You dont need to worry about having any Lewd score to get the "good true ending".. just.. dont slut it up. You can refuse everything as long as you avoid getting naked as much as possible and dont loose to bosses/major fights, and turn down every other option. You can have max Lewd and still only go for Luis/Lewis. Gets you the "best happy" ending technically.
And as for pregnancy.. yea.. i have no idea what the chances are for it.....but.. to birth you have to go to the snow hut north of the "Sacred town". But.. when preg kicks in.. no idea.. i dont even think its possible until you get to the point of hunting down the 4 gates, or if its locked until you get the convo about babies.
I will say for anyone having issues or want to semi-rush-tweak the game... go find the rpg save editor (available on this site) to edit your save games. Money, Stats, Items, and if you want to get dangerous editing Flags, Switches and Variables. Want all the spells?.. give yourself 1-3 of every magic book.. use .. have fun. (course i did that and ended up barely using them as later weapons in the game even without much ATK power editing is overpowered). Theres also the "stat" beans that exist in the game that you can give yourself a stack of and use to your hearts content. I did that at least to get thousands of MP available and use whatever Special Power I wanted and also ignored most the magic spells in the game. You can edit Lewd points and Lewd level if you want (but i believe in the CG viewer you can spike that level up or down even without having finished the game yet, unlike other status changes available in the CG viewer that require you finish the game once and/or get the "best" ending). Theres more avail for editing, but you risk breaking your save if you mess with something you shouldnt and/or go too far.