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1st trimester ultrasound dating

The β-h CG cut-offs for visualizing a intrauterine pregnancy sac, a yolk sac, and a fetus with heartbeat are guidelines.These cut-offs are accurate in a high percentage of patients with singleton pregnancies, but are subject to biologic as well single test error.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.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.Today's obstetrician gynecologist is required to interpret and in many cases perform ultrasound scans in the first trimester.In fact, certification of residency programs in many countries requires documentation of adequate exposure to and training in the evaluation of first-trimester ultrasound.Any health-care provider performing diagnostic ultrasound must understand the physics of diagnostic ultrasound and have thorough, supervised training.

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.

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 mean sac diameter of the gestational sac is 10.6 mm.

If your suspected date of conception is further off than that, they will just think your dates are wrong and use the ultrasound date. I had an early scan with this pregnancy and going by my LMP I was 8weeks exactly and scan measured 6 3.

It's quite common to be out by a few days to a weekish quite early on but I've never heard of a scan being out by 3-4weeks.

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