Table 4. Difference between ultrasound and LMP or New Ballard-determined gestational age by maternal and infant characteristics.
| Gestational age difference (New Ballard-US), weeksa |
Gestational age difference (LMP-US), weeks |
|||
|---|---|---|---|---|
| Mean difference (sd) | Difference of the differenceb (95% CI) |
Mean difference (sd) | Difference of the differenceb (95% CI) |
|
| Gestational age at ultrasound (per extra week) | - | -0.18 (-0.26, -0.10) | ||
| Recall | ||||
| Exact date | 0.11 (1.90) | Reference | ||
| Month only | 0.24 (2.62) | 0.46 (-0.29, 1.21) | ||
| Years of school | ||||
| Primary or less | 0.12 (2.1) | Reference | ||
| Greater than primary | 0.18 (1.9) | 0.01 (-0.63, 0.65) | ||
| Age | ||||
| ≤23 years | 0.20 (2.16) | Reference | ||
| > 23 years | 0.07 (1.89) | -0.18 (-0.77, 0.41) | ||
| Ethnicity | ||||
| Spanish speaking | 0.40 (1.65) | Reference | 0.43 (1.84) | Reference |
| Mam only | 0.67 (1.54) | 0.32 (-0.21, 0.85) | 0.06 (2.09) | -0.41 (-1.07, 0.26) |
| Gender | ||||
| Male | 0.88 (1.54) | Reference | -0.21 (2.01) | Reference |
| Female | 0.38 (1.55) | -0.32 (-0.77, 0.14) | 0.43 (2.01) | 0.46 (-0.11, 1.03) |
| Term status | ||||
| Full-term | 0.39 (1.48) | Reference | -0.02 (1.87) | Reference |
| Preterm | 1.97 (1.40) | 1.52 (0.87, 2.17) | 0.94 (2.61) | 0.98 (0.19, 1.77) |
| SGA | ||||
| Non-SGA | 0.88 (1.54) | Reference | 0.26 (2.16) | Reference |
| SGA | 0.05 (1.47) | -0.83 (-1.31, -0.34) | -0.10 (1.56) | -0.18 (-0.70, 0.43) |
a Gestational age at ultrasound, recall of the LMP, and maternal age and education were assumed to be independent of the accuracy of the nurse-administered New Ballard and thus were not included for analysis
b Difference of the difference holding all other variables constant calculated as the β from multivariate linear regression using all maternal and infant characteristics as explanatory variables