A 3D ultrasound is typically performed in the late second to early third trimester—around months 6–8 of pregnancy (about 26–32 weeks). That window gives the clearest facial and body detail: too early tissues are undeveloped, and after about 32 weeks the baby’s position and reduced space can limit image quality. For medical reasons, timing may vary—follow your clinician’s advice.

A leg ultrasound (Doppler/venous) evaluates blood flow and anatomy in veins and arteries. It detects deep vein thrombosis, assesses varicose veins and venous insufficiency, identifies arterial blockages or peripheral arterial disease, and checks for fluid collections or soft-tissue abnormalities. It’s used to diagnose causes of swelling, pain or discoloration, and to guide treatment or monitor post‑operative recovery.

3D ultrasound produces three-dimensional images of the fetus and surrounding structures, clearly showing surface anatomy like the face, limbs and body contours. It can help detect certain structural abnormalities (for example cleft lip), assess placental position and amniotic fluid, and complements standard 2D scans for evaluating fetal growth and anatomy. It’s often used for diagnostic clarification and parental bonding.

On a 3D ultrasound, sex is identified by visualizing external genitals: a penis and scrotum indicate a boy; three lines or labial folds indicate a girl. Best views are usually at 18–22 weeks when anatomy is clearer. Accuracy depends on fetal position, gestational age, technician skill, maternal body habitus and amniotic fluid. It’s highly but not perfectly reliable; genetic testing is definitive.

The best time for a 3D ultrasound is between 26 and 32 weeks of pregnancy, with an optimal window around 28–30 weeks. At this stage the baby has developed facial fat and there’s usually enough amniotic fluid for clear images, while still enough room to move. Earlier scans show less detail; after 32 weeks the baby may be crowded, reducing image quality.

3D ultrasound creates a static three‑dimensional image by combining many 2D slices into a volumetric picture. 4D ultrasound adds the fourth dimension—time—so the 3D image is shown in real time, displaying fetal movements and expressions. Both use the same ultrasound data and are mainly for clinical assessment; non‑medical scanning should be limited and performed by trained professionals.