Hint: Pregnancy
The answer to this puzzle is:
1. BIRTH
2. EXAM
3. TIRED
4. PARENT
5. TEST
6. MOTHER
7. CAREFUL
8. NUTRITION
9. DOCTOR
10. NURSE
11. FETUS
12. TWINS
2. EXAM
3. TIRED
4. PARENT
5. TEST
6. MOTHER
7. CAREFUL
8. NUTRITION
9. DOCTOR
10. NURSE
11. FETUS
12. TWINS