3D vs 4D Ultrasound: What's the Difference?

3D and 4D ultrasound are two of the most requested scans among expecting parents, and the terms are often used almost interchangeably — but they're not quite the same thing.

3D ultrasound: a still, detailed image

A 3D scan takes many 2D ultrasound slices and combines them into a single detailed, still three-dimensional image — giving a much clearer sense of your baby's face and features than a standard 2D scan.

4D ultrasound: 3D images in motion

A 4D scan is essentially a 3D scan with the fourth dimension being time — so instead of one still image, you see a live-motion video, catching real-time movements like a yawn, a stretch, or a hand near the face.

When is the best time to get one done?

The window between 26 and 30 weeks of pregnancy is generally considered ideal — by this stage the baby has enough facial fat for clear features to show, while there's usually still enough room and fluid for active movement.

Beyond the keepsake value, these scans are performed by the same radiologist team reviewing your pregnancy's health — so it remains a medical scan first, with the reassuring images as a welcome bonus.