| LMP (wk)* | CRL (mm)* | Gross apearance & internal development |
| 5w | 3mm | The brain, spinal cord, and heart begin to develop. Pregnancy test is positive. |
| 6w | 4mm | Arm and leg buds become visible. The brain develops into five areas and some cranial nerves are visible. The eyes and ear structures begin to form. Tissue forms that develops into the vertebra and some other bones. The heart continues to develop and now beats at a regular rhythm. Rudimentary blood moves through the main vessels. |
| 10w | 30mm | The eyelids are more developed. External features of the ear begin to take their final shape. The intestines rotate. |
| 14w | 80mm | Skin pink, delicate; resembles a human being, but head is half of fetus size. Genitals appear well differentiated. Limbs are long and thin. The fetus can make a fist with its fingers. |
| 18w | 135mm | Hair and nails appear. Fetus is active. Arm-leg ratio now proportionate. Sex determination possible. External sex organs grossly formed. Heart muscle well developed. |