Was your T actually pregnant at the time you started seeing her? If so, yes, she should have let you know. If not, how exactly do you expect her to predict such a thing? Even if she planned on getting pregnant, there was no knowing she would actually get pregnant, how long it would take to get pregnant, even if she'd be able to get pregnant even though she had other children. Even if she's had children before, it doesn't always work out quite the same the next time around. These things, as much as we'd like to think they are entirely predictable, just aren't, even for the people getting pregnant. My first time I got pregnant practically the moment I thought about it. The second time took quite a long time. Just no way to really know.

She has no obligation to let you know she is planning to try to get pregnant. That's her personal business and her medical business which she has a right to keep private. If this is such an issue for you, don't see female therapists. But male therapists can take family leave too. Or they can have medical issues that crop up. People have life events that can pull them away from their jobs for fairly long periods of time. They get ill. Family members get ill. Parents age and need tending. These events are part of life. No professional can guarantee that nothing will happen to call them away for even long periods of time.