Investigations in Early Pregnancy: Ultrasound

Transvaginal ultrasound (US) is the diagnostic modality of choice for ectopic pregnancy. [28]

At around 5 weeks gestational age, a normal intrauterine gestation sac can be visualized.

Visualisation of a gestational sac does not confirm intra-uterine pregnancy as the hormonal environment of an ectopic pregnancy can produce an intrauterine fluid collection that mimics a gestational sac.

Ultrasound image

Fig. 1 Image reproduced under creative commons licence from Wikimedia/Dr James Heilman.

In this image, note the yoke sac and double ring sign (arrowed) as seen in early pregnancyapprox 5 weeks.

An awareness of the limitations of US is as follows:

• Cardioactivity needs to be seen to confirm intra-uterine pregnancy
• Cardioactivity can be seen at gestational age 6-6.5 weeks
• Cardioactivity does not exclude ectopic pregnancy in patients undergoing fertility treatment who are at risk of a heterotopic pregnancy. [14]
• Absence of an intrauterine pregnancy translates to a risk of ectopic of about 36%. [15]

Heterotopic pregnancy

This demonstrates a heterotropic pregnancy. An intrauterine growth sac is present together with an ectopic pregnancy in the fallopian tube in the same patient.

Important: Beware of heterotopic pregnancy in patients undergoing fertility treatment.