The number of women who give birth to twins or triplets after undergoing IVF treatment looks set to fall.
The changes are due to come into effect in March
The Human Fertilisation & Embryology Authority, which regulates IVF in the UK, has published guidelines aimed at cutting the number of multiple births.
From March, women under the age of 40 will have two instead of three embryos implanted as part of their treatment.
The move follows a string of studies showing multiple births are a risk for mothers and their babies.
Over half of babies born as a result of fertility treatment are twins or triplets.
Under the new rules, doctors will only be able to implant three embryos in any one treatment cycle in "exceptional circumstances".
However, this rule will be relaxed for women over the age of 40, who have a lower chance of conceiving.
In a report, the HFEA said the changes would not reduce a woman's chances of having a baby.
"Research has shown that limiting the number of eggs or embryos transferred during treatment to two reduces the number of multiple pregnancies without causing a significant decrease in overall pregnancy rate," it says.
The report, called Avoiding Multiple Births, says multiple births are a real risk for mothers and their babies.
It says women expecting more than one baby are more likely to suffer pre-eclampsia or dangerously high blood pressure.
Babies are more likely to be born prematurely and are at increased risk of dying.
It says multiple births can also put pressure on parents.
"Caring for more than one baby at the same time can cause emotional, practical and financial stresses for families and this may place additional strain on relationships," it says.
The report says the risks are so great women facing a multiple pregnancy may wish to abort one of the babies "in the early weeks".
"This procedure is carried out to give the remaining foetuses a better chance to develop into healthy babies," it states.
Suzi Leather, chair of the HFEA, said the guidelines aimed to bring IVF births more in line with natural ones.
"Women are designed to have healthy babies, one at a time, and with natural conception this is what usually happens.
"But over half of babies born as a result of fertility treatment are twins or triplets.
"The aim of the HFEA is to bring the number of multiple births from fertility treatment closer to that which occurs naturally."
However, Dr Mohammed Taranissi , director of the Assisted Reproduction and Gynaecology Centre in London, told the BBC he would consider flouting the new rules.
"This is not a law. These are only guidelines. If I believe honestly that this is not in the best interest of patients I will do what I think is fit," he said.
But Professor Allan Templeton, honorary secretary of the Royal College of Obstetricians and Gynaecologists, backed the move.
"Every attempt should be made to avoid multiple births, particularly triplets, following IVF treatment."
Professor Alison Murdoch, chair of the British Fertility Society, also voiced her support.
"The British Fertility Society wants to see health women and healthy babies, and this is best achieved by avoiding multiple pregnancies."
Jane Denton, director of the Multiple Births Foundation and a member of the HFEA, welcomed the change.
"For some patients the prospect of twins or triplets may seem an ideal way to have the family they long for. But the reality can be very different," she said.