Ultrasound scan before medical abortion

A transabdominal or transvaginal ultrasound scan is routinely recommended before medical abortion to determine gestation and viability, and to confirm that the pregnancy is intrauterine. Although extremely rare, simultaneous ectopic and intrauterine (heterotopic) pregnancies can occur; an ectopic pregnancy is not excluded by confirmation of an intrauterine pregnancy.

Diagnosis of an intrauterine pregnancy on transabdominal or transvaginal ultrasound is usually not possible before 5 weeks’ gestation because it requires visualisation of specific structures within the intrauterine gestational sac (either a yolk sac or a fetal pole). If an intrauterine sac without a yolk sac or fetal pole (an empty gestational sac) is seen on a transabdominal ultrasound, a transvaginal ultrasound is necessary. Causes of this ‘empty gestational sac’ include:

  • very early intrauterine pregnancy (yolk sac and fetal pole are rarely seen before 5 weeks’ gestation); see also Very early medical abortion
  • ectopic pregnancy, which can cause a collection of fluid in the uterus (pseudosac)
  • nonviable pregnancy.
Note: Early gestation is the most common reason that an ultrasound shows either an empty uterus or a gestational sac without a yolk sac or fetal pole, but always consider ectopic or nonviable pregnancy.

If intrauterine pregnancy could not be confirmed by the initial transvaginal ultrasound scan, but the date of the last menstrual period and the serum hCG concentration are consistent with a very early pregnancy, repeat the ultrasound after 1 to 2 weeks. A further serum hCG test may be useful in conjunction with ultrasound to confirm viability or exclude ectopic pregnancy.

If the date of the last menstrual period, serum hCG concentration and ultrasound findings give discrepant estimations of gestation, the risk of a nonviable or ectopic pregnancy is increased. Next steps include:

  • informing the individual of the symptoms of ectopic pregnancy
  • performing serial transvaginal ultrasound scans and serum quantitative hCG measurements, and monitoring until a diagnosis is established or until specialist review
  • considering referral to or consultation with an early pregnancy assessment unit.

If intrauterine pregnancy cannot be confirmed on a transvaginal ultrasound scan, very early medical abortion (VEMA) may be considered by highly experienced providers, bearing in mind that the pregnancy could be ectopic or nonviable. If VEMA is not being performed, management depends on menstrual history and the serum hCG concentration.