This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: All India exam, Subject name: Microbiology
Which of the following evaluation method is most sensitive in diagnosing pregnancy early? 
Select and explain. 
A. Serum pregnancy test, B. Detection of fetal hea tones by Doppler equipment, C. Abdominal ultrasound, D. Bimanual exam to assess uterine size
A: Serum pregnancy test
Answer: A: Serum pregnancy test 
Explanation: A Doppler instrument will detect fetal cardiac action usually no sooner than 10 weeks.A sensitive serum pregnancy test can detect placental HCG levels by 8 to 9 days post-ovulation, and it is, therefore, the most sensitive modality for detecting and diagnosing pregnancy.