05/16/2012 10:15 am ET Updated Jul 16, 2012

Oh, Baby: What to Expect When You're Expecting a Movie

Re: Cameron Diaz's breasts.

It wasn't exactly an average subject line, never mind an average subject -- even for someone who spends a fair amount of time talking about breasts (swollen, tender, and otherwise pregnant or lactating, that is).

But there it was, sitting in my morning inbox, making a lot more sense than I ever could have expected. At least, once I opened it -- an email sent by the producer and director of What To Expect When You're Expecting, the movie, asking about how much Cameron's character's breasts might grow from their prepregnancy size by the beginning of her second trimester.

Talk about what I didn't expect when I delivered the proposal for What to Expect When You're Expecting -- true story, two hours before I went into labor with Emma -- a very young, very naive, and very clueless first time expectant mom determined to write a pregnancy guide that would help even a handful of other expectant parents sleep better at night than I had and my husband Erik had.

Fast (and I mean fast) forward 29 years later, and I was consulting on Cameron's breast size, running checks on Elizabeth Banks' pregnancy symptoms, advising on Ben Falcone's Couvade Syndrome, checking out prosthetic bellies and ultrasound images.

Not exactly my day job (which, by the way, I love so much it makes me weak-kneed to think about it), but then again, helping What to Expect When You're Expecting make the unlikely transformation from how to pregnancy guide with one character (you, the expectant parent) into a romantic comedy with an all-star cast of many, has been unexpected right from the start.

Most unexpected was that I said yes to the pitch from Phoenix Pictures in the first place (I had already said no to a Hollywood film several times before). Of course, me being me, it was a yes... but. Yes, but the movie would have to be true to the sensibility of What to Expect (warm, relatable, funny as appropriate, real as possible, sweet but not insipid, sensitive but not sappy). Yes, but it would have to capture as many stories as possible, so it reflected some of the different ways that couples become parents, but also the emotional connection, the fundamentally human and universal bond that parents share. Yes, but you will have to deal with one very protective mom... me.

A ridiculously short time later, Erik and I were executive producers on a major motion picture green-lit by Lionsgate, and we were watching a cast come together that was so insanely talented, so beautiful to look at, that we felt like kids in a candy shop who had just ended up with a huge bag of the really good stuff (not a sucker in the bunch).

Barely a month later, in August, we were sweltering in Atlanta's Piedmont Park, laughing ourselves silly as Chris Rock led his merry band of bros (aka The Dudes Group) through take after take of side-splitting improv. Talking to the adorable Matthew Morrison about what it's like to have a father who's a midwife (really). Watching Jennifer Lopez calm a crying four-month-old like only a mama could, a crew of set designers turn an empty storefront into a fictional store for breastfeeding moms (The Breast Choice), Dennis Quaid and Ben Falcone race golf carts, and Elizabeth Banks rage against the unfairness of her hormones in a very public mega mommy meltdown. Hugging anyone who would hug back (and they all did). And yes, sitting by the side of a very pregnant extra who went into labor in -- you can't make this stuff up -- the very last hours of filming (she's now the mom of a beautiful 7-month old boy named Shay, who I get frequent fixes of on Facebook).

It's now mid May, opening day is in less than a week, and in the midst of a movie media storm, I'm not going to lie... I am one nervous mama. I spend my nights doing my day job... and greedily catching up with my moms on Facebook and Twitter until Erik drags me (or if that fails, carries me) to bed. Nine months from when the day filming began, our newest baby will be delivered. Is it perfect? No baby, like no parent, is. Did the experience of making a movie, like making a baby, give me heartburn? At times. Am I happy? More than I could have ever expected.