How much does crack cocaine hurt babies in the womb? There was an interesting and sobering answer to that question in The Philadelphia Inquirer yesterday.

Researchers in Philadelphia, led by Prof. Hallam Hurt, started studying the question in 1989. With one in six new mothers in the area testing positive for crack, they arranged a sample of 224 babies, all from poor local families. Half of the mothers had used cocaine during pregnancy, half hadn’t.

The study has run for 25 years and cost $9m. The point of it was to ascertain what kind of damage drug use did to unborn babies, for the sake of treatment and public education.

In fact the study produced a completely different result. They found, on the one hand, that there were no big differences between the two groups. IQ at the age of four, for example, was 79 for exposed children and 82 for the non-exposed – a small gap considering the national average is around 100.

But that was the other thing that struck them. The basic mental development of both groups was seriously held back, compared to the national average. What they had in common was that they were from poor, inner-city households. So the researchers looked into that as well as drug use. Across both groups, they found the effects of poverty devastating. A quarter, in each case, started school with abnormally low maths and language abilities. Four out of five had seen someone arrested. 35% had seen someone shot. And exposure to violence correlated to depression, anxiety and low self-esteem.

Professor Hurt’s conclusion is as clear as it was unforeseen. She says: “Poverty is a more powerful influence on the outcome of inner-city children than gestational exposure to cocaine.”