The environment in which an IVF embryo spends its first few days can have an impact on whether it will go on to be genetically normal, research suggests.
A new study found that chromosomal problems can arise as an embryo starts to divide, with acidity potentially playing a role in creating healthy embryos.
Stuart Lavery, a consultant at Boston Place fertility clinic in London, worked on the research, which involved 2,620 eggs from 363 patients.
Half were exposed to a new type of culture medium used to grow embryos, while the other half were exposed to another type of culture.
After five days, the embryos were analysed and more than 300 underwent genetic testing.
The first culture resulted in 29% of embryos with the normal number of chromosomes, while the other culture had only 16% of embryos with a viable number of chromosomes.
Embryos grown in the second culture were also more likely to result in early miscarriage, which is strongly linked to chromosomal abnormality.
Mr Lavery said the result showed that the environment used to grow embryos could play a crucial role in chromosomal make-up.
He said the culture medium and incubators used in IVF are designed to mimic the conditions in the womb, but the research suggests that the pH levels in the environment may play a role.
He said: "We've known for years that the major impact on chromosomal abnormality is whether you get an abnormal egg or abnormal sperm. That embryo is not going to give you a healthy baby.
"But we also know that even when you get a healthy egg and sperm, as the embryo starts to divide, there can become a problem with how the chromosomes split.
"We've been able to show how important those first few days of life are and how the environment influences it.
"We now need to do more research to find out what it is - whether it's the pH, the humidity, the amino acids in the culture medium or something else.
"Our research suggests that a lower pH seems to be advantageous."
The research is being presented at the British Fertility Society annual conference in Edinburgh.