Preface any remarks to him about this with the heightened sense of smell that comes along with pregnancy. Be glad it is just his breath during my third pregnancy my husband smelt like a tater tot to me and not just his breath. His whole person smelled like a tater tot! It made me so sick. Luckily that went away as the pregnancy went along.
Anyway something that has helped me through the years is a mouthwash called Biotene. It has enzymes that help control bacteria all day or all night long. You need to brush your teeth really well (they also make toothpaste) and your tongue as well to get rid of as much bacteria as you can. Then you swish a couple of teaspoons of it for quite a bit longer than normal mouthwash and get it into every nick and cranny before spitting it out.
I suffered from recurrent sinus infections and sinusitis for many years (until I had some corrective surgery done) and my breath no mater what I tried would go bad about an hour after brushing. It was so frustrating. I was the queen of Listerine but nothing worked until I had a dentist recommended this stuff. I had thoroughly brushed and used Listerine every time I brushed. I used it so much that I was essentially causing my gums to recede without any sign of disease. Almost like brushing and disinfecting my gums away.
Anyway there are two kinds of Biotene and it is with the regular mouthwashes it is in a white smaller bottle. Even though it is a little more expensive you use less so it lasts longer.
I would explain the problem of an extra sensitive nose to him due to pregnancy and then use it yourself so you could set a good example. Tell him "heck I offend myself right now" that it is nothing personal. I always joke to my husband that if he is going to kiss me I need to have eaten what he has eaten recently otherwise I just can't stand it. He likes to eat some pretty pungent stuff but even Doritos are enough to turn me off. He has made a game of it and thinks it is very funny but I tell you what I am not going near anything that smells like kippered herring or pickled garlic!
Good luck with your olfactories.