In the second trimester around weeks 13-17, which feature becomes evident?

• A. Heart valves mature
• B. Fingerprints form
• C. Lungs fully functional
• D. Neural tube closes

Answer: (B)

Between weeks 13 and 17, visible external features begin to emerge as the fetus continues to develop. Fingerprints form during this period because the skin on the fingertips develops epidermal ridges that create unique patterns. These ridges start forming earlier but become evident in this window, so fingerprints are the observable feature most likely to be noted then. Other options describe processes that occur earlier in pregnancy or aren’t yet fully developed by this time—for example, the heart’s valve formation is largely established earlier, the lungs aren’t fully functional until after birth, and neural tube closure happens far earlier in gestation.