First trimester ultrasound.

First-trimester ultrasound, performed between 11 and 14 weeks' gestation, has become a cornerstone of modern prenatal care, supporting early risk assessment and guiding subsequent pregnancy management. This review summarises current principles, clinical applications, and practical considerations in first-trimester ultrasound, including confirmation of viability, accurate pregnancy dating, determination of chorionicity in multiple pregnancies, and early anatomical assessment. The scan also enables screening for chromosomal abnormalities through measurement of nuchal translucency and evaluation of additional sonographic markers, while complementing non-invasive prenatal screening by providing essential structural information. Systematic assessment further allows early detection of major fetal anomalies, evaluation of placental location and placenta accreta spectrum risk, screening for pre-eclampsia, and identification of uterine or adnexal pathology. Emphasis is placed on standardised protocols, operator training, appropriate equipment, and optimisation of imaging techniques to maximise diagnostic accuracy. As technology and expertise continue to advance, first-trimester ultrasound plays an increasingly central role in improving maternal and fetal outcomes through early, integrated prenatal evaluation.