The usual menstrual cycle lasts around 28 days. This implies that between the first day of your period and the first day of your next period, around 28 days pass. This textbook cycle, however, does not apply to everyone. You may notice that your periods occur every 21 to 35 days. This is called "anovulatory cycles." Most women who experience anovulatory cycles also have fewer than 12 menses over a three-month period. As long as there are no more than two gaps of at least seven days in a row, this is not considered significant. Your doctor will be able to tell you how frequently you are likely to get pregnant if you express breast milk after your period has come out. If you are planning a pregnancy, then it is important to wait at least six months after your last period before trying for babies. If you do become pregnant during those six months, then the baby will be born alive but will not survive for more than a few weeks without intervention. After six months, the risk of serious complications arising from pregnancy goes up significantly; therefore, it is important to take measures to avoid getting pregnant after this time. It is important to remember that fertility peaks at different times for men and women. Men can produce children well into their 70's and 80's while women's fertility declines after about 40 years of age.