For overweight women looking forward to becoming a mum, here's some bad news: a new study has shown that obese women are as much as 28 percent less likely to become pregnant and have a successful pregnancy.

The study, conducted by Barbara Luke, a researcher in the Michigan State University College of Human Medicine's Department of Obstetrics, Gynecology and Reproductive Biology, focused on data of nearly 50,000 women using assisted reproductive technology.

The results showed that women who are simply overweight have a 14 percent less chance of a successful pregnancy.

"The results are not surprising; obesity is a state of inflammation and is not a good environment for conception or foetal development. The key message is to lose weight, prior to conception, and focus on pre-conception health issues. Once you become pregnant, the baby is developing in that environment," Luke said.

As part of the research, Luke's team looked at the effect increasing body mass index had on a woman's ability to become pregnant using assisted reproductive technology and how obesity affects pregnancy outcomes.

They compared outcomes to women with normal body mass index (BMI of 18.5-24.9). Women were classified as overweight (BMI of 25 to 29.9), Class 1 obesity (30-34.9), Class 2 (35-39.9) and Class 3 (40 or greater).

They found that women at Class 3 obesity were 35 percent less likely to become pregnant; Class 2 resulted in a 28 percent less chance; 9 percent for Class 1; and 3 percent for overweight women.