| LMP* | CRL* | Gross apearance & internal development |
| 5mm | 3mm | Optic vesicles appear. Double heart recognized. Pregnancy test is positive. |
| 6mm | 4mm | Head is bent forward; limbs are bumps, tail prominent. Initial stage of most organs has begun. |
| 10mm | 30mm | Eyes, ears, nose, mouth recognizable; digits formed, tail almost gone. Sensory organ development well along. Random movement is seen on ultrasound. |
| 14mm | 80mm | Skin pink, delicate; resembles a human being, but head is disproportionately large. Brain configuration roughly complete. Internal sex organs now specific. Bone marrow producing blood. Bones are hardening. Genetic testing by amniocentesis is possible. |
| 18mm | 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. |