Afraid of maternity leave hurting career

We have been ttc for a long time with one loss in the mix. The more time goes on, the more I Wang a baby but also the more I worry about maternity leave. With being gone so long, my accounts will have to be passed along to others to handle. The person who will be covering most has been hungry to move up and to take some of my good accounts. I just get worried that they'll steal some of my accounts or that this will give them a leg up over me when it comes to promotion. I also feel like I'll be less valuable once I train others on everything i do and they prove they can handle it without me while im gone. Ive worked so hard to gey where i am and hope to keep moving up but also want a family! Help! How do I not stress about this when I have so much else to worry about it as it is?