By the end of the first trimester, the fetus is about the size of a plum and has what percent of adult organs?

• A. 30%
• B. 60%
• C. 90%
• D. 100%

Answer: (C)

By the end of the first trimester, the major organ systems have formed and begin to function, and the fetus is about the size of a plum. At this point those organs have reached roughly ninety percent of their final adult size, with further growth and maturation continuing mainly in the later trimesters. The lungs and some other systems continue to mature after birth, so full maturity isn’t reached yet. So the best answer reflects that most organs are already well formed and approaching their adult size, around ninety percent. The lower percentages would underestimate how far development has progressed, while a hundred percent would imply full maturity too early.