Hello, I have gone through your query. While the submucous fibroids carry the maximum risk of causing an abortion, secondary to the submucous variety, subserosal fibroids are rare to cause complications in pregnancy unless they are large enough. If you have a retroverted uterus and hence the posterior fibroid is pressing on the growing uterus, postural treatment can be somewhat helpful. If the sac is getting distorted as has been shown in your case, myomectomy may have to be contemplated to save the pregnancy. This should be managed in expert hands so as not to disturb the existing pregnancy. Uterine artery embolization may not be suggested in view of an active pregnancy. Hope you find this information helpful. Take care.