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.
In this image, note the yoke sac and double ring sign (arrowed) as seen in early pregnancyapprox 5 weeks.
Image reproduced under creative commons licence from Wikimedia/Dr James Heilman.
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].
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.