Early diagnosis of an ectopic pregnancy is important because it contributes to a decline in morbidity, maternal deaths and treatment costs. As the identification of an ectopic pregnancy can be difficult, the first step in ruling out ectopic pregnancy should be to identify intrauterine pregnancy which can virtually always be identi­fied after 5.5 weeks by transvaginal ultrasound. Quantitative hCG serum analysis is an important additional test, when an intrauterine pregnancy cannot be seen. Ectopic pregnancy should be assumed when the hCG serum test is above the dis­criminatory zone in which a pregnancy should always be detected by transvagi­nal sonography (TVS) (β-hCG concentrations =1500 IU/L).30 Sonographically, an extrauterine gestational sac surrounded by an echogenic ring consisting of the trophoblast at the implantation is usually seen (Fig. 4.18). Other ultrasound signs for ectopic pregnancy are any non-cystic extraovarian adnexal mass, complex cys­tic or solid masses and, of course, a living ectopic pregnancy, which is found in approximately 5–15% of cases. Viability of ectopic pregnancies can be evaluated by transvaginal Doppler ultrasound because of the good vascularization of the trophoblastic ring.

By simply looking at the image, it should be easy to distinguish whether the scan was done by TVS or TAS. Further, it must be possible to correlate TVS and TAS images from the same patient. When TVS and TAS images are standardized as indicated above, it is easy to recognize a TAS (‘pie apex up’) from a TVS (‘pie apex down’). In the transverse plane we will expect to find the patient's left ovary on the right side of the image and in the sagittal plane we will expect to find the bladder on the right side. If the uterus is pointing towards the right in a sagittal plane it is anteflexion; if it is pointing to the left, it is retroversion – no further explanation needed.

A screening obstetric ultrasound during the second trimester has been widely adopted around the world. This can provide important information regarding the pregnancy, including evaluation for placenta praevia, evaluation of the cer­vix and cervical incompetence and, most importantly, evaluation of the fetus. The fetus can be examined quite literally from head to toe, which has led to the concept of the fetal ‘anatomical survey’. Parents might even consider this their baby's first physical examination. In the vast majority of cases the fetus appears normal and parents can be reassured regarding the health of their baby. At the same time, a systematic fetal survey can now detect the majority of fetal mal­formations.1 A second-trimester scan is also desired by most prospective parents and has been found to be cost-effective, at least at centres that have reasonable accuracy for detection of fetal anomalies.

However, most centres now routinely include documentation of other