A woman is most fertile around one to two days before ovulation (when the egg is released from the ovary). Ovulation occurs on different days for different women and can vary month to month for many women; some women can have longer or shorter cycles. Ovulation typically happens 11 to 21 days into a menstrual cycle.

Hormones are responsible for sending the messages that lead to the development of mature eggs and trigger ovulation. Ovulation can be delayed if stress, illness, or a significant disruption of a woman’s normal routine (such as sleep deprivation) interfere with the production of those hormones.

A basal body temperature (BBT) chart can indicate that a woman has ovulated and provide additional useful information, but it does not predict ovulation. Ovulation predictor kits, however, detect the presence of the hormone that triggers ovulation and can help predict the days a woman might be most fertile.

There’s no reason to wait to try to get pregnant after discontinuing birth control pills. Most women start ovulating again about two weeks after taking the last pill.

On average, sperm can survive inside a woman’s body for three to five days.

Research indicates that it isn’t necessary to have intercourse every day during the fertile window to conceive; every other day or every third day can work just as well.

There’s no scientific evidence that a specific position during intercourse can enhance or decrease the chance of the sperm reaching the egg, and you can get pregnant having intercourse in practically any position. However, some doctors consider the missionary position (man on top) optimal for conception.

Partners aged 29 to 33 who have normally functioning reproductive systems have a 20% to 25% chance of conceiving during any given menstrual cycle.

After six months of trying to conceive, 60% of couples in which both partners are 29 to 33 and have normally functioning reproductive systems succeed. In general, about 90% of couples will conceive within 12 months.

Infertility is the inability to conceive after 12 months of regular unprotected intercourse.

Among couples who are of childbearing age, about one in eight have been diagnosed with infertility. More than 7.3 million people in the U.S. are affected.

About one-third of infertility cases are caused by male factors (such as low sperm count or malformed sperm), and about the same percentage is caused by female factors (such as ovulation issues or blocked fallopian tubes). About one-fifth of infertility cases are unexplained, and the remaining cases are caused by a combination of problems in both partners.

Smoking may reduce a man’s ability to produce healthy sperm and can be harmful to a woman’s ovaries, accelerating the loss of eggs.

If the woman is 35 or older, an infertility diagnosis is considered after only six months of regular unprotected intercourse. A woman’s chances of having a baby rapidly decrease every year after age 30. As a woman ages, she has fewer healthy eggs remaining, her ovaries become less able to release eggs, and she is more likely to have health conditions that can lead to fertility problems.

About 20% of American women have their first child after age 35. Approximately one-third of couples in which the woman is at least 35 experience fertility issues.