Step 1: Identify the governing law. In India, prenatal sex determination and disclosure are regulated by the Pre-Conception and Pre-Natal Diagnostic Techniques (Prohibition of Sex Selection) Act, 1994 - the PC-PNDT Act. Its purpose is to prevent female feticide and the falling sex ratio. The woman here is explicitly requesting sex determination so she can have a boy, which is precisely the sex-selective demand the Act prohibits.
Step 2: What the law permits and forbids. The Act allows prenatal diagnostic procedures (ultrasonography, etc.) when there is a valid medical indication - to detect chromosomal/genetic disorders, congenital malformations and other fetal developmental abnormalities. The Act strictly forbids communicating the sex of the fetus to the pregnant woman, her relatives or any other person by words, signs or any other manner. Therefore the correct conduct is to perform the routine antenatal scan and look for developmental/structural abnormalities, but not reveal the gender to the patient.
Step 3: Why the other options are wrong.
(B) Revealing the gender to the patient directly violates the PC-PNDT Act and is a punishable offence.
(C) Revealing the sex 'if a girl' (or in any conditional manner) is still disclosure of fetal sex and is equally prohibited; it would in fact facilitate sex-selective abortion.
(D) Refusing to do the ultrasound sex/abnormality check altogether is wrong because a medically indicated antenatal scan to look for fetal anomalies is legitimate and should not be withheld; the Act bans sex disclosure, not the scan itself.
Final answer: A - Do the routine ANC scan, screen for developmental abnormalities, and do not reveal the gender to the patient.