Dr Alison Kelly, senior registrar at the Withington hospital, found that 40 per cent of the women in her trial were depressed enough to warrant medical treatment in the thirty-sixth week of pregnancy.
Dr Kelly said she now believes that only in a small number of cases is the depression truly triggered by the birth. Most of the women are already clinically depressed, with the depression caused by the pregnancy. After birth they can be treated for low oestrogen levels, or with non-sedative anti-depressant drugs.
Dr Kelly's research into post- natal depresssion is important because most studies have been retrospective and have not tested the mental health of women during their pregnancies.
Last week, at an international meeting in Nice, France, Dr Kelly described how 100 pregnant women and 44 in a control group of non-pregnant women matched for age, number of children and social class, and friends of the pregnant women, took part in the research. All completed a standard psychological questionnaire to test the state of their mental health and had a blood test to detect hormone imbalance at 36 weeks of pregnancy, and three days after the births.
Two months after the births, 77 of the mothers and 33 controls were questioned again. At this stage, 11 of the new mothers (about 15 per cent) were depressed. Nearly all scored 'high blues ratings' in pregnancy - only four were found to have 'new' post-natal depression.
Women with the lowest oestrogen levels in pregnancy and afterwards were still likely to be depressed six months after the birth, she added. 'The finding that 40 per cent of the pregnant women could loosely be called ill at 36 weeks was very surprising. It was significantly higher than in the controls. About one-third of these did get better after the birth. The others can be supported or counselled during the remainder of their pregnancy and treated, if necessary, after the birth.'
Dr Kelly said that studies had shown that between 10 and 20 per cent of women suffered from post- natal depression, with a suicide rate of 15 per cent. One in 50,000 will kill her baby. 'Aside from that, the child of a depressed mother is likely to suffer . . . behaviour disturbances at the age of three or four, particularly in terms of social development.'
Cultural pressure on women to look forward to the 'happy event' was a serious barrier to treatment, she said. 'There is enormous prejudice among GPs over depression in mothers and they are even less likely to pick it up in pregnancy.'
Treatment needed to be chosen carefully. 'No new mother, even with the most wicked sleep disturbance, will accept a sedative drug for her depression,' she said. Recently she had prescribed anti-depressant drugs to a woman in the survey. 'This woman had been suffering from depression for three months. But the GP refused her a repeat prescription. He said she had a husband and two healthy children and there was no way she could possibly be depressed.'