More and more frequently doctors recommend their IVF patients freeze all of their embryos before making a transfer. To the positive, the approach makes it easier to genetically-test the embryos, reduces rates of OHSS, and theoretically gives the endometrium time to recover and clinicians the chance to find the window when it's most receptive to receive the embryo.
On the other hand, freeze-only approaches are likely only as productive as the (wide variety of) laboratories handling the embryos, have been associated with "large for gestational age" offspring and likely add to the patient's total bill for that cycle.
Why This Study Was Special
Studies analyzing the value of freeze-only cycles have been extremely small in nature and performed at the hands of one or two clinicians at a single center. We just can’t say if their findings (which are supportive of freeze-only) apply to a broad group of fertility patients who will be treated at a spectrum of clinics (with varying degrees of laboratory freeze / thaw skill).
This study addresses a number of these shortcomings. It involves a large number of cycles (nearly 1,500 cycles, 3 - 10x more than we're accustomed to), performed on a broad variety of patients, treated at over 12 clinics and nicely matches the freeze-only group to a control group of patients that appear similar and who had a fresh embryo transfer.
What Was Tracked And What They Found
The investigators looked at Ongoing Pregnancy Rates (but not Live Birth Rates, a shortcoming) and found that patients who had freeze-only cycles outperformed their matched cohorts. However, the difference was only meaningful when the woman had a Progesterone level >1.0 ng/mL. At that level, or below, there was no statistical difference. It appears that within each Progesterone range, women ages 36 and above saw more benefit than women 35 and younger.
The Study’s Limitations
First, the study did not include an assessment of Live Birth Rate. Patients care about taking home a baby and so anything short of measuring this is probably incomplete. We’ve seen plenty of studies where therapies improve pregnancy rates but don’t improve actual take-home baby rates.
Second, the trial was not prospectively randomized and so we cannot be certain the groups being compared are in fact similar, or if the treatment is responsible for any difference in outcome we saw above.
Third, these patients were able to make multiple blastocysts and so what was seen may not apply to poor responders.
Freeze-only is not equally helpful for all fertility patients. It's worth having a refined, data-driven discussion with your doctor about the benefits freeze-only confers and where (and for whom) it's yet to drive higher live birth rates.
You can see a more complete description of the data on fresh vs. frozen embryos here.