Senior doctors today called for new regulations on fertility treatment in order to cut the number of premature births.

Assisted conception that involves transferring multiple embryos into a patient's womb should be limited as it increases the risk of babies being miscarried or born prematurely, according to two obstetricians from King's College London School of Medicine.

The proposal is one of several measures to reduce the rising number of premature births that Andrew Shennan, professor of obstetrics, and consultant obstetrician Susan Bewley put forward in the latest British Medical Journal (BMJ).

The obstetricians expressed concern at rising rates of premature birth across Europe, warning that the trend could have serious financial and social consequences.

"The total health burden of the population will not change unless the number of premature deliveries can be reduced," they said.

They urged doctors to question the wisdom of inducing labour and allowing elective caesareans, both of which processes can be used to deliver babies early.

The obstetricians noted that premature babies often require intensive hospital care, and have lifelong health problems.

A fifth of babies born before 25 weeks' gestation have severe mental and physical disabilities, while those born earlier than 28 weeks spend 85 times longer in hospital in the first five years of their lives than full-term babies do.

The editorial in the BMJ follows a Danish study published earlier this year showing a 22% increase in Denmark's premature delivery rates between 1995 and 2000.

The researchers found that even among low-risk women aged between 20 and 40 in Denmark, there had been a 51% increase in early deliveries.

Factors known to increase the likelihood of premature birth include being obese or underweight, and smoking. Ethnic origin and social class also play a role.

However, most premature births followed spontaneous labour, in a sequence of events about which knowledge was lacking, the obstetricians said.