Where did you get this info from? When Michelle was pregnant with her youngest daughter they showed her going to the doctor's office, and then they interviewed her doctor. Her doctor said that Michelle is very healthy and there is no problem with her many pregnancies. She's had the same doctor for at least her last several pregnancies, so the rumors that were going around earlier this year that her doctors keep dropping her because she keeps getting pregnant were/are not true.
For the record, I like this family very much and enjoy their show and the way they're raising their children, but I definitely would not choose to have so many children, and I was surprised at the recent announcement of another pregnancy.