Quintuplet foetuses. Ultrasound scan of quintuplet foetuses (black blobs) at 6 weeks. Non-identical (dizygotic) quintuplets develop when five separate eggs are released from the ovaries and are fertilized simultaneously. Identical (monozygotic) quintuplets occur when cells formed by the first divisions of a fertilized egg develop independently. The quintuplets may also be a combination of identical and non-identical siblings. Multiple births are more common in women receiving fertility treatment. Ultrasound scanning is a diagnostic technique that sends high- frequency sound waves into the body via a transducer. The returning echoes are recorded and used to build an image of an internal structure.