Table 7.
Multivariate regression model to assess the relationship of head circumference (cm) with fetal dose, restricted to individuals with data taken from medical records, or medical records and logs
| Parameter estimate (+95% CI) | 2-sided P value | |
|---|---|---|
| Fetal dose (cm/Gy) | −0.954 (−1.493, −0.329) | 0.005 |
| Trimester 1 versus trimester 3 | −0.214 (−0.524, 0.054) | 0.134 |
| Trimester 2 versus trimester 3 | −0.188 (−0.488, 0.060) | 0.176 |
| Parity ≥1 versus parity 0 | 0.036 (−0.217, 0.267) | 0.771 |
| Gestation weeks (cm/week) | 0.307 (0.214, 0.413) | <0.001 |
| Baby sex female versus baby sex male | −0.307 (−0.543, −0.095) | 0.008 |
| Twin versus singleton | −1.190 (−2.709, −0.284) | 0.010a |
| Maternal age (cm/year) | 0.010 (−2.930, 2.793) | 0.936 |
| Maternal height (cm/cm) | 0.005 (−0.033, 3.470) | 1.000 |
| Maternal weight at 1st clinic (cm/kg) | 0.059 (0.031, 0.138) | 0.010 |
| Model with separate dose × trimester | ||
| Dose in trimester 1 (cm/Gy) | −7.072 (−28.770, 53.512) | 0.660 |
| Dose in trimester 2 (cm/Gy) | −1.504 (−2.326, −0.716) | 0.003 |
| Dose in trimester 3 (or missing) (cm/Gy) | −0.275 (−1.121, 0.867) | 0.541 |
| Linear quadratic model in dose | ||
| Linear dose (cm/Gy) | −1.163 (−2.561, 0.304) | 0.113 |
| Quadratic dose (cm/Gy2) | 0.206 (−0.936, 1.335) | 0.709 |
a
P value derived from BCA-confidence intervals via Normal distribution
All regressions evaluated using 4999 bootstrap resamples. Model adjusted for trimester of exposure, parity, gestation weeks, baby’s sex, singleton/twin birth, maternal age at delivery of offspring, maternal height and maternal weight at first clinic visit. The estimates for the constant term and for indicators of covariate missingness are not given. Analysis of n = 887 persons with non-missing data on head circumference and fetal dose, with data taken from medical records and/or logs