The first menstruation after pregnancy may be rather abnormal, as your body has not had a period for nearly a year. Note that most women do not experience postpartum menstruation for several weeks, or even months, after the birth of their baby. In fact, the average woman sees the return of her period anywhere from six to eight weeks postpartum, though women who choose to breastfeed may not get a period until they wean their baby. Of course, you can expect to bleed for up to six weeks after childbirth, but this is called lochia, and is not considered menstruation. When you finally get your period, it will likely be somewhat heavy at first, and may also last longer than usual, but it should gradually return to the way it was before pregnancy.
It may be difficult to distinguish the postpartum lochia from the postpartum menstruation, but you should know that the former usually starts immediately after childbirth. It can continue for up to six weeks, but most women find that it tapers off closer to three or four weeks postpartum. Most women do not get their first menstruation after pregnancy until they are at least six weeks postpartum, so you will likely experience a break of a few weeks between the two instances of bleeding. On the other hand, if your lochia seems to increase after a few weeks rather than gradually slowing down, you should see a doctor, as this may indicate either an early period or a postpartum complication.
Once you are sure that it is indeed your period that you are experiencing, you should be prepared for an unusually heavy flow. This is typically because the body has not had a period in so long. In fact, the first menstruation after pregnancy tends to last longer than the usual period, as well, so be prepared with extra tampons or pads. You may be relieved to know that just because your first postpartum period is heavier does not mean that it will always be this way. In fact, many women find that the subsequent periods are lighter than usual, though after several cycles, they eventually balance out.
Just like there is little way to pinpoint when your first menstruation after pregnancy will occur, it is also hard to tell when the subsequent periods will show up. This is because most women find that the time between periods can vary after childbirth. You may get a heavy period, and then experience no bleeding for a couple of months. Similar to the flow, however, the regularity of the periods should eventually balance out. Of course, if you are sexually active during this time, a period that suddenly goes missing may indicate the need for a pregnancy test.