Unless he grew that hair himself, I don't think he has the right to tell you what to do with it.
You're the one that has to take care of it...and being pregnant to boot? It's going to be quite a hassle.
Have you asked your doctor about relaxing while pregnant? It may be a medical necessity to hold off until the baby's born, I just don't know.
Also, think how long it took you to grow your hair out natural to such a lenght...is it worth it to just throw that away? You need to think long and hard, I'd hate to see you regret any decision you make.
Bottom line: Just think about it, and weigh all the pros and cons before you jump into anything.
And while it's nice to take his opinion into consideration, it's still YOUR hair. Shoot, hubby likes long hair so much, let him get a subscription here and grow some himself.