Not familiar with Fort Leavenworth specifically, but if you already know that maternity care is not available on post they will put in a referral once you get there for a Dr out in town who accepts tricare prime. From there your coverage is 100% for anything "medically necessary" the same as it would be on post. You might get more u/s out in town, than on post, and they just code them as medically necessary and then they are covered. Your delivery is also covered 100% and any additional time your baby may need to spend in a NICU or something {hope you don't need this} is also covered 100% for anything "medically necessary."
We only have a naval health clinic on base here at Cherry Point {North Carolina} so I am seen out in town from the moment pregnancy is confirmed. I have a particular dr I see, but he accepts tricare prime and there are no issues. I also end up with a referral to the high risk dr's/hospital an hour away due to our issues, and everything with them is also fully covered.
Re: Fort Leavenworth