Hi Lee-Ann,
I just scanned a government release document on the effects of ammonia exposure, and there is no evidence that ammonia passes through the placenta from mother to baby. There is some evidence of cows being subjected where the calf was a little smaller than normal, but in these cases the health of the mother was also affected.
If you have suffered nothing more than a headache from the fumes and were ok after that, I think it's safe to assume that your baby is perfectly fine and unaffected.

Kerrie