[Smokin' Joe]

Where the article said "This drop occurred in tandem with steep declines in the abortion rate.".

Either they are more effectively using contraception or they are having less sex.

[Fai Mao]

“Either they are more effectively using contraception or they are having less sex.”

Or both, the two are not mutually exclusive. They could also be having less sex. All three are possible at the same time.