Background: The extent to which smoking and drinking in a local community is associated with nutrition and Z-scores of infants from spontaneous preterm deliveries, is uncertain. Aim: To investigate associations of different levels of maternal smoking and drinking in spontaneous preterm birth with infant birthweight Z-scores.
Methods: Information, including gestational age (determined by earliest ultrasound), maternal arm circumference (measured at enrolment), smoking-drinking data (obtained up to 4 occasions), birthweight data (obtained from medical records) and birthweight Z-scores (calculated from INTERGROWTH- 21st study), collected over a period of nine years was used to compare 407 spontaneous preterm births with 3 493 spontaneous term births Analyses of variance, correlations and multiple regression were performed in STATISTICA.
Results: Women with spontaneous preterm birth, had significantly lower gravidity and smaller arm circumference when compared to women with spontaneous birth at term. Women with spontaneous preterm birth drank more and heavier during pregnancy, and more smoked. Gestational age at birth was significantly longer in heavy-smokers-heavy-drinkers compared to heavy-smokers-no-drinkers (7.1 days) and in no-smokers-heavy-drinkers when compared to no-smokers-no-drinkers (11.2 days). Birthweight was significantly lower in low-smokers-heavy-drinkers when compared to low-smokers-no-drinkers (240g) and in heavy-smokers-lowdrinkers when compared to no-smokers-low-drinkers (273g). Birthweight Z-scores were significantly lower in low-smokers-heavy-drinkers when compared to lowsmokers- low-drinkers and low-smokers-no-drinkers; and, also significantly lower in heavy-smokers-low-drinkers when compared to low-smokers-low-drinkers and no-smokers-low-drinkers.
Conclusion: Alcohol aggravates the detrimental effect of smoking on birthweight and birthweight Z-scores but seems to counteract the negative association of smoking with gestational age.
Spontaneous preterm birth, Pregnancy, Cigarette smoking, Alcohol drinking, Gestational age, Birthweight, Birthweight Z-Scores
Preterm birth is a critical global health problem and a major challenge in perinatal health care because of its high morbidity and mortality . It does not only affect infants and their families but also increases costs of health care [2,3]. Perinatal outcome is particularly susceptible to socio-economic conditions affecting lifestyle choices and behavioural factors .
Substance use during pregnancy, including cigarette smoking and alcohol consumption [5-7], has been linked to adverse birth outcomes such as preterm birth, low birth weight, and fetal growth restriction [8-10]. Smoking during pregnancy increased the risk of preterm birth nearly two-fold with a dose response further increasing the risk .
Worldwide, significant numbers of women still drink heavily during pregnancy despite public health advisories, psychosocial interventions , and detailed information on the adverse effects of smoking and drinking . South Africa has one of the highest levels of alcohol consumption, heavy binging as well as heavy smoking in certain communities [13,14].
Birthweight and duration of gestation are important predictors of health and survival of new-borns  with birthweight the best marker of optimal fetal growth and development . Nutritional status, reflected by the maternal mid-upper arm circumference, is an important contributor to infant birthweight , is an indicator of the progress of pregnancy and its outcome , and is significantly associated with preterm births [15,18].
The Safe Passage Study (SPS) by the PASS Network was a large prospective multidisciplinary study to investigate the associations of smoking and drinking during pregnancy with stillbirths and infant deaths . Detailed information on various aspects of pregnancy, labour and neonatal outcome was collected within geographically defined communities. Analysis of the South African part of the data demonstrated a high preterm birth rate of 13.8% , in sharp contrast to the rate of 5.4%-8.9% for 24 European countries in 2010 .
Synergistic interactions between smoking and drinking lead to higher rates of preterm birth than predicted by their additive effects [22,23]. As the co-occurrence between tobacco and alcohol use is well established , the South African SPS data presented an ideal opportunity to investigate the association of smoking and drinking with maternal arm circumference, gestational age, birthweight, and their combined effect on infant birthweight Z-scores in spontaneous preterm birth.