This is set sometime in the latter part of 5th season. Think between Sherlock and Grave Danger.
First few chapters are short, primarily for shock/suspense value.
"In the morning I make the biggest decision of my life."
My heart dropped to my knees at her words. Someone had asked her to marry him, and she was seriously considering it.
She swallowed hard and began again, her voice soft. "I'm, um, I'm 36 years old." She looked away from me. This was not going to be good. She wouldn't even look at me. "There are life decisions a woman can't just put off indefinitely. At some point indecision BECOMES a decision, no matter how much you wish that wasn't the case."
She went silent, so I nodded encouragement. "I'm, uh, not in any kind of romantic relationship now, haven't been for a couple of years." Huh? "I realized a couple of months ago that a window of opportunity is going to soon close for me, and I'd never even seriously thought about what that might cost me. I've always wanted children, always thought someday I'd meet someone, get married, you know. But it suddenly hit me just how little time I might have left for that." She looked down at the table. "I went to the doctor. The fertility doctor. I've decided to have a baby, and in the morning I'm going to Dr. Ross's office to pick the father."
A wave of nausea rolled over me as finally understanding hit me like a freight train. Sara wanted a baby. In the morning she'd select her donor, and soon her belly would swell with a baby. Someone else's baby. I shook my head and closed my eyes. "No, Sara. Don't do it."
Her mouth tightened. "I'd hoped you'd understand. Greg, I want this. I WANT a baby. "
I stared at her for a few moments. "Then have one."
"But you just said..."
I shook my head. "Have a baby - but not some stranger's child." I took a deep breath. "Sara, I'm perfectly healthy. I have an IQ of 170 and about as healthy a family history as you could ask for. Past that, I can give your baby something your doctor's Popsicles can't - a daddy."