Embryo Transfer Outcomes in Assisted Reproductive Technology
Summary
Embryo transfer remains a pivotal step in assisted reproductive technology, directly influencing obstetric and perinatal outcomes. Both fresh and frozen–thawed embryo transfers have been deployed to optimise implantation rates and live births, yet their downstream effects on maternal health and infant development differ. Fresh transfers occur in hormonally stimulated cycles and may be subject to supraphysiological hormone levels, while frozen transfers allow endometrial recovery in a more natural hormonal milieu. Recent advances in vitrification, culture media and embryo selection have improved survival rates and expanded the use of frozen–thawed transfers. Clinical concerns now centre on relative risks of hypertensive disorders, abnormal foetal growth trajectories—small for gestational age versus large for gestational age—and preterm delivery. Meta-analyses and population studies have begun to disentangle the contributions of treatment protocols from parental factors, highlighting the need for tailored cycle planning. Globally, understanding these differences informs guidelines on cycle scheduling, luteal support and patient counselling, with the aim of optimising both safety and efficacy in varied healthcare settings.
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Embryo Transfer Outcomes in Assisted Reproductive Technology publication trend
The graph below shows the total number of articles in embryo transfer outcomes in assisted reproductive technology across all publications each year (not limited to Nature Index journals).
Technical terms
Fresh embryo transfer: Transfer of embryos in the same ovarian stimulation cycle without prior cryopreservation.
Frozen–thawed embryo transfer (FET): Transfer of embryos after cryopreservation and subsequent warming, often in a separate menstrual cycle.
Programmed cycle: An endometrial preparation protocol using exogenous oestrogen and progesterone to synchronise the uterine lining.
Blastocyst: An embryo typically five to six days post-fertilisation, with differentiated inner cell mass and trophectoderm.
Small for gestational age (SGA): Birthweight below the 10th percentile for gestational age.
Large for gestational age (LGA): Birthweight above the 90th percentile for gestational age.
Hypertensive disorders of pregnancy: A spectrum including gestational hypertension and pre-eclampsia arising after 20 weeks’ gestation.
References
- The influence of embryo stage on obstetric complications and perinatal outcomes following programmed compared to natural frozen-thawed embryo transfer cycles: a systematic review and meta-analysis. Frontiers in Endocrinology (2023).
- Fetal growth after fresh and frozen embryo transfer and natural conception: A population‐based register study. BJOG An International Journal of Obstetrics & Gynaecology (2024).
- Separating parental and treatment contributions to perinatal health after fresh and frozen embryo transfer in assisted reproduction: A cohort study with within-sibship analysis. PLOS Medicine (2021).
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