Elena Scotti/FUSION

When we're teenagers, well-meaning teachers and mentors devote countless hours and awkward pamphlets to teaching girls how to avoid becoming pregnant—because, according to these early sex ed lessons, a baby is made the instant unprotected sex occurs.

If only that were true. As the millions of women who have struggled with infertility know, becoming pregnant often takes what feels like a religious miracle. Women are only able to conceive for a relatively small window of their adult life—and when a pregnancy doesn't occur after months or years of unprotected sex, they're often left wondering, "Why?"

Advertisement

Which is why women’s health advocates are starting to push for sex educators to offer a more realistic early education on how pregnancy actually works, and for doctors to talk to women about fertility before it’s too late for them to make truly empowered choices. This means explaining why ovulation, egg health, and age really matters before a woman decides she’s ready to have a baby.

While 20-somethings today may have missed out on learning the birds and bees of fertility in a high school class (I know I did), let the sexual re-education begin right now. Here's everything you need to know about making a baby that your doctors, teachers, and parents never told you.

1. Why egg cell count matters

While most of us are well aware of this ticking biological clock, we don't really know why it ticks. It comes down to a combination of egg count and egg age.

Advertisement

Women are born with about one to two million egg cells (oocytes) in our ovaries. By the time we hit puberty, it's down to 400,000. By age 50, most women run out of egg cells—and therefore eggs. This means that, if a woman wants to have a baby, she has to do so between puberty and 50.

During our lifetime, only a small percentage of egg cells will develop into actual eggs, released during the menstrual cycle. The rest degenerate.

2. Why egg age matters

As women age, their eggs are more likely to have chromosomal abnormalities, which can lead to miscarriage and birth defects. More specifically, at age 23, about one in two eggs will be normal, said Carolyn Givens, a reproductive endocrinologist at the Pacific Fertility Center in San Francisco. By age 35, it's down to one in five, she said and by age 40, it's one in ten.

Advertisement

This is why women who get pregnant later in life—their late 30s and 40s—are at a higher risk for miscarriage and babies born with Down syndrome. These abnormalities also make egg freezing and in-vitro fertilization (IVF) more complicated as women age. For example, a woman who goes through IVF may need to produce 10 eggs just to get one that is normal.

3. The truth about egg freezing

According to EggBanxx, a company that helps women finance elective egg freezing, the average age of their client is 35 to 37. Givens says the same about the patients at her clinic, and that these patients must freeze at least 20 mature eggs to have two children.

Advertisement

But doing so is easier said than done for many women. One round of egg freezing may only result in harvesting five to 10 eggs, and each round costs roughly $10,000 to $12,000.

When women freeze their eggs in their 20s (whether to become egg donors or preserve their fertility before going through chemotherapy), most not only produce more eggs per round, but more healthy eggs. "The ideal age to freeze eggs is age 19, or the early 20s, the younger the better," said Givens. "But I have yet to see a 20-something freeze her eggs in my clinic."

Of course, freezing your eggs is both invasive and prohibitively expensive for most, and a choice that should only be made after careful consideration. It's also not a guarantee of pregnancy.

4. Checking your ovarian reserve

Which brings us back to egg quantity. If you're intrigued by the concept of freezing your eggs and wondering if you might be a good candidate, you'll want to start by asking your doctor to evaluate your ovarian reserve—or roughly how many eggs you can harvest in a given cycle.

Advertisement

A test to check your ovarian reserve usually involves a vaginal ultrasound and blood tests to measure hormone levels, which must be conducted when a woman is menstruating. Women who are on birth control (and therefore not really ovulating) are told to go off birth control for several months before the test.

Between the ultrasound and blood tests, a doctor can determine how many eggs you might be able to grow in one round with the help of hormones. While a 21-year-old woman might grow 30 to 40 eggs in one round, by age 40, that number drops to six or eight eggs. The older you get, the harder it becomes to produce eggs.

Bear in mind that having a low ovarian reserve now does not necessarily predict your pregnancy chances for the future; it simply predicts how many eggs you can grow now. Some women may have a low ovarian reserve, but then conceive naturally.

Also, while these tests reveal egg quantity, they don't reveal egg quality.

5. Know your fertile window

What about those of you who want to start a family now? Above all, know that your menstrual cycle is key to pregnancy. Why? Again, pregnancy doesn't always happen when penis meets vagina.

Advertisement

A woman has a very specific "fertile window" that lasts about six days every month, during which she is most likely to conceive. "Only about 10 percent of women can identify successfully when their fertile window is," said Kirsten Karchmer, founder and CEO of the fertility tracking app Conceivable, which includes ovulation tracking.

Fertility apps (of which there are now several) all focus on ovulation because this window occurs around ovulation—that magical time when an ovary releases an egg into the fallopian tube to await fertilization, where it sits for about 24 hours. The window lasts six days because sperm can survive for up to five days, thus you can get pregnant days after having sex.

If the egg is not fertilized during that window, your cycle continues, your uterine lining is eventually shed, and voila—a period occurs.

Advertisement

Knowing your fertile window (which can be done by keeping track of your period, monitoring basal body temperature, and evaluating cervical mucus) can help women figure out when they should be having sex to actually make a baby. "When women are actively tracking their cycles they have a 40 percent greater chance of conceiving," Jennifer Tye, a spokeswoman for the fertility tracking app Glow, told Fusion, referring to the app's success rate.

5. The power of planning ahead

Even if you're not ready to have a baby, now is the time to educate yourself about your fertility, whether this includes planning ahead before you start "trying" or saving up to freeze your eggs. If you want to have a baby at 32, don't start thinking about it at 32. That way, if faced with obstacles, you won't lose valuable time.

Advertisement

To put this in perspective, I recently attended one of EggBanxx's educational sessions in Los Angeles. During the talk, a 44-year-old woman raised her hand and asked the doctor on stage, "Why didn't anyone teach us this earlier?" He responded, "They should have." He then told her the odds of having a baby at 44 with IVF were practically one in a million.

Taryn Hillin is Fusion's love and sex writer, with a large focus on the science of relationships. She also loves dogs, Bourbon barrel-aged beers and popcorn — not necessarily in that order.