Yorky....I'm a CM and have had 3 new starters since I've been 12+ weeks pregnant and overwhelmed by how it hasn't bothered them. They've basically all said that because I'm the one for them, the pregnancy bit they can deal with I'm having 12 weeks off. Just to give you an idea (I'll name the new ones mindees 1-3):
Mindee1 - booked with my in August and paid deposit. I let them know just before Christmas that I was nearly 12 weeks pregnant and felt awful and if they wanted a refund, I'd understand. They told me to not be so stupid, they'll work something out for the 12 weeks and they still wanted me, mindee started in Feb
I took a risk and gave notice to 2 (had reasons) and was worried about filling those spaces. Well....
Mindee2 - 8 week old started 4/5 weeks ago (so now 12/13 weeks). Mum wasn't put off by my pregnancy and 12 weeks off as they are very flexible and run own business blabla. They wanted me so said they'd work round my time off
Mindee3 - 8 month old came for a while and again the mum said she didn't want any of the others she'd seen and could therefore work round my time off. Unfortuntely the poor love was suffering terribly when mummy wasn't there and I decided that for the short time he was coming each week, I wasn't the best person for the job as would take and long time to settle and of course I'm going to be having time off soon.
Anyway, I've got them on my waiting list for when I start back, along with others and I'm overwhelmed by how lovely everyone has been and how the existing parents didn't get annoyed and how new people still came to me.
Sooooo, you can only try and see what happens. Many congrats on the pregnancy and good luck! If you struggle, you can always advertise for adhoc care?