A pregnancy of unknown origin is diagnosed when a woman has a positive pregnancy test, but there are no signs of an intrauterine or extrauterine pregnancy on transvaginal ultrasound.

Causes

This can be due to three reasons:

• An early viable or failing intrauterine pregnancy
• A complete miscarriage
• An ectopic pregnancy

Investigations

• Serial serum B-hCGs 48 hours apart can help give an indication of the location and prognosis of the pregnancy.
  • If the levels fall (less then half the first reading) then it is suggested that the foetus will not develop or there has been a miscarriage
  • If there is only a slight increase or a plateau in B-hCG levels then this may indicate an ectopic pregnancy
  • A normal increase in B-hCG (double the first reading) suggests the foetus is growing normally, but does not exclude an ectopic pregnancy
• A transvaginal ultrasound may help to identify the location of the pregnancy, but in the early days of gestation the foetus may be too small to be accurately identified by ultrasound. In this instance it may be best to repeat the scan at a later date.