What significant change occurs to the baby's size during the second trimester?

During the second trimester, one of the most notable developments in fetal growth is the significant increase in size, particularly in length. By the end of this period, the fetus can reach approximately 20 inches, marking a notable doubling from its size earlier in the pregnancy. This growth is crucial as the fetus continues to develop its musculature, organs, and overall physiological systems.

The second trimester is characterized not just by growth in length but also by the continued development of bodily systems. While the earlier stages of pregnancy focus on establishing the basic anatomical structures, the second trimester sees substantial maturation and growth, laying the groundwork for a healthy fetus.

Other options provided focus on movement, positioning, or changes in the mother's body, which, while relevant aspects of pregnancy, do not capture the key developmental milestone related to the baby's size that is characteristic of this trimester.