Understanding Fertility Cycles

For many women, the menstrual cycle is something you can have your entire life, without understanding the science behind it. Sure, the practical aspects you know, like when to stock up on the Tampax and ibuprofen, but exactly what your cycle says about your ability to conceive a child might be a bit of a mystery. When you want to start a family or add to your current one, though, it’s important to understand how your cycle works and when you’re most likely to be fertile.

Period Basics

When you begin reading literature about pregnancy, the first thing you’ll notice is that it will often reference “day X” of your period. For example, “Days 11-16 of your period are when you’re most likely to be ovulating.” These days are measured from the first day of your period, and often assume a 28 day cycle.

The changes in your ovaries and uterus are responsible for the changes in your body throughout your cycle. These two parts of your female reproductive system work together to make you fertile. Your ovaries are the organs that store your eggs and release them down into your uterus, where they can potentially be fertilized by your partner’s sperm.

Your uterus, a.k.a. your womb, is the area directly above your vagina, and it goes through its own monthly cycles, too. The uterine lining builds up and prepares for the egg, but this lining is sloughed off after ovulation, resulting in your period.

Ovulation & When You’re Fertile

In order to become pregnant, you’ll need an egg in your uterus, along with a successful sperm. The time during your cycle when the egg drops from your ovaries down to your uterus is called ovulation. In the average woman, ovulation occurs around day 14 of the cycle; the egg can live in the uterus for about 24 hours.

Although the egg can only survive a day, you’re actually fertile for about five or six days. This is because sperm can survive in the uterus for up to five days. Your fertile days are five days before ovulation, and the day afterwards. For about 50% of women, this will be days 9-15 of their period.

Predicting Ovulation

You’ll notice that predicting your days of ovulation might be more difficult if you’re not one of the 12% of women who has a 28 day cycle, or if you’re not one of the 50% of women who follows the “average” days of ovulation. Or even if you do have a normal cycle, you might want to increase your chances of pregnancy by being more certain about when you’re ovulating.

There are several at-home methods that are highly accurate at tracking your fertility. One, examining your cervical fluid, doesn’t require any equipment or special knowledge. You can also monitor your basal body temperature, or purchase fertility monitors or kits.

Sources:

The Menstrual Cycle and Ovulation. (2008) University of Cincinnati.

Menstrual Cycle & Fertility. (2011) University of California Davis.

Identifying Your Fertile Days. (2008) University of Maryland Medical Center.