Table 1
Genetic and environmental contributions (%) to birth weight variation (adapted from James & Stephenson3)
| Genetic | |
| Maternal genotype | 20 |
| Fetal genotype | 16 |
| Fetal sex | 2 |
| Total genetic contribution | 38 |
| Environmental | |
| General maternal environment | 18 |
| Immediate maternal environment | 6 |
| Maternal age and parity | 8 |
| Unknown environmental influences | 30 |
| Total environmental contribution | 62 |
