[Sonoembryological criteria in the evaluation of gestational age]

The progressive appearance of specific embryological structures has been successfully used to define the ultrasonographic gestational age (GA). In our study we have revised this technique by comparing our results with the ones from Warren et al. obtained in 1989. Aim of the study is to evaluate the accuracy of this technique when applied working with new instrumentations and average skilled sonographers.

Sixty-five pregnant women with correct GA ranging between 4 and 12 weeks have been observed between April 2003 and March 2004. We exposed them to an ultrasound examination looking for these structures in terms of presence/absence: gestational sac, yolk sac, embryo pole with cardiac activity, thromboencephalic cavity, falx cerebri and physiologic midgut herniation. We used transvaginal sonography (TVS) until 11 weeks of GA, from 11 weeks + 1 day we switched to transabdominal sonography (TAS). We have compared our results with the ones published by Warren et al.

Gestational sac's visualization has been possible between 4 weeks+3 days/5 weeks of GA. Yolk sac has been visualized between 5 weeks+4 days/6 weeks of GA, embryo with cardiac activity has been observed between 5 weeks+6 days/6 weeks+2 days of GA, romboencephalic cavity has been visualized between 7 weeks and 7 weeks+5 days, falx cerebri has been detected between 9 weeks+1 day/10 weeks+3 days. Visualization of physiologic midgut herniation has been possible between 8 weeks+3 days/8 weeks+6 days; it disappeared between 10 weeks+3 days/11 weeks +1 day.

Although the technological improvement in the US equipment in the last 15 years and the combination of TVS with TAS, there has been no advanced visualization of those single embryological structures. Indeed there has been a reduction of the time range during which those structures have been visualized. This improvement might have important practical implications in the ultrasonographic assessment of GA.