ATLANTA — American couples are not as infertile as it might seem.

Despite a boom in the use of fertility treatments, a new government study shows the percentage of married couples having trouble conceiving has dropped slightly in recent years.

About 6 percent of married women under 45 failed to get pregnant after at least a year of sex without contraception, according to the report. That’s down from less than 9 percent some three decades ago.

That may seem surprising given how many women seek help to get pregnant; the use of fertility treatments, including in vitro fertilization, has doubled in the last decade.

But that increase is driven by larger numbers of women trying to have children in their 30s and 40s, when female fertility declines.

So while infertility clinics may be more common and used more — particularly by more affluent women trying to have their first child at older ages — that’s driven by a change in the market, not biology, said Anjani Chandra, lead author of the study.

“This runs counter to what a lot of people think,” said Chandra, a researcher at the Centers for Disease Control and Prevention.

The study released Wednesday focused on married women. It was based on in-person interviews of more than 12,000 women and more than 10,000 men, ages 15 to 44.

The results of the interviews conducted in 2006 through 2010 were compared to four similar surveys done since 1982.

The trend was relatively flat, but overall, there was a slight decline.