I called her the Fetus Lost in Space. Because she would throw her tiny head back, eyes closed, and wave her arms as though swimming through zero gravity. And because she wasn't supposed to be born yet.

Pepin has introduced Lucy and I to the concept of "adjusted age," which is simple enough: Premature babies will supposedly be behind their full-term peers for at least two years—milestones will take longer to reach—so to see how they stack up you subtract those extra weeks or months before their due date. Which means that a couple days ago, when we finally hit that date the OB gave us months ago, Pepin turned zero.

These past four and a half weeks—didn't count. They were preamble, preseason. Negative time.

I know there's sound reasoning behind this. And I know that Pepin, barring some superpower granted to her by the Diaper Genie (or what else is it for?), will likely lag. Put her next to a full-term baby born today and she'd still be smaller than almost all of them, despite already accomplishing much more than they ever have. For all her prolific pooping, eating, and sleeping, she only recently rose to meet the growth curve at its lowest point, like joining a flock of geese at the tail end of the V.

But I can't help thinking that these past few weeks have been a kind of internship for her, a study abroad program for fetuses ("Travel outside the womb!"). Surely this on-the-job training hasn't been wasted. You're telling me that my kid's been smashing rocks for her supper and Rotundo over here falls out of the sky and already can do everything better?

Life begins unfair, and we're always surprised that it remains so. But that's not always what matters. Pepin's first few weeks weren't lost time. She was here. She broke us in. She broke our hearts. And if she didn't look like a baby or act like a baby—her limbs were chicken wings, her skin was covered with the fuzz of an old man's back—it's because she wasn't. She was a rare glimpse of something usually closed off, in utero.

On her due date, she seemed for the first time to look familiar, like the photos in magazines that now seem as crudely aspirational as the supermarket rags—Cosmo for the meconium set—with the doughy arms of an aging wrestler, the jowls of Chris Christie. Her eyes move in tandem, her skin is no longer so transparent that you could see the web of blood beneath it. If she was lost in space before, she seems to have landed.

Whatever happens after zero, we'll always have those extra weeks, when a window accidentally opened in the middle of the night and Pepin crawled through, and we hung out like outlaws on stolen time.

(Photo: Pepin, silent-movie style, a few days before her due date. Someday she'll ask why the card didn't just say "one month" and we won't have a good answer.)