I'm fairly young (32 years old) and need to have a spinal fusion for damage done to my spine in a car accident years ago. They told me I'll have to use my own bone harvested from the pelvic bone. Evidently, I'm not a candidate for bone graft substitutes because I could get pregnant. What does that have to do with anything?

Bone graft substitutes are made from animal collagen tissue. When used to help promote bone growth, these therapeutic proteins can help speed up the bone formation and healing process. But because they come from outside the body, the immune system may set up a defense against them. This means the body forms antibodies to the proteins.

These antibodies could cause potential harm to a developing fetus. There could be cross-reactivity reactions. The antibodies could cross the placenta (protective barrier between mother and child). Since no studies have been done (or will be done) to see the effect of these antibodies on the in utero (in the uterus) development, these substances cannot be deemed safe during pregnancy.

Even if a woman receiving bone graft substitutes is not pregnant, there's no way to predict whether she might get pregnant while these antibodies are circulating in her system. And we don't have long-term studies yet to show what happens to these antibodies over time. It's possible with the passage of time, there could be delayed adverse effects of this treatment.

So for now, it's easier and safer to say that the use of bone graft substitute is not advised during pregnancy or in women with childbearing ability.