Is it legal to be turned down for a promotion because "you're too focused on your baby"?

My husband and I are expected our 1st child in just a few months. He was recently encouraged to apply for a promotion at his company and today, he found out he didn't receive the promotion. That didn't necessarily surprise us, but what did surprise us is that his superior told him the reason he didn't get the promotion is that "he's too focused on the baby". Those were his manager's exact words. Is that even legal? Obviously my husband has every intention at finding a new position at a different company ASAP, but he and I had never heard of anything so ridiculous.