Advancing embryo transfer precision: narrative synthesis of four-dimensional versus two-dimensional ultrasound guidance in IVF

Infertility is becoming increasingly common and more people are turning to assisted reproductive technologies. However, success rates remain disappointingly low, and improving outcomes for every treatment is a major priority. Accurate embryo placement during embryo transfer (ET) is critical for implantation and livebirth. While two-dimensional (2D) ultrasound-guided embryo transfer (USGET) approaches are standard, evidence for four-dimensional (4D)USGET is limited. This review aimed to determine whether 4DUSGET improves embryo placement accuracy and clinical reproductive outcomes, informing clinical practice and guiding future research. A narrative review of literature across databases was performed. Data extraction included study design, sample size, embryo placement technique, and pregnancy outcomes. 4DUSGET was associated with enhanced accuracy of embryo deposition, particularly in women with abnormal uterine anatomy or when targeting the maximal implantation potential point. Several studies reported higher clinical pregnancy and livebirth with 4D compared to 2D guidance. Evidence base is limited by a small number of studies, heterogeneous outcomes and potential bias inherent to narrative syntheses, making definitive conclusions challenging. Nonetheless, emerging data suggest 4DUSGET may provide meaningful benefit in anatomically complex cases with the potential to improve IVF success rates. Trials are needed to confirm findings and establish generalisability across IVF populations.