They don't have lungs at three months do they?
By three months the lung tissue has differentiated and begun to develop, but they aren't complete. By three months most tissues have differentiated, but they aren't nearly done developing and thus aren't ready to function. A baby born at three months absolutely would not survive without medical intervention (and likely even then, I think the record is somewhere around 4.5 gestation)
no matter what the environment was like. Unless the environment can regulate the babies' sodium, potassium, calcium, blood pH, blood glucose, blood volume, cardiac output, liver function, respiratory function, etc. etc. the baby would die.
What would you say the minimum gestation would be for viablity? (assuming a perfect envioronment)
It just depends on the fetus. If you define viability as a 50% chance of survival (as it usually is), the minimum with intensive medical intervention is about 24 weeks. Without intervention the minimum is
probably somewhere around 8 or 9 months--which is why this is the typical term (think in evolutionary context). A baby is considered premature if it's born before 37 weeks, and premature babies usually require some form of medical intervention. I haven't taken obstetrics yet, so what I know has been gathered from other courses which have mentioned it. I've taken embryology 1, but I still have embryo 2 and 3 to go. In other words, I could be wrong.