Debate RISK FACTORS OF LOW BIRTHWEIGHT A Comment

Dr A. Bener and colleagues have reported socio-demographic risk factors associated with low birthweight in United Arab Emirates by conducting a case-control study. In a case-control study, individuals selected as controls should not only be free of the study disease, but should also be similar to the cases in regard to past potential for exposure during the time period of risk under consideration. In this study there is a possibility that cases and controls differ in factors like maternal age, maternal weight-gain and maternal diseases like anaemia, hypertension and toxaemia. The authors have not taken into account these factors, either in the selection process or at the analysis stage. Therefore these factors can act as confounding factors and may affect the validity of the study. Borros et al. (1985) have observed that the above mentioned factors increase the risk of low birthweight babies. The Mantel–Haenszel procedure is used to calculate the summary or adjusted odds ratio from a stratified analysis to control the effect of confounding (Schlesselman, 1982). Although the authors have mentioned that the Mantel–Haenszel procedure was used to calculate the odds ratios in Tables 1 and 2, it appears that only crude odds ratios were computed without any stratification. It is appropriate to use the Mantel–Haenszel procedure or multiple logistic regression analysis to compute adjusted odds ratios after taking into account the confounding factors.