Do women have a better sense of smell than men?

From my own experience, it seems as if women will pick up a scent much more easily than a man. Is there any biological evidence to this?

I have also heard that women sometimes get fluctuations in their sensitivity to smell when they are on their period or pregnant. Do hormones play some part in this?

Yes. http://news.bbc.co.uk/1/hi/health/1796447.stm

Anecdotal evidence has limited usefulness.

But once in Kentucky I was in the kitchen cleaning and slicing some ramps (a very potent wild-growing onion relative, beloved of certain Appalachian folk). I didn’t notice much of an odor, but Mrs. J. called down from upstairs to find out what had died.
This may be true for dogs as well. Last weekend I had occasion to rescue a garden snake that had gotten wedged in a flower pot, and it exuded some sort of stinky musk. My male spaniel seemed mildly interested in the odor, but the female Labrador was instantly repelled.