I was 41 years old, and I thought I was done with having babies. My husband and I were raising four children, and we were plenty busy juggling their needs with our jobs. Our older two were entering the teenage years -- Michaela was nearly 14, Zack would soon turn 13 -- and we were getting a sense of how overwhelming that could be. Elsa was 7, an independent and interesting but high-maintenance child.

But at least there was a light at the end of the tunnel: Natasha, the baby, was nearly 4. She was well out of diapers and had started preschool, giving me three and a half unheard-of free hours on my days at home. Our life was busy, but it had a manageable feel for the first time in years. I was going to yoga classes, swimming laps twice a week, had taken up sewing, and was doing some volunteer work. My forties, I'd decided, were going to be a new beginning for me, a time when I could finally do some things for myself.

But there it was: the purple line. My period was a little late, and I found an old pregnancy test in the back of my underwear drawer, the one left over from the box of two I'd bought to find out I was pregnant with Natasha. It's expired, I told myself, maybe it's wrong -- but I knew in my heart it wasn't. We'd had one birth-control slipup; I'd been hoping all month that nothing would come of it, but, hey, I'm a doctor. I know that it only takes once.

It was early on a Friday morning, and I needed to go to work. I decided to confirm the test before telling Mark, who was still asleep. Really, I was stalling. I figured he'd be upset also; our house is an old fixer-upper that Mark is steadily renovating, mostly on his own, and he was finally getting time to work on it -- time that would go out the window with a new baby. He, too, was beginning to do things for himself, like taking Tai Chi classes and working out at the gym. Having a baby would throw us back into chaos.

I cried my way to work, bawling on the phone to my best friend. It will be okay, she told me, but I didn't believe her. The sweet lab tech at the health center where I work did a pregnancy test for me; she nodded quietly and pointed at the second blue dot. It was real. My mind was swirling with panic. How would we manage? How would the people at work react to yet another maternity leave? And how would we afford another child?

I wanted to tell Mark in person, but he had left to work the night shift before I got home. I couldn't hold it in. I called him in the ICU at Boston Children's Hospital, where he works, telling him through tears that I was pregnant.

He was quiet. "You don't seem upset," I said. "I can't stop smiling," he said. "Why?" I asked, incredulous. "I'm here, surrounded by so much death and dying," he said, "and my wife, whom I love more than anything in the world, calls and tells me she's pregnant. Why shouldn't I smile?"

In that moment, I fell in love with my husband all over again. He was right, of course. And his response was exactly what I should have known it would be; he's a thoroughly good father and loving husband who has greeted each of my pregnancies with celebration. In that moment, Liam started teaching me.