B1/B2 visa holder

cannot work here including takeing care of you and your baby. That's against law and maybe the reason why they turned your parents down. If you and your baby need to be taken care, go ahead to hire somebody else here. That's the job opportunity for somebody. I don't think the company's letter will help your case a lot. Normally, your or your hu*****and's invitation is enough. Try again and provide evidence for strong tie in China such as your parent might have some kind of job in China and earn a lot of money from that job. And they come here just for travelling. However, if they are asked about your pregnacy, don't lie.