I understand your concern.
The fusion operation before pregnancy
does not affect growth/development of fetus.
The problems to the mother in pregnancy depend on the gap between fusion operation & pregnancy,I am afraid you have conceived a bit earlier after your surgery. It's hardly 6 months gap--You may have to face -
- pain in lower back and also sacroiliac joint
- the spine being immobilized, the stress
on spine is distributed to adjoining sacroiliac joints( which are more movable due to pregnancy)
- You may not get the benefit of sub dural anesthesia
while in labor pains.
- during delivery more stress is put on coccyx ,so you may have chronic pain
in the joint after delivery.
* From this point of view a combined opinion/management by your surgeon & gynecologist would help you.