Human chorionic gonadotrophin (hCG) testing in medical abortion

A baseline quantitative serum hCG measurement is recommended before medical abortion. This should be repeated 7 days after the mifepristone is taken; a drop to below 20% of baseline confirms there is no continuing viable pregnancy. Measure the baseline quantitative serum hCG on the day (or as soon as possible before) the mifepristone is taken. The serum hCG concentration increases rapidly while the pregnancy is viable; the earlier the gestation, the faster the hCG will rise between baseline measurement and the mifepristone being taken. The fall in serum hCG concentration after medical abortion may require careful interpretation (particularly in early gestations) if the baseline was measured early.

Serum hCG measurement is also useful:

• for very early gestations (less than 5 to 6 weeks) to guide timing of the ultrasound scan for confirmation of intrauterine pregnancy
  • if the hCG is less than 1500 IU/L, an ultrasound should be delayed unless there is a suspicion of ectopic or nonviable pregnancy 
  • if the hCG is above 1500 IU/L, a high-quality transvaginal ultrasound will usually detect an intrauterine gestational sac; however, in the absence of a yolk sac or fetal pole this does not confirm an intrauterine pregnancy 
  • if the hCG is around 5400 IU/L, there is a 90% likelihood that a high-quality transvaginal ultrasound scan will detect a yolk sac, which confirms an intrauterine pregnancy 
• to assist with the diagnosis of nonviable and ectopic pregnancies in conjunction with serial ultrasounds.

If access to blood testing is difficult, a low-sensitivity urinary hCG test, taken at least 2 weeks after the dose of mifepristone, can be considered instead of baseline and follow-up quantitative serum hCG measurements. See Follow-up after medical abortion for more information.