Endometrial preparation protocols
In this study, different methods of endometrial preparation methods were
non-selectively and consecutively recorded, and used exposure variables
to observe the correlation with live birth rate and other clinical
outcomes. The type of endometrial preparation was determined by the
treating physician’s preference, based on patients’ characteristics. In
general, women with regular ovulation were allocated to natural cycles
(n=1676), while patients who were reluctant to frequently monitoring or
living far from the hospital were allocated to artificial cycles
(n=8057). The detailed protocols for NC and AC endometrial preparation
were described as follows:
1) Natural cycles for FET
Follicle monitoring began on day 8-10 of the menstrual cycle. When the
leading follicle reached a mean diameter of >17mm, serum
luteinizing hormone (LH) was <20 IU/L, 10000 IU of human
chorionic gonadotropin (hCG) was administered to trigger oocytes
ovulation. Ovulation was confirmed by transvaginal ultrasound the day
after hCG and the next day. When LH was >20 IU/L,
transvaginal ultrasound was performed every day until ovulation.
Artificial cycles for FET
In women treated with AC,
endometrial priming started on the fifth day of the menstrual cycle with
estradiol valerate (Progynova; Bayer Schering Pharma AG, Berlin,
Germany) orally administered at a dose of 6mg daily. After 10-12 days of
endometrial preparation, transvaginal ultrasound and progesterone level
were performed. In women with endometrial thickness >8mm
and serum progesterone (P) level <1.5ng/ml, intramuscular
progesterone at a dose of 60mg daily was administrated.
The timing of FET was based on the
day of embryo freezing and the day of ovulation (i.e., 3 days after
ovulation for cleavage stage embryos and 5 days after ovulation for
blastocyst stage embryos). Triple-line endometrial pattern of
endometrium was classified as pattern A (a triple-line pattern
consisting of a central hyperechoic line surrounded by two hypoechoic
layers), pattern B (an intermediate isoechogenic pattern with the same
reflectivity as the surrounding myometrium and a poorly defined central
echogenic line), and pattern C (homogenous, hyperechogenic endometrium)8.