If she were also from his time, he'd be straight-up insulted. Only barbarians, or the sort of scum one doesn't want to meet in a dark alley, would loose the threat of an unwanted pregnancy on their partner.

But she isn't from his time. And he knows full well things weren't like they are for his now. (It's one of his favorite rants)

"There is. Injections, actually - most of the crew is on it, for shore leave." His voice is dry as the Vulcan deserts.

He pauses, his head bowed over the sink, twisting the towel in his hands.
"I went the more old-fashioned way." Every medication has risks of failure. After losing Joanna, he couldn't emotionally afford more of those risks.