As Shane noted, if this is an issue being taken into legal dispute, then you would be best served by consulting an attorney. I believe most attorneys will tell you that there is always recourse, it's just a matter of how much money and effort you are willing to spend to pursue it.
I suspect that you have thrown your question out to the community to find out if there has been any precedent set in previous cases on which to determine whether it would be worth your effort to pursue this matter.
Some other questions you may wish to pursue are ... how "leaded" is the property? The LL is legally obligated to delead the property upon the birth of the baby AND obligated to house the tenant if displaced during the deleading process. The LL can not back out of the lease just because the tenant discovered she was pregnant. That would violate MCAD laws. A real estate professional can NOT lease out a leaded property to a tenant with a child under the age of 7. Seems to me that these would all factor into the case as well.