Abstract
Research questionEndometrial preparation is one of the most important steps for ensuring frozen embryo transfer success. However, there is no clear evidence that identifies an optimal endometrial preparation protocol for frozen embryo transfer. In addition, in studies that assessed which were the optimal endometrial preparation protocols, few analyzed the stage and the number of embryos. This study compared the pregnancy outcomes and perinatal obstetric complications of patients who were transferred two cleavage-stage (day 2 or day 3) frozen embryos with the natural cycle and those with the hormone replacement therapy cycle.DesignThis study was a secondary analysis of data from a multicentre randomized controlled trial designed to compare the pregnancy and perinatal outcomes after frozen versus fresh embryo transfer. In this study, a total of 908 patients who were transferred two cleavage-stage (day 2 or day 3) embryos in the original trial were analyzed. Pregnancy outcomes and perinatal obstetric complications after the natural cycle and the hormone replacement therapy cycle were compared.ResultWe found the endometrium in the natural group was significantly thicker than the hormone replacement therapy cycle group (p<0.01). The implantation rate (42.6% vs 37.3% p=0.049) showed a significant difference between the natural cycle group and the hormone replacement therapy cycle group. Compared to the natural cycle group, the hormone replacement therapy cycle group was associated with an increased risk of caesarean section (72.3% vs 84.5, p=0.009).ConclusionThe natural cycle protocol yielded thicker endometria, a higher implantation rate and a lower risk of caesarean section than the hormone replacement therapy protocol in the transfer of two cleavage-stage frozen embryos. The natural cycle protocol was the better endometrial preparation protocol for frozen embryo transfer.
Highlights
In 1983, the first successful pregnant of frozen embryo transfer (FET) was reported in humans, and FET technology has been widely applied in the clinic ever since [1]
Patients in the natural cycle group underwent a longer duration of infertility and lower body mass index (BMI) than patients in the hormone replacement therapy (HRT) cycle group
The endometrium in the natural group was significantly thicker than it was in the HRT cycle group (p
Summary
In 1983, the first successful pregnant of frozen embryo transfer (FET) was reported in humans, and FET technology has been widely applied in the clinic ever since [1]. The development of cryopreservation technology has made the frozen-thawed embryo process safer. Because of avoiding the influence of supra-physiologic hormonal levels in controlled ovarian stimulation, which enables the process of assisted reproductive technology to be safer and improves pregnancy outcome, FET (even the freeze-all strategy) has been used with increasing frequency [7, 8]. Some reports indicated that the protocols of endometrial preparation may be relevant for pregnancy and obstetric outcomes after FET [11, 12]. Identifying whether the protocols used for endometrial preparation influence the outcomes of FET is a primary research interest at the present time
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