More Canadian babies are entering the world in difficult circumstances — underweight and through caesarean sections, says a new report on birthing trends from the Canadian Institute for Health Information.

The number of babies born underweight has been increasing steadily over the past five years, the report says. It shows that in 2005-06, about one in 16 babies, or 6.1 per cent, born in Canadian hospitals weighed less than 2,500 grams (5.5 pounds). In 2001-02, low birth weight babies accounted for 5.7 per cent of hospital births.

The CIHI report, Giving Birth in Canada: Regional Trends From 2001-2002 to 2005-2006, highlights key differences in the rates of low birth weight babies across the country.

Prince Edward Island and Manitoba had the lowest rates of underweight babies (5.0 per cent and 5.4 per cent respectively) in 2005-2006, while Alberta and Ontario had the highest (6.9 per cent and 6.4 per cent respectively).

"Some babies weighing less than 5½ pounds at birth may have difficulties ahead," said Caroline Heick, CIHI's director of information services. "For example, they may face long periods of hospitalization and have an increased risk of lifelong complications."

Dr. Vyta Senikas, executive vice-president of the Society of Obstetricians and Gynaecologists of Canada, told CBC News that those complications can include lack of lung development, an increased risk of brain hemorrhage and further health problems later on.

She says that several factors are driving the low birth weight trend, with premature infants responsible for most low birth weights. Women are getting pregnant at older ages, which increases the chances of health problems during pregnancy. Older women are also more likely to undergo fertility treatments, which can lead to multiple births and babies that are often premature and underweight.

Heick is particularly concerned with the increase given what she describes as "years of progress" in prenatal care — including more education aimed at women concerning diet, exercise and other good health practices during pregnancy.

The report also finds that the number of women giving birth by C-section in Canada has risen over the past five years, to 26 per cent in 2005-06 from 23 per cent in 2001-02. Though it is lower than the 29 per cent rate in the United States and Australia, it is higher than England's rate of 24 per cent.

CIHI's analysis found that women who had undergone a previous caesarean section had an 82 per cent chance of having a second one, up from 73 per cent in 2001-02.

Heick says that increasing obesity levels among women are resulting in more C-sections, as obesity can lead to dangerous pregnancy complications that require emergency surgery. She also says changing hospital practices are increasing surgical rates. "More obstetrical interventions are becoming accepted," she told CBC News.

Women having C-sections are on average slightly older than those delivering vaginally, the study indicated.

The World Health Organization recommends that no more than 15 per cent of all births should involve a caesarean section.