Table 4.
Commonly used pregnancy‐dating equations and their imprecision in estimating gestational age (GA) (half width of 95% prediction intervals)
| Imprecision in GA estimation (days) for assessment at: | |||||
|---|---|---|---|---|---|
| Reference | R 2 | 12–18 weeks | 18–24 weeks | 24–30 weeks | 30–36 weeks |
| Hadlock et al. (1984)29 | |||||
| BPD | 0.967 | 8.3 | 12.1 | 15.3 | 21.6 |
| HC | 0.973 | 8.3 | 10.4 | 14.4 | 20.9 |
| AC | 0.969 | 11.6 | 14.4 | 15.3 | 20.7 |
| FL | 0.971 | 9.7 | 12.6 | 14.6 | 20.7 |
| HC + BPD | 0.974 | 7.6 | 10.4 | 13.9 | 20.0 |
| HC + FL | 0.976 | 8.4 | 10.6 | 13.9 | 18.8 |
| HC + AC | 0.98 | 7.6 | 9.4 | 13.0 | 17.6 |
| HC + FL + BPD | 0.981 | 7.3 | 9.5 | 12.7 | 17.6 |
| HC + AC + FL | 0.981 | 8.0 | 10.2 | 13.2 | 17.6 |
| HC + BPD + AC + FL | 0.981 | 7.6 | 9.8 | 12.6 | 17.1 |
| Altman and Chitty (1997)30 | |||||
| HC | NR | 8.0 | 13.0 | 17.0 | 22.0 |
AC, abdominal circumference; BPD, biparietal diameter; FL, femur length; HC, head circumference; NR, not reported.