Introduction
Being one of the key parameters of endometrial receptivity, endometrial
thickness plays an important role in successful embryo implantation (1)
.Although there has been no commonly accepted thickness below which
successful implantation would be preclude, it has been recognized by
many investigators that endometrial thickness ≥7mm on the day of
luteinizing hormone(LH)
surge or human chorionic gonadotrophin(HCG) administration is preferred
for embryo transfer(2-5). Thin endometrium (<7 mm) affects about 2.4%
patients in in vitro fertilization(IVF) cycles (6).It often results in
cancelation of embryo transfer and cryopreservation of all the embryos.
Various strategies have been attempted to improve endometrial growth in
these patients, including estrogen supplementation, vasoactive measures
such as vaginal sildenafil, low-dose aspirin, pentoxifylline, or
tocopherol, intrauterine infusion of granulocyte colony‑stimulating
factor, and regenerative medicine(7-11). Among them, exogenous
estrogen treatment is the most commonly used method(12). Many factors
may influence the effectiveness of estrogen treatment and the subsequent
reproductive outcomes(12-14).Although high dose estrogen treatment
sustaining a long time may be effective for some of these
patients(12), supraphysiologic estrogen levels resulted from this
treatment may have a negative impact on reproductive outcomes(15-19).
Moreover, a higher risk of side-effects, such as breakthrough bleeding
(20), some types of tumor such as endometrial cancer (21), deep venous
thrombosis (22) may also be associated with this treatment. Furthermore,
after pregnancy, exogenous estrogen and progesterone should be continued
until 8-10 weeks of
gestation
to substitute for the absent corpus luteum. In addition, some patients
were insensitive to estrogen treatment. Alternative methods should be
considered for endometrium preparation in these women during their
frozen embryo transfer (FET) cycles.
Tamoxifen (TAM) is a selective estrogen receptor modulator (SERM) with
chemical properties similar to clomiphene citrate (CC).It has been used
in clinic as a highly effective agent for the treatment of breast
cancer(23)and anovulation(24-26). In contrast to CC, whose
anti-estrogenic effects at the level of the endometrium sometimes result
in thin endometrium(27), ovulation induction with tamoxifen improves
endometrial thickness in women with a history of thin endometrium (28).
However, little information is available regarding its use during FET
cycles in that kind of patients. To
the best of our knowledge, there has been three published study
investigating the use of TAM for endometrium preparation (EP) in thin
endometrium patients. The first one is only a case report (29).The
obvious weakness of the other two studies is that there were no control
groups (30, 31). Furthermore, they are limited by their small sample
size. The aim of this study is to evaluate the efficacy of TAM in women
with thin endometrium during their FET cycles through comparing it with
the most commonly used protocol- hormone replacement treatment (HRT)
protocol. We propose that the result of our study may contribute to the
treatment of infertility patients with thin endometrium.