I am thinking about a career change...

can i wrench while pregnant?

You're kidding, right? But just to give an accurate response - sometimes you need to reach and contort your torso in very unnatural positions. I'd like to see you change a master cylinder or an evaporator when you're pregnant. NOT HAPPENING. Or how about standing under a huge diesel truck for an hour that only can be put up in the air so far and then try lifting a 250lb PTO on your shoulder while you're kind of bent over backwards. Or how about changing a water pump while you lay your belly on the radiator support. Not sure why you would even consider that...

would a shop give maternity leave?

Though I am a dad, I got one day. And my *** hat boss was calling me when my wife was in recovery asking me about some car I didn't finish. Working at a dealer especially is essentially working retail. We don't get many holidays. They want production, they don't want to pay you for not being present.

is there a physical requirement to be a transmission builder .....im 4'10" 86lbs. .......do i have enough strentgh to be a good tech/ mechanic without other ppl's help

Could you lift a transmission from the floor to the bench by yourself? It usually takes two of us usually with some effort. Can you torque something at an awkward angle to 200 ft lbs by yourself? You need some decent upper body strength. There are so many things that require physical strength, hard to even start describing them.

Being a builder in itself probably is less strenuous than being an installer but could you step in and disassemble/build 2-3 units a day, test them and make sure they're right before someone else put them in? That's probably what a trans. shop would be looking for. You'd probably need to learn how to get them out and in effectively before they let you start doing bench work.