Ay, usually around 18-20 weeks ang congenital anomaly scan, kaya it's also called the mid-pregnancy ultrasound, that's when the baby is developed enough na makita ng sonographer yung details nila, from the heart to the spine to lahat ng organs. A few of us had ours scheduled exactly at 19 weeks, pero depende talaga sa clinic mo at kung kelan nila available, so best to confirm with your OB kung anong week ang recommended para sayo!