Fibroids can grow rapidly so your yoga practice should focus on softening and opening the abdominal area. It might be tempting to do so, but guard against letting the stomach hang out or tilting the pelvis forward – this simply encourages the abdominals to become weak and puts strain on the lower back.
Avoid poses that put pressure on the abdominal area, such as deep twists, strong backward or forward bends. Twists such as Bharadvajasana and Parivrtta Janu Sirsasana can be beneficial hopwever, because they allow the abdominal area to be in an open position.
As fibroids grow, your practice should be changed to accommodate them. As a guide, read carefully the instructions from Geeta Iyengar on how to practice for Endometriosis. Women with large, heavy fibroids should approach yoga as if they were pregnant and include supported poses like Supta Virasana, Supta Baddha Konasana, and Salamba Setu Bandha Sarvangasana (from a chair).
With gratitude and thanks to Geeta S Iyengar.
Iyengar Yoga Teaching & Training 