Appropriate descriptive statistics were used to sum marise the out comeand
risk variables. Frequencies and percentages were used for categorical
variables,while means and standard deviations (SD)were used
for continuous variables. Statistical analyses were undertaken to estimate
the association between the exposure variables and birth weight
(using birth weight z-score (BWZ)). Pearson's χ2-test was used to
check for differences between the analytical study sample and other
participants in the Bt20+cohort who were not included in the analyses.
Bivariate analyses were conducted to determine the unadjusted association
between respective exposures and the outcome.
Following bivariate analyses,multiple linear regression models were
used to determine risk factors independently associated with infant
birth weight and to estimate the strength of the adjusted associations.
A probability value of p b 0.05 was designated for statistical significance
and all analyses were conducted using Stata 13.1 (Stata Corporation,
College Station, Texas, USA).