# Dating accuracy

With transvaginal ultrasound, checking for embryonic development known to occur within a certain time frame more accurately dates a pregnancy.

Transvaginal ultrasound can see embryonic development about a week before transabdominal ultrasound, the American Pregnancy Association (APA) states.

Sometimes a trans-vaginal examination shows that your pregnancy is less advanced than expected.

The earlier the ultrasound is done, the more accurate it is at estimating the baby's due date.

This is because the fetus is growing so quickly that there is a big difference in size from week to week.

Also the fetus cannot bend and twist too much yet, so the length of the body is fairly constant.

Perkins also has extensive experience working in home health with medically fragile pediatric patients.

) the fetus is clearly seen on trans-vaginal ultrasound and the heart beat can be seen at this early stage (90 to 110 beats per minute under 6 to 7 weeks, then 110 to 200 beats per minute as the baby matures).If you have any questions about this, please feel free to talk to your sonographer or doctor about it.A registered nurse with more than 25 years of experience in oncology, labor/delivery, neonatal intensive care, infertility and ophthalmology, Sharon Perkins has also coauthored and edited numerous health books for the Wiley "Dummies" series.Ultrasounds performed during the first 12 weeks of pregnancy are generally within 3 - 5 days of accuracy.The most accurate time is between 8 and 11 weeks gestation.Carbon 14 is a form of carbon which decays exponentially over time.The amount of Carbon 14 contained in a preserved plant is modeled by the equation  f(t) = 10\left(\frac\right)^.The range of years 30 \pm 40$gives a certain probability (about$ percent) that half of the Carbon $will decay during this span of years: it is of course possible that the actual half life could be shorter or longer.Each given sample of Carbon$ would have to be treated individually on an experimental basis and if many experiments were conducted, an expected $percent would give a half-life measured between 90$ and 70\$ years.These scans are only used to estimate the due date of your baby if this is all you have to go on.If you have more than one ultrasound during your pregnancy, giving you 'multiple dates', then the earliest ultrasound estimate should be used, because it will be more accurate.