Super rude question?

Megan
I was out at a restaurant earlier and my husband and brother were talking to a couple at the bar - people we have never met before. I walked up to them and the woman asked me when I was due. I told her October 2, but most likely mid-September because we are having twins. Her first response was, "oh, was it natural?"
I was totally caught off guard and just responded no, it was a long road for us to get here. Afterwards I was completely pissed and thought it was so incredibly rude for her to ask. How is that any of your business how I conceived my children?? 
Now I'm thinking I need some sort of standard response for people/questions like this that will put someone in their place without being too rude. Am I overreacting?