Women with drug or alcohol related mental disorders are up to four times more likely to have a low- birth weight baby, an Australian study revealed. The results of the study were outlined on Monday at the annual congress of the Perinatal Society of Australia and New Zealand in Adelaide, the Australian Associated Press (AAP) reported. According to Dr Michelle Bonello from School of Women\'s and Children Health at University of New South Wales, overwhelming new evidence shows that alcohol and drugs lead to low birth weight, preterm birth. \"We believe this study is the tip of an iceberg because the prevalence of women drinking alcohol to excess or taking illicit drugs is increasing and approaching similar levels to men,\" Bonello told AAP. \"Social values of women are changing over time. They are drinking and using drugs.\" She said women admitted to hospital with mental or behavioral problems should be encouraged to use contraception as part of their overall management. The study based on the data of 1,107 first-time mothers found increased risk of low birth weight even if hospitalization took place 12 months before conception.