Background

Ultrasound has become an essential part of any early pregnancy assessment. This is particularly true during the first trimester when an ultrasound examination can confirm the number of fetuses, their viability, size and therefore gestational age. Ultrasound was primarily introduced to accurately date a pregnancy and thereby reduce perinatal mortality by decreasing the prevalence of postmaturity and identify multiple pregnancies. This is still relevant today but ultrasound now offers a great deal more information, which can be used to counsel patients and ensure they are appropriately managed throughout their pregnancy.

Classification of early pregnancy outcomes

One of the most important developments has been the identification of an ectopic pregnancy, an important cause of maternal morbidity and mortality and one that is often subject to substandard care. When an ultrasound examination is performed in early pregnancy there are three eventualities in terms of the location of the gestation sac: the pregnancy can be correctly located within the endometrial cavity (an intrauterine pregnancy), the pregnancy can be ectopically located (an ectopic pregnancy), or the pregnancy cannot be identified [a pregnancy of unknown location (PUL)].1 Intrauterine pregnancies may be viable, non-viable or of uncertain viability. The latter has been a subject of great debate in the media of late and national guidelines have recently been modified to extend the period during which non-viability can be confidently diagnosed to avoid inadvertent termination of a potentially viable pregnancy.2,–,4 These papers highlight the risks that may be associated with developing protocols in early pregnancy on the basis of insufficient data or ‘expert opinion’ alone.5

Ectopic pregnancies can exist outside of the uterus (a tubal or much less commonly an ovarian or abdominal pregnancy) or ectopically within the uterus (interstitial, cervical and Caesarean scar ectopics). Ultrasound can be used to positively identify the location of …