"The" Question

I haven't made it a secret that my daughters are the result of a successful IVF. At least I don't think I've made it a secret. It's not like I bring it up in every post, but I do bring it up.
Anyway, I always cringe at the questions from strangers, the ones along the lines of "Was it natural?" or "How did that happen?" Usually it's just a Nosey Nelly trying to satisfy her (or his) curiosity. Still, I try to be polite, if somewhat vague, in my answer, because every now and then, the questioner responds with "We're looking into IVF (or another fertility treatment), too."
I never know how to respond to these women, other than an "I'm sorry you're struggling. I wish you much success." A few weeks ago, the pool monitor at our neighborhood pool started drilling me with questions. Right as I was about to become frustrated, she confided that she and her husband have been struggling to conceive for years. She said that while most people likely look at me and feel overwhelmed, she would give anything in the world to be this overwhelmed. Then last week at the dentist, the hygienist poured out all her fertility struggles. This was largely a one-sided conversation, as she was cleaning my teeth for most of it, so my response was mainly "Mmmm hmmm."
I have great one-liners stored up for the annoying "How did you end up with quadruplets?" question, but so far, I can't bring myself to use them. Even the curious are mainly well-intentioned and often don't realize how intrusive their questions can be. Many times they know someone who has twins or triplets and just want to share those stories. It's hard to feel like people are constantly judging me, but at the same time, I want to be able to provide some comfort and hope to those who are struggling.