Table 3.
Three-Level Model Showing Associations Between Infant Birth Weight, Interpregnancy Interval, and Diurnal Cortisol Slope Sampled during Interpregnancy or Pregnancy: Fixed Effects With Robust Standard Errors
| Model for Interpregnancy Cortisol (n = 99) | Model for Pregnancy Cortisol (n = 114) | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|
|
| ||||||||||
| Fixed effects | Estimate | (SE) | t ratio | df | p | Estimate | (SE) | t ratio | df | p |
| Cortisol intercept (morning) | 1.34 | 0.11 | 11.73 | 93 | <0.001 | 1.51 | 0.11 | 14.06 | 108 | <0.001 |
| Level 2 covariates | ||||||||||
| Days gestation | -- | -- | -- | -- | -- | 0.002 | 0.00 | 3.65 | 110 | <0.001 |
| Level 3 covariates | ||||||||||
| Infants’ Birth Weight | −0.03 | 0.06 | −0.54 | 93 | 0.588 | 0.05 | 0.06 | 0.90 | 108 | 0.370 |
| Interpregnancy Interval | −0.00003 | 0.00032 | −0.10 | 93 | 0.920 | 0.0006 | 0.00 | 2.39 | 108 | 0.019 |
| Household income | 0.000001 | 0.000002 | 0.58 | 93 | 0.561 | 0.00001 | 0.00 | 2.72 | 108 | 0.008 |
| Cohabitation | −0.04 | 0.17 | −0.22 | 93 | 0.826 | −0.10 | 0.12 | −0.82 | 108 | 0.415 |
| African-American | −0.61 | 0.16 | −3.80 | 93 | <0.001 | −0.31 | 0.12 | −2.63 | 108 | 0.010 |
| Cortisol slope (time) | −0.09 | 0.01 | −16.70 | 201 | <0.001 | −0.10 | 0.01 | −13.10 | 327 | <0.001 |
| Level 2 covariates | ||||||||||
| Days gestation | -- | -- | -- | -- | -- | 0.0002 | 0.00 | 4.30 | 327 | <0.001 |
| Level 3 covariates | ||||||||||
| Infants’ Birth Weight | −0.010 | 0.004 | −2.23 | 201 | 0.027 | −0.008 | 0.00 | −2.15 | 327 | 0.032 |
| Interpregnancy Interval | 0.00005 | 0.00003 | 1.80 | 201 | 0.074 | −0.00004 | 0.00 | −2.63 | 327 | 0.009 |
| Household income | 0.000000 | 0.000000 | −0.83 | 201 | 0.408 | 0.000000 | 0.00 | −1.34 | 327 | 0.182 |
| Cohabitation | −0.02 | 0.01 | −1.68 | 201 | 0.094 | 0.004 | 0.00 | 0.49 | 327 | 0.628 |
| African-American | 0.10 | 0.01 | 7.71 | 201 | <0.001 | 0.064 | 0.00 | 7.98 | 327 | <0.001 |
| CAR | 0.16 | 0.08 | 1.96 | 201 | 0.051 | 0.16 | 0.05 | 3.14 | 327 | 0.002 |
| Sample clarity | 0.21 | 0.11 | 1.87 | 201 | 0.063 | 0.01 | 0.06 | 0.18 | 327 | 0.858 |
Notes. Pregnancy trimester coded as 0 for preconception study days, 1 for first trimester, 2 for second trimester, and 3 for third trimester. Interpregnancy interval calculated as difference between birth of index child and LMP. Sampling time is centered around wake time = 5 am. Household income is adjusted for cost of living differences across study sites. Variable names for Level 1 indices (intercept, slope, CAR, and sample clarity) are presented in bold font.