Health officials are trying to determine why Calgary has a growing rate of premature and low birth weight babies.

Premature babies accounted for 9.3 per cent of births in 2004. That's up from 8 per cent in 1999. Meanwhile, low weight babies accounted for 7.1 per cent of births, up from 6.3 per cent during the same time period.

Researchers from all over the world will gather in Calgary for a conference in May to help determine why this is happening and how to curb the problem.

Jodean Harrison's nine-month-old son Max was born premature. Harrison was 35, healthy and a non-smoker when her water broke on the way home from a camping trip.

"I was immediately just mad, because I'm like, this can't happen. At 34 weeks their lungs aren't developed yet. They're not ready. They can have problems. He's going to have preemie issues."

Max ended up staying in a special care nursery for 13 days before going home.

Doctors and researchers in Calgary are trying to piece together just why so many women like Harrison are giving birth to smaller and premature babies.

Suzanne Tough wrote a report on the issue for the Calgary Health Region. She said one factor is that women here are waiting longer to become mothers.

"Almost 20 per cent of women are over the age of 35 when they're having children, and that is higher certainly than other urban centres."

There are also regional differences within the city. 

Tough said there are higher rates of premature and underweight babies in Calgary's northeast.

"We see higher rates of low birth weight in our lower-income neighbourhoods, where we also often have fewer physicians providing services [and] where we have more Calgarians with English as a second language who may not know how to access services in our city."