Can sex harm a baby at 29 weeks. lots of quick up and down - will this shake the baby and cause any harm?

Nope, so have fun!: As long as you & your pregnancy are healthy, enjoy sex as often as you want in any position that's comfortable for you. Check out following references that all agree that it's ok to have sex while pregnant in most situations: http://goo.gl/qBs1d8, http://goo.gl/pc1OgI, http://goo.gl/ueETtf, http://goo.gl/Uj0uZw & http://goo.gl/s6yRyr.