Why so nosey???

So I am 39 and 5 w4d my MIL watches our youngest while I work and the older 2 go to school. We have 3 girls and hubby just wants 1 boy. I told her yesterday that I have a dr appointment in September and she actually said “don’t tell me you are varying a little something” I told her I’ll know more after the appointment. She then goes on to lecture me about how I am 41 years old (remember I’m 39) and way to old to have more kids, What am I going to do when the world ends, and she’s not babysitting another one for me (for the record I never wanted her to babysit I only let her because hubby wanted it), and so on. Why does she have to be such a *****? Why is it her business and how dare she start asking before I’m ready to tell. She is so selfish and I’m so angry right now. I have started looking for someone else to watch our 3 year old, but it’s hard because we live in a rural area, but now I’m even more determined. I guess I just wanted to vent. Anyone else have to deal with a MIL like this?