On the day of ET, patients will be randomized according to a computer-generated randomization list in sealed envelopes into two groups: conventional and protective ET catheter groups. Conventional ET catheters will be used in the conventional ET catheter group while protective ET catheters will be used in the protective ET catheter group. Patients would be blinded to the group assigned although the clinical, nursing and laboratory staff will be aware of the type of catheters used.