The sentence: For decades, Surgeon Generals have warned that

The sentence: For decades, Surgeon Generals have warned that smoking increases the risk of lung diseases, including lung cancer and emphysema, and [can complicate pregnancy, and increases the risk of low birth weight.]

I chose [can complicate pregnancy, increasing the risk of low birth weight]

The right answer according to Kaplan is: [can complicate pregnancy by increasing the risks of low birth weight].
They say "increases the risk of low birth weight should be subordinate to the previous, can complicate pregnancy."

This doesn't make sense to me. "low birth weight" would be product of a complicated pregnancy. "Birth" is after the pregnancy, so it doesn't make sense to say increasing the risk of a low birth weight yields a complicated pregnancy, but you can say a complicated pregnancy can yield a low birth weight. Little help please, because I'm about to burn this stupid Kaplan book!