Modern IVF achieves higher success rates with single embryo transfer, major study finds

Modern IVF treatment can now achieve substantially higher success rates than historical approaches while dramatically reducing twin and triplet pregnancies, according to new research presented today at the 42nd Annual Meeting of the European Society of Human Reproduction and Embryology (ESHRE).

In one of the largest IVF studies of its kind, researchers analysed outcomes from 18,396 women undergoing their first IVF cycle between January 2012 and December 2021 across seven Australian fertility clinics, with follow-up through December 2023.

The research found that modern IVF clinical practices achieved a 68.2% cumulative live birth rate over three treatment cycles, while using single embryo transfer in 95.3% of embryo transfers and maintaining a multiple birth rate of just 2.9%.

The findings mark a notable improvement on historical IVF outcomes. Earlier studies, conducted before the widespread adoption of modern IVF laboratory techniques, reported three-cycle cumulative live birth rates of around 53–59%, often alongside multiple pregnancy rates exceeding 20%. The researchers say the improved outcomes likely reflect advances including blastocyst culture, embryo vitrification, freeze-all strategies and optimised frozen embryo transfer protocols, now widely used in contemporary IVF care.

Researchers examined cumulative live birth rates across up to three IVF cycles using contemporary clinical protocols, including extended blastocyst culture (day 5–6 embryo development), embryo vitrification (rapid freezing) and elective freeze-all approaches where appropriate. Women using donor eggs, frozen eggs or specific genetic testing pathways were excluded from the analysis. Across all women, the cumulative live birth rate over three treatment cycles reached 58.7% using intention-to-treat analysis and 68.2% using optimal per-protocol analysis.

Success rates varied substantially by age. Women under 35 achieved an optimal cumulative live birth rate of 84.5%, compared with 74.4% for women aged 35–37, 57.7% for women aged 38–40 and 30.1% for women aged 41–42.

Lead author Dr Dean Morbeck said the findings reflect a decade of incremental advances in IVF laboratory and clinical practice.

“The biggest shift has been that blastocyst culture has moved from being an exception to becoming the default,” Dr Morbeck explained. “That change drove improvements across IVF laboratories, including reduced oxygen conditions, purpose-built incubators and minimised disruption to embryos during culture.”

“Blastocyst culture also became much more effective with vitrification, which dramatically improved embryo survival after freezing and warming, making frozen embryo transfer outcomes comparable to fresh transfers. Together, these advances enabled approaches such as freeze-all treatment, where embryos are transferred one at a time later, rather than during the initial stimulation cycle.”

The study also examined changes over time, comparing outcomes before and after laboratory improvements introduced from 2016 onwards, including single-step culture medium and time-lapse embryo culture. Between 2012–2015 and 2017–2021, the proportion of fertilised eggs developing into usable blastocysts increased from 48.3% to 57.6%, while single embryo transfer increased from 92.8% to 97.3%. Over the same period, the multiple birth rate fell from 3.2% to 2.7%.

Dr Morbeck said the findings challenge the longstanding assumption that transferring multiple embryos is necessary to maximise IVF success.

“For many years, transferring two embryos increased the chance of pregnancy from any one transfer, but often came with twin pregnancy rates approaching 30%,” he explained. “What our data show is that this trade-off has largely disappeared.”

“Across more than 18,000 women, we achieved strong cumulative live birth rates while using single embryo transfer in 95% of cases and maintaining a twin birth rate under 3%. A concerted effort to reduce twin pregnancies has not cost patients their chance of taking home a baby – it has coincided with that chance increasing.”

The findings also suggest that strong IVF outcomes can be achieved without routine use of preimplantation genetic testing for aneuploidy (PGT-A) – a test used to screen embryos for chromosomal abnormalities before transfer – in all patients.

PGT-A was used in one or more treatment cycles in 25% of women included in the study. However, Dr Morbeck noted that most live births occurred without routine embryo genetic testing.

“PGT-A has an important role for some patients, particularly women of advanced maternal age and those with recurrent pregnancy loss,” he said. “But our findings should reassure many patients that strong IVF outcomes are achievable without routine genetic testing necessarily being required.”

Discussing the implications of the findings, Dr Morbeck said the results support continued efforts to increase access to single embryo transfer internationally. “The future of IVF is continuing to improve the success rate of each embryo transfer while maintaining the safety gains we’ve achieved,” he said.

Reflecting on the significance of the research, Professor Borut Kovacic, Chair-elect of ESHRE, said: “Improvements in IVF are typically driven by steady, incremental advances rather than dramatic breakthroughs. This study demonstrates that optimising laboratory practices, adhering to evidence-based guidelines and adopting a relatively conservative treatment approach can progressively increase cumulative live birth rates while reducing multiple births – two outcomes that matter most to patients seeking a safe and cost-effective route to parenthood within a single stimulation cycle.”

Reference:

Modern IVF achieves higher success rates with single embryo transfer, major study finds, European Society of Human Reproduction and Embryology, Meeting: ESHRE 42nd Annual Meeting