Table 2.
The association of parental body mass index with infant birthweight, examining the influence of nonlinearity and a pairwise linear interaction.
| Parental interactions | M0 (linear BMI) |
M1 (linear + int) |
M2 (non-lin mat-BMI + int) |
M3 (non-lin BMI + int) |
||||
|---|---|---|---|---|---|---|---|---|
| Est (g) [95% CI] | P value | Est (g) [95% CI] | P value | Est (g) [95% CI] | P value | Est (g) [95% CI] | P value | |
| Mat BMI (linear) | 11.2 [7.2, 15.1] | <.001 | 12.2 [8.2, 16.2] | <.001 | 33.7 [12.1, 55.3] | <.001∗ | 33.9 [12.2, 55.6] | <.001∗ |
| Mat BMI (nonlinear 1) | −152 [−316, 12] | −156 [−320, 9] | ||||||
| Mat BMI (nonlinear 2) | 310 [−37, 657] | 318 [−31, 667] | ||||||
| Pat BMI (linear) | 2.0 [−3.1, 7.1] | .44 | 4.4 [−1.0, 9.9] | .11 | 4.2 [−1.3, 9.7] | .13 | 4.0 [−18.3, 26.2] | .10∗ |
| Pat BMI (nonlinear 1) | 26 [−75, 126] | |||||||
| Pat BMI (nonlinear 2) | −110 [−424, 204] | |||||||
| Mat BMI (linear) × Pat BMI (linear) | −0.88 [−1.49, −0.27] | .005 | −0.79 [−1.5, −0.1] | .02 | −0.56 [−1.31, 0.20] | .15 | ||
Note: BMI = body mass index; Mat = maternal; Pat = paternal; lin = linear; int = interaction. ∗A single P value is reported for all nonlinear terms. The base model M0 includes just the two parental BMIs linearly. Model M1 extends M0 with the inclusion of the pairwise linear interaction of parental BMIs. Model M2 extends M1 with the inclusion of nonlinear terms for maternal BMI. Model M3 is the full model with nonlinear terms for both parental BMIs and their pairwise linear interaction. The following adjustment factors were included in the models: gestational age, parental age, Socio-Economic Indexes for Areas score, year of delivery, and delivery method.