The number of babies born in Britain with certain birth defects has risen by 50 percent in the past five years, according to research by Birth Defects Foundation, a medical charity. The rise is probably due to environmental factors, say scientists.

Incidences of cleft lip or palate rose from nearly six cases per 10,000 births in 1995 to over nine in 1999, says the charity.

Hypospadias, where the opening to the penis is underneath the shaft, has risen from 7.5 cases per 10,000 to 8.5 and gastroschisis, where the intestines protrude through the abdominal wall, has risen from 1.3 per 10,000 to 1.9, BDF says.

Michael Patton, medical director of BDF and head of medical genetics at St George's Hospital in London, speculates that illegal drug use may be to blame for one of the defects: "Gastroschisis appears to be much more common in babies born of teenage mothers in urban areas and could be due to recreational drug use during pregnancy, although research needs to be carried out to see if this is the case."

Rise and fall

Hypospadias may be linked to the increase of oestrogen-mimicking chemicals in the environment, says Iuen Hughes, professor of paediatrics at Cambridge University. He is carrying out research funded by BDF into the molecular mechanism of the disorder.

"The positioning of the urethra in the developing penis is heavily dependent on coordinated androgen action. Our cellular model shows that oestrogen-like chemicals in the environment interfere with the action of the fetal androgen receptors, causing abnormality," Hughes told New Scientist.

Other birth defects are declining. Incidences of spina bifida has fallen by two-thirds, probably due to women boosting their levels of folic acid in early pregnancy.

The increasing age of first-time mothers was not thought to be significant in neonatal defects because it is linked to increased risk of chromosomal abnormalities such as Down's syndrome. These can be picked up early on in pregnancy and so often lead to termination.

Under-reporting

Patton estimates one in 16 of all babies born have some abnormality ranging from fatal heart defects, deafness or learning difficulties to minor conditions such as a heart murmur or extra tissue growth on a hand - like a finger - that can be easily removed with surgery.