WASHINGTON (Reuters) -- The Caesarean delivery rate for U.S. women hit a record high in 2005, spiking by nearly 50 percent in a decade, while teen births fell to a new low and births by unmarried mothers rose, according to a new government data.

Close to a third of all babies born in the United States -- 30.2 percent in 2005, up from 29.1 in 2004 -- were delivered surgically in a procedure also commonly called a C-section.

This marks a 46 percent increase in the Caesarean delivery rate since 1996 and continues an upward trend dating back three decades, according to the Centers for Disease Control and Prevention's National Center for Health Statistics, or NCHS.

The rate stood at about 5 percent in 1970. C-sections are favored when doctors believe vaginal delivery could cause medical complications, but have become more and more commonplace for what would be considered normal births.

The increase comes amid a controversy over whether some women are opting for medically unnecessary C-sections out of convenience and whether some doctors are performing them because they fear being sued if they do not.

While in the past older mothers were more likely to have a C-section, NCHS statistician Fay Menacker said Caesarean deliveries were increasing for women of all ages and races.

The World Health Organization has recommended C-section rates no higher than 15 percent of births.