Your plan, your way.

Fertility is the ability to produce a child, essentially. For women, it’s producing fertile eggs. For men, fertility means having sperm that can fertilize an egg. Age, genetics, environment, lifestyle, and a variety of other things impact fertility — but we’ll get into all of that!

It looks a little like this: first, the ovaries contain many egg cells, called ova or oocytes. After ovulation, one of these oocytes is transported to the fallopian tube where fertilization by a sperm can occur. The fertilized egg then travels to the uterus, where it can implant into the thickened uterine lining (the endometrium) and continue to develop. If fertilization doesn’t happen, the uterine lining is shed as menstrual flow. The female reproductive system produces female sex hormones — estrogen and, later, progesterone — that maintain the reproductive cycle.

Ovulation is when an egg is matured and released from the ovary, pushed down the fallopian tube, and made available to be fertilized. It’s preceded by a surge of the hormone LH, which can often be detected with a urine ovulation predictor kit. The day of ovulation is your most fertile window, but you can potentially conceive from unprotected sex anywhere from 3 days before to 3 days after. The first part of the cycle is the follicular phase; the second, from ovulation until the next period, is the luteal phase. Cycle-tracking apps make this easy — though they’re less helpful if your period is irregular.

For women who know they want children — or want the option — it’s never too early to start understanding your fertile health. If you’re not planning to have children until your 30s, our doctors advise getting a fertility assessment as early as your late 20s.

Everyone is a little different, but a rule of thumb looks like this: at puberty you have around 300,000–500,000 eggs remaining; at 37, around 25,000; and at 51 — the average age of menopause in the U.S. — around 1,000. (Source: American College of Obstetricians and Gynecologists.)

Ovarian reserve describes the ovary’s ability to provide egg cells capable of fertilization. A woman is born with all the eggs she’ll ever have, and the reserve decreases with age: roughly 20–40% remains during peak reproductive years (18–26), a little over 10% at age 30, and only about 3% at age 40. (Source: “Human Ovarian Reserve from Conception to the Menopause,” PLOS One.)

The main complication of endometriosis is impaired fertility — it affects approximately one-third to one-half of women with the condition. If you have or suspect endometriosis, an early conversation with a fertility specialist can make a real difference in keeping your options open.