Risk factors for small for gestational age as defined by a birthweight z-score below minus one: A prospective observational study.

Objective: To determine the maternal risk factors for small-for-gestational-age newborns as defined by a birthweight z-score (BWZS) < -1.0.

Design: A prospective cohort study with recruitment from August 2007 to January 2015.

Setting: Recruitment at a community health centre with assessments at Tygerberg Academic Hospital, Cape Town, South Africa.

Population: A largely homogeneous population in a low socioeconomic residential area in Cape Town.

Methods: This study is a further analysis of the data of the Safe Passage Study which investigated whether exposure to alcohol and tobacco was associated with increased risk of stillbirth and sudden infant death syndrome (SIDS).

Main outcome measures: Birthweight z-score < -1.0.

Results: Individual odds ratios (ORs), in descending order, were associated with smoking, drinking, and preeclampsia (2.45), previous stillbirth (1.85), smoking (including smokers only and drinkers who also smoked) (1.55), preeclampsia (1.52), smoking and drinking (does not include smokers only or drinkers only)(1.43), hypertension (1.28), drug use (1.24), drinking during pregnancy (including drinkers only and drinkers who also smoked) (1.18), thoughts of self-harm (1.13), and crowding (1.10). After multiple logistic regression, highly significant ORs were found for previous stillbirth (1.89), cigarette smoking (1.84), hypertension (1.40), education (0.94) and body mass index (BMI) (0.95). Thoughts of self-harm then had an OR of 1.08 (95% confidence interval (CI) 1.00-1.18).

Conclusion: Previous stillbirth, cigarette smoking, hypertension, lesser education, and a lower BMI were associated with the highest risks for low BWZS.