On occasion, it is preferable to freeze all embryos after retrieval rather than proceed with a fresh embryo transfer. The indications for doing this are several, and include both treatment effectiveness and patient safety.
From the patient safety perspective, if a woman is significantly hyper-stimstulated, or is at risk for increasing hyper-stimulation with a pregnancy , it is preferable to freeze all the fertilized embryo and schedule frozen embryo transfer at a later date. On occasion patients may also develop medical conditions such as cold or fever that may make the freeze-all a safer approach.
From the treatment effectiveness side, if the endometrial/uterine lining is thin on ultrasound, pregnancy rates are low with a transfer, and a better outcome can be obtained by transferring in a more controlled fashion in a frozen transfer cycle where sufficient estrogen is used to promote maximal uterine receptivity. A similar rationale is good justification for a freeze in the case of a trans-uterine puncture during retrieval, which can lead to cramping and bleeding and lower pregnancy rates with a fresh transfer. Increasingly we are also becoming aware that pregnancy rates during a fresh cycle transfer can be compromise on occasion through the stimulation medications used for the IVF, especially in the setting of high levels of Progesterone during stimulation. This also can be effectively treated with improved rates with a freeze-all and transfer in a separate cycle.
While delaying the transfer can be frustrating, this approach can lead to better outcomes with the right indications, and should be considered with an individualized approach based on the particular circumstances of the cycle.