There's an interesting essay about the coded conversations women have on this issue at _Literary Mama_, in which the author discusses these conversations in terms of "covering" and reckons with her own answers to the twin question.

Here's an excerpt:
"Covering, as defined in the brilliant article by Kenji Yoshino in the January 15 issue of The New York Times Magazine, is what you do when you're not part of a dominant group but don't want to stand out. You don't hide the thing that makes you different –- say being black or gay -– you just keep it from being too obtrusive. If you're one of the hundreds of thousands of women who've had trouble conceiving, you're not alone but you're not in the majority either. And if you've conceived because of fertility treatments, you have not conceived the real way. You have something to cover."

She moves from there to really complicate the notion of "real way" and "natural" for herself and for all women.

http://www.literarymama.com/oped/archives/001014.html

Great article! It's so interesting. I've covered when I'm alone (without the kids) and hanging out with mothers I don't know well. But in front of my children, I never cover because I don't want them to ever pick up in any subtle way that there is anything wrong with how they were conceived. I think kids take those things to heart, and when they hear an omission, they begin to question why Mommy is embarrassed to admit their conception.

We decided that we would never have a day when we sat the kids down and explained A.R.T. We would just talk openly about itand they would always know how they were conceived. It would just be a different path to parenthood rather than a lesser path. So even though they're too young to truly understand, we speak about it whenever it fits into conversation. For instance, my daughter is very interested in babies right now, so we checked out adoption books too and talked about how babies come into your life in different ways.

I can't believe she made that comment about having six. Wait, yes I can.

It amazes me that so many people think twins are just adorable when they occurr from what is essentially an accident or glitch in the natural reproductive process, but then have mixed feelings when they result from effort, determination, and endless hope. Don't both scenarios produce beautiful children that are testament to the miracle of life?

This is a timely post, as I have recently been struggling to decide how to answer this very question. We have four-month old twins, conceived through IVF, and I get the "do twins run in your family?" or "whose side of the family has twins?" (obviously they do not understand that only the maternal side can pass down the tendency to have twins!) constantly. I swear I am going to say "no, but they run in our doctor's office" but I can never get up the nerve to actually say it.
I don't understand why the question bothers me so much- I suppose it is a natural question to ask a mother of twins (and I assume the person asking doesn't mean any harm), but to me it implies that the only acceptable way to have twins is to deserve it by means of lineage.
When we first announced we were pregnant with twins, and the inevitable questions followed, my DH used to say that they do (apparently, somewhere way back on my side of the family there were twins). But I felt that was "covering" and now I simply reply, "No," with a questioning glance meant to ask "why would you ask such a question?"
Today's post gives me the courage to give a more straightforward answer in the hopes that people will think twice about asking such questions, innocent or not.

I know people mean no harm by the question--and most people are taken aback by how snarky I get with it. But it's hard transitioning from being able to go to the grocery store in peace to being accosted with fertility questions just because you're now taking along two babies. Because all these questions do subtly imply that there is a "proper" way to have twins.

My husband looks at the person and says, "no, but like us, they could run in your family with the right drugs." That takes guts :-) I'm more of the lecturing, school-marmish type. Ask me a question and you're going to get a real answer.

I get the twins question all the time -- regarding my two sons who are not only not twins, but not biologically related. :-) Our adopted almost-5 year old is small and developmentally delayed, so he looks 3 1/2 at best. Our biological 3 1/2 year old is ... well, 3 1/2 and on track. *Everyone* assumes they are twins. At first, I corrected people and said one's adopted, etc, etc. Now I just smile, say "no, they're not twins" and leave it at that. I'm not at all ashamed of how my family was formed but not every random Joe in the grocery store needs to know personal details.

As for the 6 kids comment ... my reaction to that was that really, many people don't know about the differences between various forms of ART. For example, you're more likely to get higher-order multiples with, say, IUI than IVF -- but someone who's never been through either isn't going to be able to differentiate. They've just heard that some fertility treatments result in multiples.

When I get the twins comments about whether they run in my family, I say "no - its due to my age". Well, that is true, had I not been 44 when I conceived, I probably wouldn't have done IVF. I also am suprised at the negativity when I do tell someone that we did IVF twice - like we did something wrong. My favs are "well, I never would have done that". To which I answer, well, it was either IVF or no children.