The tankini is a great compromise between a one-piece and a bikini. They are becoming more and more popular for maternity wear and non-maternity wear.
Liz Lange says, "Go as bare as you dare. This is one time when you can afford to let it all hang out. String bikinis are cute. And if you're not feeling daring, a tankini is fantastic. It offers the sexiness of a bikini -- with coverage."