During the early weeks of development there are great changes from the embryonic to the fetal stages, but the overall size of the embryo is very small. As the pregnancy continues, weight gain and overall size becomes much more significant. Until the 20th week of pregnancy, length measurements are from the crown (or top) of the head to the rump. After the 20th week, the fetus is less curled up, and measurements are from the head to the toes.
| Gestational Age (weeks) |
Size |
Weight |
| 8 |
0.63 in (1.6 cm) |
0.04 oz (1 g) |
| 12 |
2.13 in (5.4 cm) |
0.49 oz (14 g) |
| 16 |
4.57 in (11.6 cm) |
3.53 oz (100 g) |
| 20 |
6.46 in (16.4 cm) |
10.58 oz (300 g) |
| 24 |
11.81 in (30 cm) |
1.32 lb (600 g) |
| 28 |
14.8 in (37.6 cm) |
2.22 lb (1 kg) |
| 32 |
16.69 in (42.4 cm) |
3.75 lb (1.7 kg) |
| 36 |
18.66 in (47.5 cm) |
5.78 lb (2.62 kg) |
| 40 |
20.16 in (51.2 cm) |
7.63 lb (3.46 kg) |
