Official Poser scale is 8.6' in one Poser unit. Figure designers tend to scale their figures at 8' to a Poser unit, so when you use the 100% scale export your figure in MD will be 8.6/8 = 1.075 times too large. Now this does not sound serious, but a female figure intended to be an average 1.68 m tall becomes 1.075*1.68 = 1.81 m tall.

This does not matter as long as you just use MD to make clothes 'as fitted'. However if you work to real life examples fom for example Burdastyle you suddenly need to scale the patterns.  

I suggest therefore to use export from Poser at a slightly reduced scale of 93%, and fit the clothes to that. Then if you choose the 1 Poser unit = 8'  export scale, you will get a nice fit. If you used a full scale avatar, you will need to use the 8.6' export scale.