If my wife wanted to shoot while pregnant, and I couldn't convince her to take the season off, I would build her a moderate thumper like a 7x30 Waters or a 358 Federal, equip the thing with a nice soft, thick trapshooter's (1"+) pad AND a suppressor ... and NO D@MNED BRAKE! Developing tissues are fragile. This is not the time to "toughen" anybody up. Blackpowder, yes; Lazzaroni, no. BPC 45-70, yes. RUM's or Weatherby magnums with brakes, no. I give these only as examples of the direction I would look. The concussion of unmoderated high-intensity cartridges is enough to set my own teeth on edge, and I certainly wouldn't want it for an unborn child. There's plenty of good times ahead with cork-guns and wind-up toy bears, airguns and 22's, 410's, a Superposed 20 and that 7x30 of Mom's. And put a nice soft pad on that 20 while you're at it, and shape that stock to reduce felt recoil. You'd be surprised how little recoil it takes to damage tender young flesh and turn people off from shooting. I sported a blue shoulder every year (and hated the shot) until Dad figured it out.