A fetal anomaly scan is a detailed ultrasound performed around 18–21 weeks of pregnancy to examine the baby’s anatomy and detect major structural abnormalities. It evaluates the brain, heart, spine, limbs, placenta location, amniotic fluid and number of fetuses. Results help guide further testing, specialist referral or pregnancy planning. It is routine but does not detect every possible condition.

The anomaly (mid‑trimester) ultrasound is mainly to check fetal anatomy, but it can often reveal fetal sex from about 18–20 weeks. Accuracy is high when the genital area is clearly seen, yet it isn’t guaranteed. Visibility depends on fetal position, gestational age, placenta location, maternal body habitus and operator skill. Some clinics or regions may not disclose sex for legal or policy reasons.

I'm not aware of a universally used "rule of 3" for the anomaly scan. Do you mean the three‑vessel view used to assess the fetal heart, the idea of checking three main areas (fetal anatomy, placenta, growth), or the timing guideline of a single detailed scan offered around 18–20 weeks? Tell me which you mean and I’ll give a concise explanation.

Anomaly scan is usually done between 18 and 22 weeks of pregnancy, which corresponds to the late fourth or early fifth month. This mid-pregnancy detailed ultrasound checks fetal anatomy and growth. Timing may vary slightly depending on local protocols or if earlier imaging is needed; follow your obstetrician’s guidance to schedule the scan within this window.

Doctors suggest an anomaly scan (typically at 18–22 weeks) to check fetal anatomy and development, identify major structural abnormalities (brain, heart, spine, limbs, face), confirm gestational age and number of fetuses, assess placenta and amniotic fluid, and spot markers that may indicate genetic issues. Findings guide further testing, prenatal care, counseling and planning for delivery or specialist care if anomalies are found.

Anomaly (20-week) scan prices vary: on public systems like the NHS it's usually free. Privately, expect roughly £100–£300 in the UK, $100–$500 in the US (often covered by insurance), and about ₹600–₹5,000 in India depending on city and facility. Costs depend on clinic, equipment and included reports; always confirm exact fees and insurance coverage before booking.