Now, more than ever, women are delaying having children until later in life. According to the CDC, the average age a woman has her first child is 26. Why has the average age creeped higher? One reason is that fewer women are having children in their teens. The CDC notes that the rate of teen births has gone down 42% from 2000 to 2014. Another factor is that more women than ever are giving birth to their first child when they are over age 30. Women having their first child between the ages of 30 and 34 rose by 28% and women giving birth over age 35 rose by 23%. In cities the average ages are even older. In Manhattan, for example, the average age a woman has her first child is 32, according to the New York Times.

The reason why women are waiting longer to have children is complex. The pursuit of higher education and career goals is often cited in the media as a factor influencing women to wait until they are older to have their first child. Forbes noted that in a survey of thousands of women, money was a leading reason why women are waiting to have children. According to the Atlantic writer Jean M. Twenge, in an informal survey of successful professional women, 42 percent of women had not had a child by age 40. But this is of course not the only factor. Higher student loan debt, economic insecurity, and the choice to “settle down” later also play a role. Culturally, women have other priorities beyond raising children, such as the pursuit of personal goals, self-development, hobbies, volunteering, and other pursuits. Some women wait until later in life to get married, and others don’t want to get married at all. However, some women, as they approach 40 find themselves reaching a crucial milestone where a decision must finally be made–to have children or not to have children.

We know that a woman’s fertility declines as she ages. The American Society of Reproductive Medicine notes that women’s fertility begins to decline at age 32. It is scientifically understood that a woman’s peak reproductive years are in her 20s. And yet, these peak years also coincide with the optimal age for other pursuits. Women have been told that waiting later to have children can come at the price of fertility difficulties later in life. But recent research indicates that waiting until your late thirties may only decrease your fertility by a few percentage points. Even women who wait until their 40s can see good outcomes. According to the New York Times, more than 100,000 women in their 40s give birth to healthy babies every year. While we know a woman’s fertility declines in her 40s, this area of female fertility has been studied very little, and most of the information we do have comes from I.V.F. statistics which have very little to do with the chances of having a baby naturally.

In order to fully understand what it means to have a child in your 40s, we need to first understand a few things. In this article we will take a closer look at these factors, namely:

• The truth about fertility in your thirties.
• Why fertility declines in a woman’s forties, and what we know (and don’t know) about menopause.
• And finally, risk factors facing women when they get pregnant in their 40s.

Let’s first look at the information we do have for women’s fertility in the late thirties (that is between the ages of 35 and 40), because this research is very important when it comes to understanding fertility in your early 40s.

When a woman is born, she has about 1 to 2 million eggs in her ovaries. By puberty, this number has been reduced to about half a million. And by age 37, a woman will have about 25,000 eggs left. This sounds like quite a bit, given that women only release one egg a cycle, but each cycle results in the loss of more than one egg, and egg quality can decrease as a woman ages.

Does this mean that women should plan to have children in their 20s, even when it could potentially conflict with career and financial life plans? Is waiting until your 30s risky? And what about your early 40s? 

Jean M. Twenge, in her excellent article “How Long Can You Wait to Have a Baby,” does a great job dispelling some myths. For example, there is a “widely cited statistic that one in three women ages 35 to 39 will not get pregnant after a year of trying.” However, this statistic becomes questionable when we look at its source. Twenge notes that the source research is drawn from French birth rates between 1670 and 1830. It is important to interrogate these statistics because modern medicine offers women a range of options that can help them improve their chances of conceiving—everything from reliable ovarian monitoring systems, advanced medical care (for those with access to it), as well as I.V.F. and I.U.I. among other infertility treatments. Twenge claims that these alarming statistics have harmed some women. “We’ve rearranged our lives, worried endlessly, and foregone countless career opportunities based on a few statistics about women who resided in thatched-roof huts and never saw a lightbulb.”

Another reason why women in their late 30s may be concerned about their fertility might have something to do with I.V.F. statistics shaping the dialogue. (The Society for Assisted Reproductive Technology notes that a woman under age 35 has a 42.6% chance of success with I.V.F., while a woman between the ages of 38-40 has 19.7% chance of success. The chance of success declines significantly in the 40s. Women between the ages of 41 and 42 only have a 9.7% chance of success). A woman seeking I.V.F. in her late 30s has less chance of success with I.V.F. than a woman under age 35, but I.V.F. success relies on harvesting many eggs from the ovaries using hormones and surgery, something which cannot be compared to the process of producing one egg for natural conception. The key takeaway is this, the statistical decrease in fertility we see in I.V.F. statistics does not translate to the statistics for fertility with women trying to conceive naturally.

Another myth may have been propagated as a result of a “simplification” made by the American Society for Reproductive Medicine. The American Society for Reproductive Medicine notes: “A healthy 30-year-old woman has about a 20% chance of getting pregnant each month. But by age 40, her chance drops to only a 5% chance of getting pregnant in a given month.” However, Twenge didn’t see these statistics reflected in the scientific literature on female fertility and the ASRM noted that the numbers were “simplified for a popular audience, and did not provide a specific citation.” More recent research however, tells a more specific story than the one told by the ASRM.

Various studies have been conducted to look more closely at a woman’s chances of getting pregnant in her 30s. According to the journal BMJ, after one year of trying to get pregnant 60% of women between the ages of 35-39 will conceive, and 85% will be pregnant after two years of trying. This indicates that women who fail to conceive after one year (and are considered infertile) could still see pregnancy success if they don’t give up. The writers note that conception chances are highest in the first month. In the early months of trying, the chance of getting pregnant each cycle is 30%, but chances fall to 5% each month if the couple has been trying for a year. The statistics likely reflect the fact that women who have been trying longer and who have failed to conceive are likely less fertile than the women who get pregnant in the early months of trying.

Writers for the journal of Fertility and Sterility noted that the chance of pregnancy per cycle of trying among women in the 38-39 year-old age group was 13.2%, declining to 6.6% in the 42-44 year-old age group. This is assuming that the average pregnancy rate per cycle among women in their peak fertility years is 20% per cycle. The chances of pregnancy per cycle then, for women in their late 30s is only about half that a woman at her fertile peak.

Another study published in Fertility and Sterility found that women between the ages of 35 and 40 saw a 78% success rate of getting pregnant with timed intercourse. And the study found that overall, a woman’s age in her 30s had little effect on success.

Perhaps another way to look at this is to look at the women who fail to conceive after trying for one year. According to a study published in the journal of Obstetrics and Gynecology, if you look at the number of women who fail to conceive after trying for one year, age seems to make little difference. Among the 27 to 34 year-olds, about 13 to 14% of women will have failed to conceive after trying for one year. Among the 35 to 39 year-olds 18% will have failed to conceive after one year.

Can healthy women of average weight reliably count on their fertility up until age 40? Research seems to suggest the answer is yes. According to the journal of Fertility and Sterility 83% of women between the ages of 35 and 39 were pregnant within a year with timed intercourse or with having intercourse twice a week. According to the researchers, a woman at age 40 is about half as fertile as she was at 30, but her fertility isn’t zero.

Usually this difference can be overcome simply by timing sex more closely to ovulation, using fertility monitoring, making a conscientious effort to have unprotected sex at least twice a week, and ideally at different times during the week, eating healthily, and taking proper wellness supplements to prepare the body for pregnancy. Many women who are trying to conceive at younger ages are also wise to take these steps.

In fact, the average decline in fertility between a woman in her late 20s versus her late 30s may only be a few percentage points. More women are confidently having children well into their late 30s.

But what about having children in your early 40s?

What happens at around age 40 that leads to a more significant decline in fertility?

The big shift that happens in a woman’s 40s is that she enters menopause, usually in her late 40s. The National Library of Medicine defines menopause as the time in a woman’s life when her period stops, usually around age 45. This sounds simple and straightforward enough, but in order to understand what menopause means for your reproductive capacity, it is important to look more closely, because menopause is not a single event, but a series of events. Looking for the symptoms of menopause isn’t enough to signal significant decreases in fertility because a woman can be in the early stage of menopause and be symptom-free.

Menopause refers to the stage in a woman’s life where the ovaries no longer release eggs, where the monthly period stops, and where a woman is no longer able to have children. While many people often think of menopause as a single event, menopause is actually the culmination of a many years-long process (it can last up to a decade) where a woman’s fertility decreases, and eventually ceases altogether. In fact, a woman won’t be classified as post-menopausal until she hasn’t had her period for a full year. Sherry Sherman writes about the vague boundaries of menopause and the medical difficulties of defining menopause in her excellent American Journal of Medicine article, “Defining the menopausal transition.” She notes that even when a woman goes 12 full months without a period and is considered menopausal, there is anywhere between a 4% and 10% chance she could have another period, therefore extending the “pre-menopausal” or “perimenopausal” stage.

Because this stage is not a single event, but a period of time where a woman goes from being considered fertile to being infertile, some researchers call it the climacteric. Before this occurs, a woman’s period may be irregular, and it is also the time when she may experience symptoms associated with menopause—this is known as the menopausal transition. These symptoms can vary, but can include:

• Change in periods: shorter, longer, heavier, or changes in the time between each period
• Hot flashes
• Night sweats
• Trouble sleeping
• Vaginal dryness
• Mood swings
• Trouble concentrating
• Loss of hair on head

Rather than thinking of menopause as a single event, it can be helpful to think about menopause as the natural process of aging. A woman’s reproductive system undergoes many transitions and changes throughout her life, from her first period to the last. The process that unfolds in-between these two milestones is not as well understood. The World Health Organization created more specific terminology to describe the process leading up to menopause as “perimenopause,” and the process following menopause as “post-menopause.” But, as Sherry Sherman writes in the American Journal of Medicine, “There has been a growing awareness that progress in the research of reproductive aging and menopause has been impacted by the lack of meaningful, reliable, and objective criteria for designating menopause-related status in women participating in observational studies and clinical trials.”

If researchers and doctors don’t have a clear language for menopause and the aging process that leads up to it, how can they possibly discuss the process clearly with their patients? The authors note: “Specifically, contemporary terminology lacks the sensitivity and specificity needed to operationally define a woman’s reproductive status in the continuum of reproductive aging.” In other words, researchers have yet to invest significant resources in studying a process that involves up to ten years of a woman’s life and affects virtually every aspect of her health from hormonal changes, mood, and disease risk factors to her ability to have a baby. The symptoms a woman can experience in the period leading up to menopause include “hot flashes, night sweats, uterine bleeding problems, and vulvovaginal atrophy. Mood changes, sleep disturbances, and sexual dysfunction are also commonly reported.” Other health conditions include increased bone loss after menopause.

Sherman writes that the terminology could be clarified further if we referred to a woman’s reproductive lifespan in terms of a reproductive period which includes her early, peak, and late period, followed by an early and late menopausal transition period, followed by post-menopause (at which point she is no longer fertile). Where age fits in varies from woman to woman. Cleveland Clinic notes that some women will enter the early menopausal transition in her late 30s and early 40s while others will enter the transition in the late 40s. Furthermore, the transition between her late reproductive period and her early menopausal transition period is not a moment in time, but a slow and unfolding process. In other words, fertility is not an alarm bell that rings when you turn 40. It’s more like an hour-glass of sand. You have less and less of it, until you have none left.

Saying that menopause happens at 45 is a safe median estimate when you take all women into account, but it says nothing about what your experience might be. You very well could be fertile well into your 40s, or you might not. Family history of onset of menopause might offer a clue about where you might stand, but again, it won’t necessarily tell you when you’ll no longer be fertile.

Are there reliable tests to determine whether a woman is in the first stages of menopause? Unfortunately, no. While fertility doctors can perform tests to determine ovarian reserve, these tests are only helpful for doctors in determining who might be a good candidate for I.V.F. success and not whether a woman can and cannot conceive naturally. And even in the field of ART, these tests are up for debate. According to Rachel Gurevich, writing for Very Well Family, an FSH level considered too high for I.V.F. will vary from clinic to clinic and doctor to doctor. For example, high levels of FSH on a day three FSH test have been correlated to lower ovarian reserves. But it is important to note that FSH levels will be elevated in both the late reproductive period and early menopausal transition period. And women who are infertile due to age can still show normal FSH results.

What’s the takeaway? There’s no test out there that can tell you that it’s too late to have a baby. The only reliable marker that your fertile period has ended is menopause, that is, you haven’t had your period for a year. You can’t just go to the doctor and test for menopause. When it comes to family planning, having a baby during your peak reproductive years (when you are under age 35) will require the fewest interventions. When it comes to having a baby after age 35, women may need to time sex to their fertile window (to overcome declining fertility) and be diligent about nutrition, their health, and prenatal care. Given that the transition to menopause is gradual, the average healthy woman trying to have a baby naturally in her early 40s may be more similar to a healthy woman trying to have a baby in her late 30s, but it is important to note that this age group has been poorly studied outside the context of assisted reproductive technology. Jean M. Twenge in her article for the Atlantic concluded that women should aim to try to have their last baby before 40, because after 40 there is little research about women’s chances of success. There is also an increased risk of pregnancy complications that women who have a baby in their early 40s face. Let’s take a closer look.

Women who are pregnant in their 40s face additional pregnancy risks than younger women. What are the risk factors when you get pregnant in your 40s? They include:

• Higher risk of miscarriage. BMJ notes that the risk of miscarriage was 53% in women aged 45 or above. The New York Times notes that women between the ages of 40 and 44 have a risk of miscarriage of about 33%. Many miscarriages occur early in a pregnancy. This is usually due to chromosomal abnormalities in the fetus. However, it is also important to note that miscarriage is a risk factor in every pregnancy. Even younger women can have miscarriages. Among women in their prime fertility years, 10% of pregnancies end in miscarriage.
• Complications. Women in their 40s are at greater risk of pregnancy complications like preeclampsia, gestational diabetes, low or high birth weights, placenta previa (a condition where the placenta covers the cervix) and premature delivery. According to the journal Geburtshilfe und Frauenheilkunde older women are more likely to suffer from chronic medical conditions that need management during pregnancy.
• Risks to the Baby. Chromosomal abnormalities are a risk in all pregnancies, but some chromosomal abnormality risks are higher in older women. For example, according to a New York Times article about the risks of giving birth after 40, the risk of giving birth to a baby with Down Syndrome is 1 in 100 after age 40. At age 25 the risk is only one in 1250. As a woman ages, the quality of her remaining eggs decreases. The chance that she’ll release an egg with chromosomal abnormalities increases. There are tests available that women can take to determine the fetus’s risk.
• Pregnancy Plans. Being over 40 could affect your pregnancy plans. Women over 40 were four times more likely to have a caesarian and were more likely to require longer hospital stays.

This can all sound alarming, but the writers in the journal Geburtshilfe und Frauenheilkunde noted that pregnancy outcomes were good for women over 40 when pre-existing medical conditions were properly monitored or treated with medicine or diet. Women who followed their doctors’ instructions regarding prenatal care, those who made healthy lifestyle choices, and who delivered their babies in a perinatal center saw good outcomes. The writers note: “the majority of pregnancies of older mothers turn out to be uncomplicated.” The NYU program director at the Langone Fertility Center at NYU was quoted in the New York Times noting that his patients (whose average age was 39) “do quite well.”

If you can plan to have your children before you reach 40, most experts will say you should. If you can plan to have your children before age 35, this is even better. However, some women reach the milestone age of 40 and still haven’t had children for a range of reasons. For some women this moment in their lives becomes a key turning point, where a decision must be made.

The key takeaways are this. If you have reached 40 and have never tried to have children but want to try now, the good news is that many women each year succeed in delivering healthy babies in their 40s, and especially in their early 40s. However, women who embark on their pregnancy journeys in their 40s face unique challenges. Declining fertility may mean that getting pregnant naturally may no longer be possible. If you learn that you need fertility treatment, the chances of success are far lower when you are over 40 and you may want to work with a doctor or clinic that specializes in treatment for older women. If you do get pregnant, the chances of miscarriage and other complications are higher, so following through diligently in your prenatal care and following doctor’s instructions is essential.

Finally, it can be helpful to think of the benefits of being an older mother. Older mothers are often more settled financially and in their careers. They have often lived full lives before bringing children into them. They are more likely to do their research to ensure their pregnancies are healthy. They are more likely to eat well, take wellness supplements to promote prenatal health, and are more likely to have the wisdom of their years that younger mothers may not have. Waiting a little later to have children can result in many couples (and single mothers) building beautiful strong families. That said, a woman may be wise to speak to her doctor about potential risks if she plans to try to become pregnant after 40. Proper planning and thought can lead to better outcomes.