DOCTORS in London have succeeded in telling the sex of a baby at less than five weeks after conception by testing the mother's blood.
Their discovery is a first step towards non-invasive testing that could pick up abnormalities in the foetus at a very early stage.
Diagnostic tests for foetal abnormalities such as Down's syndrome are invasive and carry a risk of miscarriage. Identifying and analysing foetal cells from the mother's blood carries no such risk.
While the researchers from St Mary's Hospital, Paddington, University College Hospitals and the London Fertility Clinic say the research is at a very early stage, a blood test would help couples decide if they wanted to terminate a pregnancy within one or two weeks of a first missed period.
The researchers, whose findings are disclosed in a letter in tomorrow's Lancet, were able to identify the sex correctly in two male foetuses and three female by looking for specific DNA sequences, or genetic patterns, from Y, or male, chromosomes. The absence of these sequences indicates the absence of the male chromosomes, showing the foetus was female.
They knew the dates of the conceptions accurately since the women who gave a blood sample were having in vitro fertilisation.
Dr Margot Thomas, of St Mary's Hospital Medical School, who took the blood samples, said yesterday: 'If these (foetal) cells can be purified they could be analysed for DNA mutations in such cases as cystic fibrosis or other diseases where there is a family history. They could be analysed for chromosome errors as in Down's syndrome, very early in pregnancy.'
The researchers believe that the early foetal cells belong to the developing placenta.
Amniocentesis to find abnormalities is carried out at about 16 weeks of the pregnancy and carries a one in 100 or 200 risk of miscarriage. Chorionic villus sampling (CVS), carried out at about 11 weeks, has about double that risk.
The Government has issued a warning following the deaths of two children that people taking corticosteroid drugs who catch chickenpox should seek urgent medical help.
About 30 people a year die of complications arising from chickenpox, one-third of them because their immune system is impaired. The steroid drugs suppress the immune system and the Medicines Control Agency has now ruled that the drugs taken by mouth or injection 'substantially increase the risk of severe chickenpox'.