The first three months of pregnancy are vital to future fertility
Chemical compounds could play a role in causing unborn boys to have fertility problems in later life.
Edinburgh University researchers claimed a crucial window between eight and 12 weeks of pregnancy determined future reproductive problems.
They believe that exposure to chemicals found in products such as cosmetics during this period may affect later sperm production.
But they stressed there was not yet conclusive proof this was the case.
The research team was led by Professor Richard Sharpe of the Medical Research Council's Human Reproductive Sciences Unit, based in Edinburgh.
During tests on rats, they blocked the action of androgens, which include male sex hormones such as testosterone, for a short period in the womb.
The experiments confirmed that if the hormones are blocked, the animals suffered fertility problems.
Some of the chemicals which can block the hormones are widely used in items such as cosmetics, household fabrics and plastics.
Prof Sharpe said the chemicals may also increase the risk of baby boys developing other reproductive conditions in later life, including testicular cancer.
He added that if women planning on becoming pregnant were anxious about such issues they could avoid putting any cosmetic products on their skin which could then be absorbed into their bodies.
He told BBC Scotland's news website: "There are lots of compounds in perfumes that we know in higher concentrations have the potential to have biological effects, so it is just being ultra safe to say that by avoiding using them your baby isn't at risk.
"If you are planning to become pregnant you should change your lifestyle. Those lifestyle things don't necessarily mean that you are going to cause terrible harm to your baby, but by avoiding them you are going to have a positive effect.
"We would recommend you avoid exposure to chemicals that are present in cosmetics, anything that you put on your body that might then get through your body into your developing baby.
"It is not because we have evidence that these chemicals categorically cause harm to babies, it is only based on experimental studies on animals that suggest it is a possibility."
However, Prof Sharpe said women were exposed to many of the chemicals he was concerned about through many other routes, as they are widespread in the air and in the fabrics of their homes.
He is due to unveil his findings next week at the Simpson Symposium in Edinburgh, a gathering of fertility experts organised by Edinburgh University.
A spokeswoman for the Department for Business, Enterprise and Regulatory Reform said all cosmetics undergo testing and current legislation ensures public safety.
She added: "All cosmetic products including perfume undergo a rigorous safety assessment by manufacturers.
"The government's primary concern is the safety of the public. The current regulations achieve this."