If you are pregnant, but have not yet started experiencing morning sickness, you might want to know when it's supposed to start. According to the American Pregnancy Association, morning sickness will usually rear it's ugly head around 6 weeks of pregnancy, and ends around 12 weeks. It's important to note though that this is not always the case, because some women (myself included) experience hyperemesis gravidarum, which is an extreme version of "morning sickness" that can last the entire pregnancy.