There are just a few details I recall from a novel I read about 25 years ago.
The setting is a fairly unmemorable future space-faring society. I don't recall any major character aliens, but that doesn't mean there weren't any. The 2 main characters of the novel were an unmodified human woman from Earth, and a man from a rather more hostile world settled as part of the expansion of humanity into space. I believe they were law-enforcement types, or at least on a mission on behalf of some law-enforcement organization.
His planet is mostly cold, possibly heavy gravity, and he is bigger and stronger than stock humans. At a critical point in the novel they are somewhere hot, and he appears to suffer a seizure (to the woman's distress). But he gets up and reveals that on his homeworld there is a very short period (something like 2 weeks) when his planet warms up and is very fertile. In that period it is important for his people to be active the entire time to store as much food as possible, so they have been modified to enter a special state for that period when they are stronger, faster and don't sleep.
The woman explains how all the unmodified humans on Earth have an inferiority complex toward all the other tweaked/improved humans from the colonies, and the man counters that all the modified humans envy the stock humans. She can have a child with little to no concern, but on his world - because of the modifications - having a child is a big gamble. A large percentage of babies are simply not viable, and even if the baby survives, bearing it has a significant chance of killing the mother.
His name might have been Bram?
