1. Absolutely would not have taken her anywhere alone. Even if you're not accused of anything, you're now in custody of a minor, with no prior agreement or knowledge from the child's parent(s) or guardian, and this opens up a huge legal chasm under you. 

2. I would want to hear how she ended on on my particular doorstep at 0325, expecting me to a) answer the door, and b) get up, get dressed, and then take her somewhere.

3. Would certainly have called 911 and asked dispatch two things: a) I want a record made of my description of the circumstances, time, her request, etc, and b) I want the FD to dispatch a EMT/medic to my location to look the girl over for evidence of abuse, sex trafficking, etc. I'd be especially suspicious of the latter, given that you thought she might be pregnant. 

Back in the late 80's, when I lived in Southern California, I had a child of about 10 years old show up on my doorstep after midnight, asking for the same sort of thing: a ride somewhere. I refused. There were hundreds of condo's in the development; how did this kid end up on my doorstep, on the second story, at this time, out of all the other units he could have asked?

Later, I learned that there was someone burglarizing condo's in my development. They already knew from scoping out the development during the day how many people lived in a unit, and who they could try to rob if only one person left to drive the child somewhere. Then they'd send in the kid, asking to be driven to an address that was hard to get to in the dark to buy time. 

Recently, I've seen a guy here in Wyoming who stopped to help a young woman, only to be accused of sexual assault, and then have her later recant when interviewed under oath. He was smart enough to have his cell phone recording the audio of him taking her somewhere, and when the police heard that, they became more skeptical of the woman's claims and re-interviewed her. He had no charges brought, but in the meantime, he spent thousands on retaining a lawyer. 

My experience as a first responder has hardened any instincts I might have had to help people as "just a good citizen."