Most professionals agree that climbing during pregnancy is ok as long as the mother is aware of her own body.

(This is rope climbing-not bouldering! Do not do a sport that involves falling off walls.)

As the belly starts to protrude in later trimesters, there is increased risk of trauma to the foetus in terms of harness pressure,  rock fall, or leader fall.

To combat this, you can wear a full-body or specially designed harness that will ride lower across the abdomen rather than directly across the belly button to feel more secure.

Avoid climbing in areas with solid rock and avoid more questionable crags or alpine routes that are notorious for rock fall, slab avalanches, or climbers dropping gear from above and  follow rather than lead.