BAKERSFIELD, Calif. -- To a developing baby, just a few extra weeks in the womb can make a big difference.

Infants born even two or three weeks early are more likely to have breathing problems, brain injuries, and other health issues that put them at higher risk for intensive care and death within the first year of life.

A new government study by the National Center for Health Statistics found the rate of these so-called "late preterm" births -- babies born between 34 and 36 weeks gestation -- has increased by 20 percent.

Currently, more than 300,000 late preterm babies are born each year.

Many factors contribute to the problem, but the researchers said doctors are increasingly causing premature births by inducing labor early or delivering the baby by C-section.

While sometimes pregnancy complications necessitate a premature delivery, many experts are concerned about early convenience births that take place because of the mother's preference or a doctor's vacation schedule.

The studies are clear: Babies who remain in the womb until they are full-term enjoy the healthiest start to life.