Hawai'i's abortion rate continued its downward trend of recent years, although the rate remains above the national average, with slightly more than one in every five pregnancies being terminated voluntarily here.

That's the finding of a new national study on abortions by the New York-based Guttmacher Institute. "Abortion in the United States" shows abortion is declining in the nation as a whole, though trends vary significantly among states. The institute said of the 27,400 women in Hawai'i who became pregnant in 2005, 20 percent induced abortions.

The institute also reported there were 21.8 abortions in Hawai'i per 1,000 women between ages 15 and 44 in 2005.

That's down from the rate of 22.2 in 2000, but still was high enough to rank Hawai'i 12th highest in the nation, the study data showed.

Abortion remains a polarizing social issue, evoking passionate arguments on both sides. Hawai'i hasn't adopted major abortion restrictions like those of other states such as waiting periods, mandated parental involvement or limitations on public funding for abortions, the report noted.

It also said the long-term trend toward fewer abortions continues. In 2005, the national rate fell to 19.4 per 1,000 women, the lowest level since 1974. That was the year after the Supreme Court legalized abortion nationwide.

The study's authors said more work is needed to determine the exact cause of the recent decline.

But writing in a health journal, the authors said the reasons "likely include a range of circumstances, such as better contraceptive use, lower levels of unintended pregnancy, more women carrying unintended pregnancies to term and greater difficulties accessing abortion services in some geographic areas."

One factor in Hawai'i's decline may be the shrinking number of abortion providers in the state.

The report noted Hawai'i had fewer physicians performing or reporting performing abortions.

The number of providers here fell to 39 in 2005, which was about one-quarter less than the number in 2000.

At the same time, there's also been a rise in the number of unmarried mothers giving birth. State Health Department figures show unmarried mothers accounted for 36 percent of babies born in the state in 2005, up from 30 percent a decade earlier.

Other figures reported by the Guttmacher Institute researchers show that fewer Hawai'i women are opting to abort pregnancies compared with 14 years ago.

In 1992, the state's abortion rate was the second highest in the nation at 46.4 per every 1,000 women, trailing only the District of Columbia, which had a rate of 134.6.

Since then, Hawai'i's rate has dropped by more than half.

The national rate fell at less than half of Hawai'i's rate of decline.

The researchers noted the state rate may differ from the rate for state residents because some of the women having abortions here were from other states.

And some Hawai'i residents traveled elsewhere to abort their pregnancies. They noted that about one-quarter of abortions in Delaware in 2003 were obtained by out-of-state residents.

Reach Greg Wiles at gwiles@honoluluadvertiser.com.