It’s harder to get pregnant than you think. That may be music to your ears if you’re young, single, and nowhere near ready for kids. But for many couples trying to conceive, the reality of infertility is daunting, stressful, and extremely life-interrupting.
“People are always surprised to find out how bad humans are at reproduction,” Alan B. Copperman, M.D., director of the division of reproductive endocrinology and infertility at Mount Sinai Hospital and medical director of Reproductive Medicine Associates of New York, tells SELF. “Not all eggs are normal, not all normal eggs implant. There’s actually only about a 15 to 20 percent chance in any given month that a couple will conceive,” he adds.
In the U.S., 6.7 million women between the ages of 15 and 44 have an impaired ability to get pregnant or carry a baby to term, according to the CDC. About 6 percent of married women 15 to 44 years of age are unable to get pregnant after one year of trying—which is when the “i” word starts to get thrown around, and doctors begin to ask questions and run tests to check the woman’s reproductive system and the man’s sperm count.
“If we look at all causes of infertility, we would attribute the largest cause to male, 40 percent,” explains Meike L. Uhler, M.D., a reproductive endocrinology and infertility specialist at the Fertility Centers of Illinois. Sometimes, it can be the sole cause; other times, it’s just one out of a few factors affecting a couple’s ability to conceive.
So what else could be going on? For women, these are the most common causes of infertility (roughly in order).
1. Polycystic ovary syndrome (PCOS)
PCOS is the most common cause of infertility in women, according to the CDC. The condition is caused by a hormonal imbalance that results in a series of small cysts on the ovaries. It also throws your whole cycle out of whack, causing irregular periods, or even no period at all for a few months at a time. Shockingly, millions of women are living with it without even knowing—according to the PCOS Foundation, 10 percent of women of childbearing age are affected, but less than half are diagnosed. See your doctor if you’re experiencing these subtle signs of PCOS.
2. Other hormonal factors that impact ovulation
Irregular ovulation is the main cause in about 25 percent of infertility cases, according to the Mayo Clinic. While PCOS is the most common of these, causing 70 percent of irregular ovulation-related infertility cases, hormonal imbalances can impact or interrupt ovulation in other ways and lessen your chance of conceiving.
In most of these scenarios, the main culprit is dysfunction of the hypothalamus in the brain and its attached pituitary gland, which is responsible for secreting reproductive hormones. Changes in the levels of follicle-stimulating hormone, luteinizing hormone, and the hormone prolactin, can all impact ovulation.
One of these disorders is called primary ovarian insufficiency (previously called premature ovarian failure), which is when a woman’s ovaries stop functioning normally or become depleted before they reach 40 years old. It’s less common than PCOS, affecting 1 in 100 women younger than 40, and can also be caused by genetics or an autoimmune factor, according to The National Infertility Association.
Endometriosis is a condition where the tissue that lines the uterus starts to grow in other places, like the ovaries, behind the uterus, or in the fallopian tubes, causing irritation and the development of scar tissue (adhesions). Besides being extremely painful (though some women may experience no pain), it can make it very difficult to get pregnant by blocking the fallopian tubes, disrupting implantation, causing inflammation in the pelvis, and even altering egg quality, according to the American Society for Reproductive Medicine. Adhesions can also form after pelvic surgeries or trauma to the reproductive organs, such as dilation and curettage (D&C) during pregnancy termination or miscarriage, or a previous C-section.
Armando Hernandez-Rey, M.D., reproductive endocrinology & infertility doctor at Conceptions Florida, notes that trying to get pregnant earlier may help the chances of getting pregnant despite endometriosis. “A woman who [tries to get pregnant] at 23 and has even severe endometriosis won’t be as affected as someone who waits until 37 and then has the diagnosis,” he says. That’s because generally your eggs are higher quality, increasing the odds you’ll conceive despite the endometriosis.
While treatment varies from person to person, surgically removing the scar tissue can improve your chances of becoming pregnant especially when paired with fertility treatments such as IVF.
4. STIs, other infections, and growths in the reproductive system
Endometriosis is the most common physical change to the reproductive system that affects fertility. But other anatomical changes in the uterus, ovaries, and fallopian tubes can impact your ability to get pregnant.
The most likely of these is a blockage in the fallopian tubes. “Tubal infection is most likely caused by an organism that starts in the cervix and then goes up into fallopian tubes,” Uhler explains. The most common: gonorrhea and chlamydia. “If left untreated, [an infection] can cause scarring of the fallopian tubes. That’s where the egg and sperm meet, and they’re not able to if it’s blocked,” she says. Sometimes this blockage can be corrected surgically, but oftentimes, when the damage is extensive, fertility doctors will go straight to IVF since it just takes the tubes out of the whole process.
Other things that can decrease your chances of conceiving are uterine fibroids, polyps, and cysts.
5. Waiting to get pregnant
For many women, simply waiting to get pregnant is a huge contributor to infertility. Now, about 20 percent of women in the U.S. wait to have their first child until after age 35, according to the U.S. Department of Health and Human Services, making age a growing cause of fertility problems. In fact, about one-third of couples trying to conceive when the woman is over 35 have difficulties.
“The most important driver [of infertility] is egg quality,” Copperman says. “A woman is born with all the eggs she’s ever going to have in her lifetime. In general, in her 20s, 90 percent of her eggs are normal, and in general, in her 40s, 90 percent are abnormal,” he adds. Of course, there are exceptions, but this is the typical reproductive aging story. The longer you wait to get pregnant, the greater your chance of having abnormal or too few eggs to conceive.
Luckily, Copperman notes we live in a time where women are able to take better control of when they want to have kids. “I’m seeing more women freezing their eggs; there’s more awareness in reproductive aging than ever before.” More companies are including egg freezing in medical insurance plans, and gynos are encouraging younger women to think about family planning. “More and more women are freezing eggs, so when they’re 40 and want to have a baby, it’s easier.” And as long as a woman is in good health, there’s a better chance an egg frozen when she was younger will implant than a fresh egg when she is closer to menopause. “The uterus does not really appear to age,” Copperman adds, so as long as the egg is good, your uterus is ready to receive.
6. Unhealthy body weight
Having a BMI that’s too high or low has a proven impact on the ability to get pregnant. “Being overweight or obese, you can have a two- to four-fold higher risk of being unable to conceive, depending on type of obesity, and almost a six-fold risk of having miscarriages,” Hernandez-Rey explains. Being extremely over or underweight can impact the pituitary gland, causing it to malfunction and spark problems with ovulation.
In fact, according to the American Society for Reproductive Medicine, 12 percent of primary infertility results from deviations in body weight, meaning either obesity or low body weight. Luckily, it’s a cause of infertility that can typically be reversed. “Weight reduction definitely has positive effects and is positively correlated with good prognosis,” says Hernandez-Rey. If there’s no other contributing factor impeding fertility, over 70 percent of women who are infertile for this reason will be able to conceive without intervention once they’re at a healthy body weight.
7. Other unknown causes
The American Society for Reproductive Medicine says in about 5 to 10 percent of cases of couples having a tough time conceiving, all the fertility tests come back normal. This, or in cases where only minor abnormalities that wouldn’t result in infertility are found, is referred to as unexplained infertility. Uhler says that the course of treatment varies depending on the woman’s age—if she’s younger than 35, doctors will try simpler treatments like fertility drugs and artificial insemination; if she’s older and it seems appropriate, they may go straight to IVF.