As the 5G standardization is underway, it has become apparent that the existing wireless fronthaul network needs to be redesigned in order to meet the future requirements. Passive optical network, with a shared fiber infrastructure, is an excellent candidate for 5G fronthaul transport. The 3GPP will complete the 5G New Radio standard in Release 15 by June 2018. The ITU-T Q2/SG15 group initiated the G.Sup.5GP project in June 2017 to study how 5G fronthaul requirements can be best supported by passive optical network. Many other standards development organizations have also been working on 5G transport standards, but their views are not yet fully aligned. The purpose of this paper is therefore not to provide a conclusion, but to report the recent progress in 5G related standards; to evaluate WDM and TDM based PON for 5G fronthaul, and to discuss the challenges ahead.