Not much to go on, sorry...
It had a brightish blue cover.
No idea of author or title, but either the husband or the baby was called Stephen/Steven, think it might actually have been the baby. Don't think the marriage was great. The mother suffers with intense loneliness and depression pnd after the birth, husband not very supportive or maybe doesn't understand... but eventually she finds something that interests her, can't remember what, maybe she starts to study, and starts to feel more human again. She starts going out and about with the pram, and also getting into her subject, she sometimes reads on a bench in the park. One day when she's doing this, very absorbed, the unthinkable happens and her child drowns in the pond.
She blames herself. Her husband blames her.
Very grim and sad, I read it when I'd just given birth to my first child 
I've looked for it often, without success and I'd be so grateful if anyone recognises it.
Thanks 