Weeks 1–12 of your pregnancy: an overview of what to expect? In general, the average pregnancy lasts for about 40 weeks, of which the first trimester is also known as the "earliest phase of pregnancy," starting on the first day of your last period. For every woman, pregnancy is different. Source: https://www.drelsa.net/blogs/weeks-112-of-your-pregnancy-an-overview-of-what-to-expect