Pepin was close to finishing her bottle when she boiled over, milk flowing from her mouth like magma, the whole lot of it. So much and so thick that it seemed she might choke, like Jimi Hendrix or the drummer from Spinal Tap. But she sat quietly on my lap as it poured out, as though this was the plan all along. Drink and release.

We might have had something to do with it. Over the weeks, we'd quickly increased her nightly bottle from 55 millileters to 85 to 100. It's not like she had doubled in size, but we pushed it and she didn't object—until she erupted.

We're pushers. We might be for a long time. I can't fold her onesies without realizing how small she is—it's like trying to fold a spiderweb. Recently we wanted some clothes from Patagonia, for next winter, and matched her growth curve to their size chart. At 12 months, she'll just fit their six-month clothes. They don't even make a hat small enough to fit her.

You never forget you have a preemie because you're not allowed to forget. Every doctor's visit she's assigned a percentile on the growth chart, set against her peers. She began in the first percentile, smaller than 99 percent of other newborns. After 11 weeks, she's now up to the third percentile, a difference that in most surveys would fall within the margin of error. She may be one of the tiniest babies her age, or slightly less tiny.

We want her to grow, and yet we want to keep her close, terrified of the germs that could send her back to a hospital it seems we just left. We've only brought her to one gathering of friends so far, and if we hadn't been waiting to exchange some food we might have left after touching another kid's toys and being told, "You should probably wash your hands. He's got a cold." If we stay home, with no other babies to compare her to, we can pretend that everything's normal.

People talk about a fourth trimester, the first few months after childbirth when a baby is mentally still in the womb, still thinking like a fetus. You hunker down, shut out distractions, and pretend in a sense that the baby hasn't even been born. But we might opt for a fifth trimester, or a sixth, even though she's smiling now and rolling over and batting around the doodads on her bouncy chair. We need time. Not for her to catch up, but for us to catch up to her.

(Photos: A little tummy time, for Pepin and for dad.)