Infertility, defined as the inability to achieve a clinical pregnancy after 12 months of unprotected intercourse, is a global concern, affecting approximately 10% of couples worldwide. The causes of infertility are diverse, with women contributing to 20-35% of cases, men to 20-30%, and both partners involved in 25-40% of cases. Assisted Reproductive Technologies (ART), such as in-vitro fertilization (IVF) and intracytoplasmic sperm injection (ICSI), have become pivotal in addressing these challenges. While IVF remains a cornerstone for treating female infertility, ICSI has emerged as a highly effective treatment for male infertility, boasting success rates of up to 70%.
A critical step in ART procedures is embryo transfer (ET), which can be conducted as either a fresh or frozen transfer. In fresh ET, embryos are transferred typically within 3-5 days after retrieval, while in frozen ET, previously frozen embryos are thawed and implanted after an endometrial preparation cycle. Both methods require careful endometrial preparation to optimize embryo implantation. Recent studies have shown that frozen ET may increase live birth rates in certain patient populations, such as hyper-responders or those undergoing preimplantation genetic testing. Additionally, frozen ET may reduce the risk of severe ovarian hyperstimulation syndrome (OHSS), although it could slightly elevate the risk of preeclampsia.
Despite its advantages, the debate surrounding the efficacy of frozen versus fresh ET persists. Some research suggests that frozen ET improves IVF outcomes compared to fresh transfers, while others report no significant differences in pregnancy and live birth rates. Frozen embryos are particularly beneficial in cases where fresh embryo transfer fails or when there are medical contraindications, such as OHSS. One major benefit of using frozen embryos is the ability to prevent multiple pregnancies by transferring fewer embryos at a time, which is crucial in reducing the risks associated with miscarriage and premature birth.
The rise in the use of frozen ET is also attributed to its flexibility—embryos can be stored for future use, and transfer timing can be synchronized with the woman’s natural cycle or a hormone-prepared cycle. Furthermore, freezing embryos allows for genetic testing and the selection of the best embryos, which has become an important aspect of modern ART procedures.
However, the existing literature provides conflicting evidence regarding the optimal approach. For instance, a study revealed that while both frozen and fresh blastocyst transfers resulted in similar growth trajectories, the frozen group showed higher fetal weight and birth-weight Z-scores. Another study indicated that thawed blastocysts resulted in a greater crown-rump length at 6-14 weeks of gestation compared to fresh embryos, though both IVF/ICSI groups exhibited smaller measurements than the general population. These discrepancies highlight the need for further investigation into the long-term effects of frozen versus fresh embryo transfers on pregnancy and neonatal outcomes.
Given the complexity and high emotional and financial costs associated with ART, it is essential that infertile couples are fully informed before embarking on these treatments. Understanding the potential benefits and limitations of fresh and frozen embryo transfers is crucial for making informed clinical decisions. Moreover, the variability in ART protocols across different centers contributes to inconsistent results, emphasizing the need for more rigorous, comparative studies.
At Al-Zahra Hospital in northwestern Iran, a prominent referral center for ART in the region, the outcomes of fresh and frozen embryo transfers have not been extensively studied. This gap in knowledge is particularly relevant for low-income couples who may have limited access to ART services. This study aims to provide critical insights into the pregnancy, prenatal, and postnatal outcomes of both transfer methods in ICSI cycles at this hospital, contributing to more effective clinical decision-making and improved fertility treatment options.
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