What typically signifies the end of the first trimester during pregnancy?

The end of the first trimester in pregnancy is typically marked by the completion of 12 weeks gestation. This time frame corresponds to the notable developmental milestones of the embryo and the early progression of pregnancy. By the end of the 12th week, the embryo has transitioned into a fetus, and most of the critical organ systems have formed.

This developmental stage is significant because it coincides with a reduced risk of miscarriage and allows for many women to move confidently into the second trimester.

While other options such as the first ultrasound, the detection of fetal heart sounds, and the first movements felt by the mother are important events in a pregnancy, they do not specifically denote the end of the first trimester. The first ultrasound can occur at various weeks; typically, it may happen around 7 to 10 weeks for dating purposes. The fetal heart sounds can be detected as early as 6 weeks, but the mother might not perceive them until later. Finally, the mother typically feels fetal movements around 18 to 24 weeks, which is well beyond the first trimester.