Diagnosing twins in early pregnancy.

Multiple pregnancy has increased in frequency as a result of the ageing maternal population as well as the advent and wider availability of assisted reproductive technologies. Higher-order pregnancies are associated with increased morbidity and mortality for both the foetuses and mother. The introduction of transvaginal ultrasound has made accurate diagnosis of twin pregnancy, determination of chorionicity and subsequent planning of these high-risk pregnancies a common part of obstetric care. In this article, we critically evaluate the role of transvaginal ultrasound in the diagnosis of twin pregnancies.