These cut-offs are accurate in a high percentage of patients with singleton pregnancies, but are subject to biologic as well single test error.
These outliers are not limited to multiple gestations.
Recent papers by Doubilet and Benson and Ko and Cheung have provided examples of women with titers greater than 2000 m IU/ml, where transvaginal ultrasound did not identify a early intrauterine sac, and a subsequent ultrasound confirmed a viable pregnancy.
The β-h CG cut-offs for visualizing a intrauterine pregnancy sac, a yolk sac, and a fetus with heartbeat are guidelines.
Alternatively for international readers, the website, isuog.org, of The International Society of Ultrasound in Obstetrics and Gynecology should be searched for similar guidelines.
Am J Obstet Gynecol 17, 1989) Fig 1A A very early, 3-mm mean diameter intrauterine gestational sac at 5 weeks postmenstruation Fig 1B A typical yolk sac.
The potential benefits of a subsequent ultrasound examination at 12–14 weeks from the LMP include: Similarly the standard of care for performing routine ultrasound at 12–14 weeks' gestation from the LMP varies from country to country.
The disadvantages are cost, decreased sensitivity for major anomalies compared to the 20 week exam, and marked increase in training requirements for providers.
The benefits of routine transvaginal ultrasound at 6–7 weeks from the LMP include: The standard of care for performing routine ultrasound examination at 6–7 weeks varies from country to country.
The disadvantages of performing this examination routinely are related to cost, errors in diagnosing ectopic pregnancies that in fact are intrauterine, increased training requirements for providers, and potential biologic hazards to the fetus that are presently unknown.