You may notice the timing and volume of your period differs. Your menstrual cycle can be affected by stress as well as by medical conditions, such as an overactive thyroid. In both these cases, periods can become lighter or less frequent. If your periods are erratic, it can be difficult to predict when you might ovulate. Unpredictable or missed periods may mean that ovulation isn't occurring at all. If you know this to be the case because you're monitoring the signs of ovulation (see Are you ovulating?), or using ovulation predictor tests (see This is Day 8 of your Menstrual Cycle), seek medical advice about your fertility.

You may be able to become pregnant naturally and easily despite problems related to your period, but some conditions that cause long, irregular, or heavy periods are linked to lower fertility. Heavy periods can be caused by conditions such as fibroids, which can affect fertility. A higher than average level of blood loss can also make you anemic, which is not the best start for pregnancy for you or your baby, so you may want to look at boosting your iron intake.

Painful periods can impact fertility. Endometriosis is a common disorder that can make periods painful and cause discomfort during sex. If you have these symptoms, see your doctor who might arrange a scan or refer you to a specialist. In endometriosis, cells resembling those that line the uterus come to lie outside the uterus on structures such as the ovaries, the fallopian tubes, and walls of the pelvis. There are treatments for endometriosis, including laser surgery, that can boost a woman's chances of conceiving.