Well, I don’t think NYC phrased what she said very well. It’s more that anti-malaria drugs often aren’t suitable for someone who is pregnant. Depends on which drug is used.
However, malaria can cause pregnancy complications.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3687872/

So, I can understand avoiding attempts for Megs to get pregnant in Africa. She’s of advanced maternal age at this point, which leads to complications already. That’s even assuming she is able to get pregnant.