Background: Risk factors for pregnancies being complicated by the birth of a small-for-gestational age (SGA) infant were analysed in a socio-economically disadvantaged area, with separate analysis for population-based and customized-based birth weight percentiles.
Methods: A retrospective case-controlled study of all singleton pregnancies resulting in the birth of an infant with a birth weight < 10 population-based centile, born in the Northern suburbs of metropolitan Adelaide, between 1998 and 2003. Significant risk factors in the univariate analysis were subsequently checked with multivariate analysis.
Results: The analyses confirm marked differences between population-based and customized-birth weight centiles. Patterns of risk factors show clear differences in risk factors for these two different SGA groups. Univariate analyses of all (nulliparous and multiparous women) customized SGA infants shows us the following odds ratio's (OR); unemployment OR 2.06, 95% confidence interval (CI) 1.46-2.92, being a single mother OR 1.90, CI 1.76-2.05, smoking OR 3.24, CI 2.32 - 4.54, recreational drug use OR 2.40, CI 1.55-3.70, mental health problems OR 1.52, CI 1.04-2.23, domestic violence OR 3.42, CI 1.26-9.29, being healthy OR 0.43, CI 0.30-0.61, preeclampsia OR 1.73, CI 1.01-2.97, and BMI < 30 OR 0.63 CI 0.43-0.93. Length of pregnancy interval had no relationship whatsoever with the risk of being delivered of an SGA infant. Multivariate analyses for customized SGA showed five factors with an OR > 2 (95% CI not crossing 1), including unemployment, smoking, maternal age > 34 years, not being healthy and preeclampsia, while different paternity, age 25-34 compared to age < 25 were also found to be significant risk factors. Higher systolic blood pressure was found to convey significant protection.
Conclusion: When studying risk factors for pregnancies complicated by the birth of an SGA infant, both population-derived and customized growth centiles should be utilized. This study confirms the importance of smoking as a major risk factor, our data also show major protection being conveyed by having a regular job and being generally healthy. Pregnancy interval did not have any relationship with the birth of SGA infants, while paternity change was identified as a clear risk factor. Although genuine preeclampsia persists as a clear risk factor, higher systolic blood pressure appears to convey protection.