New Use for Letrozole before Embryo Transfer
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This study adds letrozole to hormonal therapy before frozen embryo transfer (FET).
Study Background
WHAT
Does adding letrozole for five days onto estrogen-progesterone protocols for FET improve rates of pregnancy?
WHY
Increasing studies show that letrozole can benefit embryo implantation
Lack of research adding letrozole to hormone treatment shortly before embryo implantation = interest in impact on ongoing rate of pregnancy
WHERE
Obstetrics and Gynecology Department, Zagazig University, Cairo, Egypt
WHEN
August 2020- February 2021
WHO
Women ages 18-37
One good-quality blastocyst (day 5) available for transfer
Endometrial lining at least 9 mm after supplemental estrogen
HOW
Oral estradiol valerate (2 mg three times daily) started on Day 2 or 3 targeting endometrial thickness of 9 mm or greater
Once desired thickness reached, randomization by sealed envelope method* in 1:1 ratio into two groups
Letrozole Group = added on five days of oral letrozole (2.5 mg twice daily) to oral estrogen before starting intramuscular progesterone in oil (100 mg daily)
Control Group = oral estrogen, no letrozole, then addition of intramuscular progesterone
*Uninvolved assistant determined randomization, patient selected envelope
Frozen embryos warmed and transferred on progesterone day 6
Post-embryo transfer, added daily progesterone (100 mg intramuscular once daily + oral 100 mg three times daily) and continued estradiol
If clinically pregnant, started vaginal progesterone at 100 mg three times daily, continued oral estrogen and progesterone, and decreased intramuscular progesterone to every third day.
Stopped supplemental estrogen and progesterone at 10 and 12 weeks gestation, respectively
Ongoing pregnancy: fetal cardiac pulsation at 12+ weeks gestation
Statistics (for the Uber Curious)
Sample size N= 56 women per group calculated from:
Needed 54 women per group for Chi-square test for independent samples; alpha error 0.05, power of 80%
Pilot study of 25 women showing ongoing pregnancy of 80% (letrozole) vs. 55% (control)
expected cancellation of embryo transfer of 4%
Results
55 women analyzed in Letrozole Group; 54 women analyzed in Control Group
Ongoing pregnancy rates higher in Letrozole Group vs. Control Group (RR 1.39, 95% CI 1.04-1.86, p =0.023)
Clinical pregnancy rates higher in Letrozole Group vs. Control Group (RR 1.31, 95% CI 1.02-1.68, p =0.03)
No statistical significance between groups for endometrial compaction (p =. 0.776)
Estradiol levels in N = 40 of Letrozole Group:
26.6% decline from reaching target endometrial thickness on estrogen and finishing letrozole (p < 0.001)
12.6% increase on day of FET (p =0.015)
16% median decline from reaching target endometrial thickness to day of FET ( (p < 0.001)
Authors’ Thoughts
Study limitations: no placebo, no data on live births, results limited to inclusion criteria
Letrozole: used here to decrease estradiol and increase implantation
Drug may accrue within endometrium, lasting beyond half-life of ~48hr; mechanism of action is presently unknown
First known study of this drug used, not with gonadotropins, but after / during estrogen prep and before starting progesterone
Supplementary estradiol and progesterone (HRT) based on prior research + unit protocol
Endometrium
Necessary to have adequate estradiol priming to proliferate endometrium and induce progesterone receptors - selected target of 9 mm endometrial thickness to maximize outcomes
Ongoing and clinical pregnancy not affected by state of endometrial compaction (and compaction not impacted by estradiol)
This Pharmacist’s Thoughts
(+) carefully researched prior to manuscript publication, adequately powered, letrozole is cheap and convenient to take (feasible add-on for most women doing embryo transfer)
(-) unblinded, study did not disclose all methodology involving sealed envelope randomization - were additional security measures used?
Conclusions
This study offers an exciting first look at a new role for letrozole in helping women to conceive. Clearly, more studies are needed that are blinded, record live birth rates, and test alternate dosing regimens of estradiol and progesterone.
Resources
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