The invention provides novel heterodimeric fusion proteins comprising a first polypeptide including an alpha subunit of FSH (.alpha.FSH) linked directly or indirectly to a binding partner of neonatal Fc receptor (FcRn) and a second polypeptide including a beta subunit of FSH (.beta.FSH) linked directly or indirectly to an FcRn binding partner. In one embodiment the FcRn binding partner includes an Fc fragment of an immunoglobulin, e.g., an Fc fragment of IgG. Also provided are methods making and using the fusion proteins of the invention. The invention provides a method for increasing fertility in a subject and a method for treating a subject having a disease state responsive to treatment by FSH.