The fetal heart rate is much faster than an adult’s (or even a child’s) heart rate. The average adult resting heart rate is 60 to 80 beats per minute. The normal fetal heart rate is 110 to 160 beats per minute.
During the early weeks of development there is great change from embryo to fetus but the overall size of the embryo is very small. As the pregnancy continues, weight gain and overall size become much more significant. Until the twentieth week of pregnancy, length measurements are from the crown (or top) of the head to the rump. After the twentieth week, the fetus is less curled up, and measurements are from the head to toe.
| Average Size of the Fetus during Pregnancy |
| Gestational Age |
Size |
Weight |
| 8 weeks |
0.63 inches (1.6 cm) |
0.04 ounce (1 gram) |
| 12 weeks |
2.13 inches (5.4 cm) |
0.49 ounce (14 grams) |
| 16 weeks |
4.57 inches (11.6 cm) |
3.53 ounces (100 grams) |
| 20 weeks |
6.46 inches (16.4 cm) |
10.58 ounces (300 grams) |
| 24 weeks |
11.81 inches (30 cm) |
1.32 pounds (600 grams) |
| 28 weeks |
14.80 inches (37.6 cm) |
2.22 pounds (1,005 grams) |
| 32 weeks |
16.69 inches (42.4 cm) |
3.75 pounds (1,702 grams) |
| 36 weeks |
18.66 inches (47.5 cm) |
5.78 pounds (2,622 grams) |
| 40 weeks |
20.16 inches (51.2 cm) |
7.63 pounds (3,462 grams) |
