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A study  presented at the American College of Obstetricians and Gynecologists (ACOG)  57th Annual Clinical Meeting in Chicago, USA on the 13th of May 2009 reports findings of an up to 94% accurate prediction of a pregnancy outcome when a transvaginal scan is performed between Day 33 and Day 36 post-conception.

The findings were presented by lead author Soyoung Bae, MD, from the Department of Obstetrics/Gynecology, University of Toledo Medical Center in Ohio, USA. According to Dr Bae, the scan is performed to look for three markers which are presence or absence of fetal heart activity, size of the gestational sac and size of the yolk sac. A yolk sac is responsible for sustenance of the fetus at this early stage before the placenta takes over towards the end of the first trimester.

"On post-conception dates 33 to 36, gestational sac diameter of 12 mm and above, yolk sac diameter of 2 to 6 mm, and presence of fetal cardiac activity were all significantly related to successful pregnancy outcome in healthy women," Dr. Bae said. "These markers were associated with favourable pregnancy outcome even in the poor prognostic subgroups of women of advanced maternal age and those with recurrent pregnancy loss."

The study was designed as a case–control study of 1092 pregnancies, the majority of which were conceived with infertility treatments. This meant, the precise date of conception was known. The objective was to identify ultrasound markers to predict successful pregnancy in early pregnant women.

Investigators performed transvaginal ultrasound between post-conception days 33 and 36 to measure fetal cardiac activity, gestational sac diameter, and yolk sac diameter.

"On post-conception day 33 to 36, investigators found that if they could identify fetal cardiac activity, the success rate was approximately 90%. Without cardiac activity, the miscarriage rate was approximately 88%.

If the gestational sac was more than 12 mm in diameter, the pregnancy's success rate was about 92%. Crucially, if the diameter was less than 8 mm, the miscarriage rate was about 96%.

Gestational sac size diameter between 8 and 12 mm was a gray zone; the success rate was about 66% according to Dr. Bae.

The majority of yolk sac sizes were between 2 and 6 mm in diameter, and this forecast successful pregnancy in about 90% of women.

If all three markers are seen...

Thus, the presence of fetal cardiac activity, a gestational sac diameter of more than 12 mm, and yolk sac size between 2 and 6 mm in diameter were all associated with a successful pregnancy.

If all 3 markers were visible and within those stated ranges on days 33 to 36 post-conception, successful pregnancy could be predicted with 94% accuracy, Dr. Bae observed.

For the older woman

For women older than 40 years, the rate of successful prediction was 82%. For women with a history of recurrent pregnancy loss, if all 3 markers were present, the rate of accurate prediction was 94%.

This is, of course, a very exciting study and the results, if replicated in similar studies, have a real place in clinical practise especially so for women with a history of recurrent miscarriage. However, at this stage at least, it looks only applicable to those women conceiving via IVF when the precise date of conception is known.

Day 33-36 Post-Conception

Successful pregnancy outcome: 94%

Predicting a successful pregnancy outcome

Early pregnancy

Yolk sac