How soon should we switch to tricare

My husband swears in on Wednesday so anytime after that my daughter and I can switch over to Tricare Reserve Select. I'm pregnant and was wondering what kind of copay and fees there are. I'm high risk so I see a specialist and my ob and high risk wants an ultrasound everytime to make sure the baby is growing correctly. Should I do it right away? Right jow we have state assistance but I don't know if or when we will loose that due to the fact that my husband is going National Guard and will only get paid for his weekends after training.