The more your services are national in scope, the more a national banner ad becomes a practical option. When a user sees a banner ad on a Web page and clicks on that banner, then that action is considered a click-thru. In the last couple of years, the banner ad click-thru rates have fallen. You might want to consider an alternative to a banner ad, such as a page sponsorship. IHR offers banner ads and page sponsorships to infertility organizations.
Banners are useful for building brand because of the repetition factor.
You can place the banner on many targeted sites and people to gain attention. People see it once and it barely registers in their minds. People see it again and read it seriously for the first time. People see it one more time and pay attention. People see it yet again and recognize your logo and colors.