done 3–6 cycles of fertility treatment, a pricey out-of-pocket obligation. Advocates have been pushing for a wider definition of infertility to include “social infertility,” or the presence of non-medical barriers to natural pregnancy, which they hope will expand access to care and coverage.)


In most cases, infertility doesn’t mean you’ll never be able to get pregnant or have a baby, just that you may need medical assistance. According to Resolve, approximately 1 in 8 heterosexual couples experience infertility; roughly a third of infertility cases are attributed to the female partner, a third to the male partner, and a third to a combination of the two or an unknown cause.

Conception requires many functions within the body to go perfectly, which is why even people without fertility issues have only about a 25% chance (or less, depending on age!) of pregnancy each month. Here are the elements required for natural conception, and the issues that could contribute to difficulty getting pregnant:

(Healthy) egg

People with ovaries typically release one egg per menstrual cycle (usually, every 21–35 days). In order to achieve a healthy pregnancy, that egg must be genetically healthy. As you age, the one egg released each cycle has a higher chance of being genetically abnormal, an issue known as low egg quality. Abnormal eggs typically don’t fertilize, but in the case they do, they can cause early miscarriage or congenital disorders like Down syndrome.

In addition to age, premature ovarian failure, a condition in which the ovaries stop working abnormally early (before age 40) can impact the ability to release an egg each month. Smoking affects egg quality and can bring on menopause up to 4 years earlier. Cancer treatment such as radiation or chemotherapy reduce egg quality and the overall number of eggs in the ovaries, and conditions such as endometriosis are also thought to affect egg quality and count.

Learn more about the egg.

Ovulation (and an attempt at fertilization during the ovulation window)

Ovulation is the process by which the egg breaks free from the ovary and travels downward to the uterus. In contrast to what you were probably taught in sex ed, you can’t get pregnant at any time—there’s a 3-day ovulation “window” during the menstrual cycle, typically about halfway through the cycle, in which the egg is released and ready for fertilization. In order to get pregnant naturally, you’ll need to: A. ovulate regularly and B. attempt fertilization during that window.


Age or hormonal balances like PCOS can prevent ovulation from happening normally. There’s also the possibility that you miss your fertile window, especially if you happen to have a particularly early ovulation. Some religious couples, for example, have specific times of the month in which their faith encourages sex—if ovulation falls outside those times, it can be difficult for them to conceive.

Learn more about ovulation.

Cycle tracking can be extremely helpful for people with ovaries who aren’t sure when or if they’re ovulating. Ovulation can be predicted using basal body temperature charting, in tandem with an app like Natural Cycles, or with wearables like the Ava bracelet. A doctor can also tell if you’re ovulating or have ovulated with an ultrasound and hormone blood work.

(Healthy) sperm

Sperm contain the other half of the DNA required for fertilization and natural pregnancy. While only one sperm actually fertilizes the egg, during natural conception less than 1% of sperm will reach the egg at all—so a large number of sperm are required for a realistic chance at natural pregnancy. The factors affecting sperm’s ability to create a pregnancy include the count (total number), motility (movement), morphology (structure), and the genetic health of the sperm.

Age affects sperm health a bit, but unlike with eggs, it’s not the primary factor in male fertility—there are a number of potential causes for poor sperm health, including illness, lifestyle, genetics, medical history, and more.

Learn more about sperm.

(Healthy) environment

In natural conception, sperm and egg meet in the fallopian tubes, the channel that leads from the ovaries to the uterus. Blocked or otherwise unhealthy tubes, which could be caused by scarring from past illness, could prevent the egg and sperm from meeting.

And finally, the uterus must provide a healthy environment for a fertilized egg to implant. Abnormal benign (non-cancerous) growths such as uterine polyps or fibroids are quite common in otherwise healthy people, and their frequency increases with increasing age. Up to 80% of people with uteruses will have a fibroid(s) by age 50.

Learn more about the fallopian tubes and uterus.

What comes next?

The second half of the infertility definition (the one that’s talked about much less) is the inability to remain pregnant. People who are able to get pregnant but have experienced recurrent pregnancy loss often see fertility specialists, but it’s a complex issue—some of the reasons for pregnancy loss, especially early on, are related to fertility, but some are totally unrelated.

In part two of this series, we’ll review pregnancy loss—the different types, possible causes, and potential treatments.