I've been shearing my ewes when they start forming an udder and their vulvas swell...I haven't had any birthing problems yet, except for 2 lincolns that lambed that possibly had problems, but I hadn't even sheared them yet. I find it easier for me as a beginning shearer to shear when they are swollen with lambs so that there aren't as many folds in their skin. I'm sit them up on their rump carefully (not just plop them down), and not hold them there for very long, but I haven't had a birthing problem because of shearing and I haven't had any sheep with problems from the stress of shearing so close to lambing. I'll probably do my ewes that are due April 15 around April 1.
Leah