While the results may not be representative of the UK as a whole, nevertheless, excess drinking and drug taking in pregnancy is a pairing that is likely to be more common than generally thought, say the authors.

It is known that women prescribed maintenance methadone use other illicit drugs, but the extent to which they do this has never been quantified in the UK, nor are there any figures on the prevalence of drug and alcohol use during pregnancy for this group of women, they add.

They interviewed 56 mums who were on methadone maintenance during their pregnancy and carried out tox screens of the mums' and babies' urine, as well as meconium -- first stools -- within 3 days of birth -- to gauge levels of exposure to drugs and alcohol in the womb.

The samples were tested for opiates, benzodiazepines, amphetamines, cannabinoids, and cocaine, as well as fatty acid ethyl esters (FAEEs), which are by-products of alcohol consumption and indicate more than 2 units a day or more than 5 units in one go.

Most of the babies (51; 91%) had been exposed to other illicit drugs while in the womb, mostly opiates (73%) and benzodiazepines (70%). And 59% had been exposed to cannabinoids, 14% to amphetamines, and 7% to cocaine. The most common drug combo was opiates, benzodiazepines, and cannabinoids.

Almost half the babies (47%; 21) also had high FAEE levels, although only 5% of their mums admitted to drinking more than 7 units of alcohol a week during their pregnancy, a finding that has "significant implications" for the longer term health of an already vulnerable group of babies, say the authors.

Meconium analysis picked up prenatal drug and alcohol exposure far better than either urine analysis or interview, prompting the authors to comment: "It is well recognised that pregnant women under report illicit drug and alcohol use in pregnancy, often due to a fear of legal and custodial repercussions."

The pattern of drug and alcohol use in pregnancy will vary from region to region, they admit, but go on to say: "It seems likely, nevertheless, that excessive alcohol consumption is more commonly associated with drug misuse in pregnancy than is generally recognised."