Prevalence: Substance use in young women (16-24 years old) has increased in the last decade. Twenty-four per cent of young women aged 16-24 are 'heavy drinkers' (defined as more 6 units in a day on at least one day in the previous week). Several studies conducted in the UK in the 1990s on different populations of pregnant women demonstrated nicotine use in about a third of pregnant women, cannabis use in about 11%, opiate use in less than 2% and cocaine use is about 1%. Other studies confirmed that 10.6-15.6% of antenatal women will be using substances other than tobacco in the first trimester and when objective measures on women in labour were reported about 3.5% had evidence of substances other than tobacco. Consequences: It is estimated that at least a quarter of a million children are growing up in homes where one or both parents have drug problems which may expose them to social and environmental hazards in the UK. The National Confidential Enquiry into Maternal Deaths found that the overall leading cause of pregnancy related death is psychiatric disorder, and 8% of all mothers who died were substance users especially young disadvantaged women who were up to 20 times more likely to die than those from advantaged groups. Impact on the fetus: Studies on the impact of substance misuse on the fetal growth remains relatively under-researched. Smoking in pregnancy is associated with low birth weight, shorter length and increased perinatal mortality. Apart from fetal alcohol syndrome, a major cause of preventable learning disability. Some studies report that cannabis using mothers are some likely to have preterm delivery, minor physical abnormalities, reduced birth length and weight; cocaine use is associated with placental abruption while heroin use is associated with reduced birth weight. There is very little recent research on this topic in the UK. Screening and assessment tools: The variation in reported prevalence is related to different methods of assessment from self report to meconium analysis. Few studies have used objective measures or structured interviews. Studies were also undertaken at different gestational stages in different settings. Substance use in women is underdetected in maternity units and recent robust information on prevalence is not available. In light of the above, this presentation will present a prevalence survey undertaken to establish the nature and extent of substance misuse in pregnant women presenting for scans at 20 weeks gestation.