Pregnancy usually lasts 280 days or 40 weeks, which is contracted from the first day of the last menstrual period starts. This period can be divided into three "trimester" of pregnancy divided in any specific events occur the first trimester of pregnancy to the end of the first week, 13 weeks, 14 weeks up to the 27th week of the second quarter, and quarter the third weekend of 28 to 40 weeks is mostly at this time (earlier or later) leads to labor and birth.