jules - an opk is an ovulation prediction kit. it's a home test to track ovulation. dependin on the type of FET, the clinic may ask you to use the OPK to track for ovulation at home, or you may be asked to come in for BT's - this is assuming you ovulate! when ovulation is detected, you'll be asked to come in however many days after ovulation your embies have developed to. so, for a blast - it's likely to be day five or six after ovulation

if, like me, you don't ovulate, or your clinic prefers a medicated FET, you may have to use HRT meds until a day they predetermine as ovulation day (minus the ovulation) - then they'll start you on progesterone to create an artificial luteal phase. again, your embie will be transferred on the number of days post O that it was frozen

hope that helps hun

BG