The Birth Defects Foundation (BDF) suggests certain types of abnormalities have increased by up to 50% over that time.

The BDF estimates one in 16 of all births results in neonatal abnormalities such as cleft palates of malformations of the hands and feet, around six times higher than official figures report.

The charity says this could be because they count all birth defects, rather than just the most severe, some defects may not become apparent for some time, and because official statistics rely on a voluntary system of reporting.

The charity is launching a campaign on Monday to spell out a five-point plan to give mothers a better chance of having a healthy baby.

The plan will cover family medical history, taking folic acid supplements, reducing alcohol, stopping smoking and eating a balanced diet.

Oestrogen link

The occurrence of some birth defects has declined, but the BDF has shown a sharp rise in three specific defects; cleft lip or palate, gastroschisis (abnormality of the abdominal wall) and hypospadias (a condition affecting boys in which the opening of the penis is situated on the underside of the shaft).

Why there has been a rise in certain types of defects is not clear, but long-term use of recreational drugs by young mothers and an increase in oestrogen-like substances in diets are possible explanations.

Research for the BDF suggests the incidence of cleft lip or palate, which can require a number of operations to repair, had increased from 5.8 cases per 10,000 births in 1995 to 9.2 cases in 1999.

Hypospadias has risen from 7.5 cases per 10,000 to 8.5.

Gastroschisis, a weakness in the abdominal wall that leaves the intestines protruding at birth, has risen from 1.3 to 1.9.

The condition has been rising in both the UK and the US and is five times more common in teenage mothers than other age groups.

Professor Michael Patton, medical director of the BDF and head of medical genetics at St George's Hospital, Tooting, London, told BBC News Online said there were theories, though no proof, for why these relatively rare conditions were being seen more frequently.

He said: "With hypospadias, it is just possible there could be an environmental effect, possibly with an oestrogen-like effect in the environment. That would be a potential theory, but we haven't done a study that proves it."

Other experts have made a link between hypospadias and the fertility technique intracytoplasmic sperm injection.

Professor Patton added: "Gastroschisis has always been a relatively rare abnormality. But there seems to have been an increase amongst younger mothers in urban areas.

Practical planning

"We don't have any positive proof, but there has been a suggestion that the wider use of a mixture of recreational drugs could be behind that increase."

One success story highlighted by Professor Patton is the decrease in incidence of spina bifida, which has fallen by two thirds in women at high risk because they have a family history of the condition.

Folic acid, known to help prevent spina bifida and other neural tube defects (NTDs), us now given to all pregnant women.

Sheila Brown, chief executive of the BDF, told BBC News Online it was important prospective parents were aware of family medical history of conditions such as congenital heart malformation, so they could make practical plans like having the baby in hospital rather than at home.

She added: "We're not saying that all birth defects are caused by drinking, smoking or street drugs. But we are saying, if you want to give your child the best chance in life, then you can by following the points in the plan."