Introduction Exposure to tobacco smoke during intrauterine life may lead to a variety of disturbances in development. Intrauterine growth retardation and low birth weight is one of the most commonly faced problems. Over 20% of the low birth weight incidence in the United States may be attributed to prenatal exposure to cigarette smoke. 1 Low birth weight is an important predisposing risk factor to increased neonatal mortality 2 and even if the infants survive the initial few months of their life, they face an increased risk of long-term health issues such as mental deficits, obesity, hypertension, cardiac diseases and diabetes. 3,4 The relationship between tobacco exposure and foetal development has also been confirmed by epidemiological studies. Although the possible underlying pathological mechanisms have not been thoroughly investigated in humans, but animal studies suggest an impact of atmospheric contaminants such as tobacco smoke on placental structure, weight and function. 5 Successful pregnancy demands continuous interactions between the embryo and mother for which the normal structure and functioning of placenta is necessary. The placenta weight which reflects placental structure and function in turn has a nonlinear relation to the birth weight and is an important predictor of birth weight. 6 Placental weight and its ratio to birth weight have recently been reported to predict chronic disease in later life. 7 Previous studies have shown a decrease in placental weight, 8 and multiple histological changes in the placentae exposed prenatally to tobacco smoke 9 which may be responsible for compromised placental functioning, ultimately leading to low birth weight. Tobacco smoke contains many noxious and cancer- causing chemicals, 10 as well as unstable free radicals and reactive oxygen species which have the potential for causing oxidative damage. 11 These are normally counteracted by antioxidants such as vitamin C and E, 12 thereby neutralising the free radicals and their harmful effects. If free radicals are not neutralised by the body, oxidative injury ensues in which the free radicals adversely alter the cell biochemistry and trigger a number of diseases. Therefore, it is suggested that J Pak Med Assoc 383 ORIGINAL ARTICLE Role of oxidative injury in affecting the foetal & placental weights on exposure to tobacco smoke Huma Musarrat Khan, 1 Muhammad Yunus Khan, 2 Liaqat Ali Minhas 3 Abstract Objective: To investigate the role of oxidative injury in affecting foetal and placental weights in mice by exposing them to tobacco smoke with or without supplementation with antioxidants. Methods: The randomized control trial of pregnant mice at day one of gestation was conducted at Anatomy Department CPSP Regional Center Islamabad, from March 2005 to October 2005. The mice were divided into three groups: Group C had controls, while the two other groups, groups S and SV were exposed to secondary tobacco smoke in a whole body exposure chamber with and without supplementation with vitamins respectively. At term, the animals were sacrificed and the placentae and foetuses were weighed. The average values were calculated. The means for each group were analysed and the foetal placental ratio was calculated. SPSS 17 was used for statistical analysis. Results: There were 44 mice; 15(34%) each in S and SV groups, while Group C had 14(32%) mice who acted as the controls. The mean foetal weight in Group S was 0.65±0.52g which was significantly less (p<0.0001) than1.48±0.19g in Group C. The mean foetal weight in Group SV was 0.97±0.65g which was not significantly different from S (p=0.124). The mean placental weight in Group S was 0.16±0.02g which was significantly less than 0.21±0.05gin Group C (p=0.014). In Group SV it was significantly more than Group S (p<0.0001). The ratio of mean foetal and mean placental weights in the groups C, S and SV were 7.05, 3.92 and4.41 respectively. Conclusion: Prenatal exposure to tobacco smoke decreased the mean foetal and placental weights and the foetal- placental ratio. This may partly be attributed to oxidative injury induced by free radicals in the tobacco smoke as it is prevented to some extent by simultaneous administration of antioxidants. Department of Anatomy, 1 Foundation University Medical College, 2 CPSP Regional Center Islamabad, 3 Rawal Institute of Medical Sciences, Rawalpindi. Correspondence: Huma Musarrat Khan. Email: huma.anat@gmail.com