IVF and home pregnancy tests

I have a good friend who is going through <a href="https://glowing.com/glow-fertility-program">IVF</a>. She was advised not to do any home pregnancy tests. Well she took one Friday and it produced a positive test. She took another one today Sunday and it was negative. She's so confused now and I told her to just stay positive and wait for the blood test. I was just curious though what is the reasoning for not doing a home test? I am not familiar with the <a href="https://glowing.com/glow-fertility-program">IVF</a> process.