Though your 20s may be the best time to get pregnant biologically, many people are waiting until their late 30s or 40s to start a family. Here’s how fertility changes as you age.

Females are born with all the immature egg follicles they’ll ever have — about 1 to 2 million. But only about 300,000 to 500,00 of those eggs remain at the start of menstruation, around age 12.

With each period, several hundred eggs are lost. Only the healthiest follicles will become mature eggs. The body breaks down and absorbs the rest. Males, on the other hand, continue to create new sperm for most of their adult lives.

As the body ages, it has fewer follicles, which means the follicles have fewer opportunities to create healthy, strong eggs for fertilization.

The supply is robust in the teenage years, but by the late 30s and 40s, there are significantly fewer, with an average of 25,000 by age 37. However, that’s the age when more and more people are attempting to start a family.

Today, the average age of giving birth for the first time is 27.5 years. That age has been steadily increasing in recent years as parenthood is postponed.

Let’s take a look at how the decision to wait can affect your fertility.

If ever there was a “best” age to procreate purely from a physical standpoint, this would be it.

Your body’s strongest ovarian follicles are the first to mature into eggs for ovulation, so the eggs you produce in your younger years are more likely to be high quality.

Having a child at this age will reduce the risk of:

  • birth defects
  • chromosomal problems
  • some fertility issues

Of course, pregnancy at this age is not entirely without risk.

This fertility chance, also known as the fecundity rate, will wax and wane through your life. It’s at its strongest in this younger age period. By age 30, the natural fertility rate each month is about 20%.

Overall, fertility rates have dropped over the last several decades for females ages 18 to 24 but increased slightly for those in their 30s and 40s as many are choosing to wait until their older to start families.

With each passing year, your chance of naturally conceiving falls. But in your late 20s, your chance of getting pregnant without intervention remains fairly steady.

In fact, couples under age 30 who are otherwise healthy are able to conceive in their first 3 months of trying 40% to 60% of the time. Your body still has a generous supply of eggs to provide during these years.

But if you’re trying to conceive and have been unsuccessful for at least 3 months, talk with your doctor. While most couples at this age will be able to have a baby without intervention, some guidance may be helpful.

In your early 30s, the chances you’ll be able to have a baby are still high, and you still have many high quality eggs, but your odds will start to decline steadily at this age. In your 30s, you’re about half as fertile as you are in your early 20s.

Does that mean you can’t have children if you’re in your 30s? Absolutely not.

In fact, 1 in 5 females nationwide have their first child after age 35, notes the National Institutes of Health. However, infertility issues are more common than in your 20s.

Though statistics differ, they all agree that it’s harder to get pregnant during these years.

By age 40, a woman’s chance of getting pregnant is less than 5% per cycle, according to the American Society for Reproductive Medicine.

But according to the American College of Obstetricians and Gynecologists (ACOG), a woman who is 40 has around a 10% chance of getting pregnant per menstrual cycle.

This fall in fertility rates happens to coincide with the decade of life when more people than ever are trying to get pregnant. However, at this age, the risks of chromosomal issues with eggs are higher. The risks increase with every additional year. That means the risks of miscarriage or abnormal pregnancy are higher.

The fastest-growing rates of childbearing are in females 40 and older due to people choosing to start families later in life. However, while more individuals are giving birth in their late 30s and early 40s, the overall percentage of births to older parents is still much lower than in younger ones because it’s harder to get pregnant if you’re over 40.

By this age, your body is preparing for menopause. Your ovaries have likely exhausted their follicles or are nearing the end of their supply. With each passing cycle, more will disappear. By the time you reach your early 50s, you’ll have almost no follicles remaining.

Babies born to parents in this age range are also at greater risk for a number of birth irregularities and pregnancy complications. Miscarriage and chromosomal abnormalities increase significantly during this period of life.

A 2019 population-based study from Norway found that the risk of pregnancy loss is 53% in women over 45, compared with 10% in women ages 25 to 29.

Older age also increases the risk of complications for the parent, including:

  • diabetes
  • hypertension
  • preeclampsia

Today, people are waiting longer to start families. Because of advancements in fertility treatments, such as in vitro fertilization, these individuals often do succeed at getting pregnant at this later stage.

While your natural window gradually closes with age, fertility treatments may be able to extend your window and even make your chances of successful conception higher.