This isn't the dark ages, and being pregnant isn't something to be ashamed of. If she wanted to keep it quiet she wouldn't be performing past the initial three months - and I'd put good money on her being well past that stage.
This is a forum about theatre, and I see no issue in discussing how we might not be seeing one of the most promising stars on stage for a while due to a moment of personal happiness. As I mentioned earlier, it would most likely mean she'll be ready to return to the stage around the time of the rumoured tour, meaning its something on topic anyway.
The issue is that people are discussing this online - which basically means, it's being discussed publically. People aren't just speculating either - some are saying she is pregnant as if it's an established fact, when no public announcement has been made by Rachel.
Incidentally, I'm fully aware that this isn't the dark ages and pregnancy isn't something to be ashamed of. However, many women choose to wait until they've passed the first three months to announce the good news, because that's the period when miscarriages are most likely to occur. Also, at the end of the day, it should be up to Rachel and her husband to announce any pregnancy, not random people on the internet!