The first trimester is the time when the fertilised ovum implants into the uterus and begins to develop. It lasts about six weeks, until about the 12th week of pregnancy, with 1-2 weeks for implantation and 10-11 menstrual cycles. The second trimester is from weeks 13 to 27 of pregnancy. This is the period where your baby’s brain, spine, muscles, heart and other organs form and grow. The third trimester starts about 28 weeks after conception (or 8 months) until birth.

Pregnancy usually lasts about 40 weeks from conception to birth. Conception is when a male sperm fertilizes a female egg and begins the process of creating a baby. The first 12 weeks of pregnancy are in the first trimester, weeks 13 to 27 are in the second trimester, and weeks 28 to 40 are in the third trimester.