Criteria

Overview of the most common pregnancy loss events and ultrasound findings[85]

Biochemical pregnancy loss:

  • Typical gestation <6 weeks

  • No fetal activity ever detected

  • Pregnancy not located on ultrasound

  • Beta hCG levels are low and then fall.

Early pregnancy loss:

  • Gestation typically 6 to 8 weeks

  • No fetal activity ever detected

  • Empty sac or large sac with minimal structures without fetal heart activity

  • Beta hCG levels show an initial rise and then fall.

Late pregnancy loss:

  • Typical gestation >12 weeks

  • Loss of fetal heart activity

  • Crown to rump length and fetal heart activity previously identified.

Ultrasound diagnostic criteria for nonviable miscarriage[69]

Complete miscarriage:

  • No intrauterine gestational sac and no ovarian or fallopian mass

  • No evidence of early pregnancy tissue in uterus

  • A heterogeneous shadow within the uterine cavity <15 mm in longitudinal section.

Note that, in women with ultrasound features suggesting complete miscarriage, if there are no previous ultrasound scans documenting the presence of an intrauterine pregnancy, they should be managed as having a pregnancy of unknown location and they will be required to have serum hCG levels to check resolution of the pregnancy.[68]

Incomplete miscarriage:

  • No intrauterine gestational sac and no ovarian or fallopian mass

  • Heterogenous shadows within the endometrial cavity of mixed echogenicity with or without blood flow/doppler signals is suggestive of retained products of conception.

Missed miscarriage:

  • Empty intrauterine gestational sac measuring ≥25 mm or no increase in gestational sac size on two ultrasound scans performed between 7 and 10 days apart (transvaginal ultrasound scanning [TVUS])

  • Crown to rump length is ≥7 mm with no fetal heartbeat.

Although the diagnostic criteria are specific, they are not always conclusive in situations such as a pre-event finding of a fetal heart rate <120 beats per minute.[86]

The diagnosis of miscarriage based on one ultrasound scan cannot be guaranteed as accurate, particularly if it is a very early gestation age. The UK National Institute for Health and Care Excellence offers this guidance regarding the follow-up of an ultrasound scan:[68]

  • If the crown-rump length is <7 mm with a TVUS and there is no visible heartbeat, perform a second scan a minimum of 7 days after the first scan before making a diagnosis. Further scans may be needed before a diagnosis can be confirmed

  • If the crown-rump length is ≥7 mm with a TVUS and there is no visible heartbeat, seek a second opinion on the viability of the pregnancy and/or perform a second scan a minimum of 7 days after the first scan before making a diagnosis

  • If the mean gestational sac diameter is <25 mm with a TVUS and there is no visible fetal pole, perform a second scan a minimum of 7 days after the first scan before making a diagnosis. Further scans may be needed before a diagnosis can be made.

  • If the mean gestational sac diameter is ≥25 mm using a TVUS and there is no visible fetal pole, seek a second opinion on the viability of the pregnancy and/or perform a second scan a minimum of 7 days after the first scan before making a diagnosis.

  • If a transabdominal ultrasound scan is used (e.g., for women with an enlarged uterus or another pelvic pathology), then a second scan should be repeated a minimum of 14 days after the first scan.

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