The ideal is no more than 50%abnormal forms but I have seen alot worse and as you have conceived previously I would suggest that your hubby more than likely has varible samples and others may have a higher level.
My brother had a sperm test in June, he was 75% abnormal but amount of sperm per amount(whatever they measure it in!!!) was slightly higher then average so doctor said to keep trying for a little longer before looking into other options!
July, my sister in law's period didn't arrive and they are now happily 7 weeks pregnant!!