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MS WordPerinatologist Corner - C.E.U/C.M.E. Modules
Twins: Antepartum assessment and Intrapartum management
Sponsored by The Indian Health Service Clinical Support Center
3 Twin Pregnancy: Double Trouble?
Step 3. Initial Work-up
ULTRASOUND
So, dichorionic twins are at lower risk; how do we determine sonographically whether we have dichorionic or monochorionic twinning? The earlier in gestation you obtain the ultrasound, the easier it usually is to tell the chorionicity. Many dichorionic placentas are separate, one being anterior and the other posterior; that makes it easy. (Monteagudo) Many are fused however, making you wonder if the single placental mass implies monochorionicity. The most reliable way to detect dichorionicity in this situation is “ the twin peaks sign”,
also known as the “lambda” or the “delta” sign. Placental tissue will dissect up between the two chorio-amnions resulting in the typical wedge-shaped appearance that gives it away (Figure 1) . Monochorionic placentas on the other hand, will not demonstrate any “twin peaks”, but rather will have a “T-sign” where the thinner inter-twin membrane inserts into the placental surface. Sometimes it is difficult to see the thin wispy separating membrane, resulting in the commonly false positive diagnosis of monoamniotic twins. High resolution equipment can usually settle this question, which is important clinically because of the heightened monitoring required in the latter situation. Of course, if the twins are of disparate genders, you know they must be dichorionic, but the converse doesn’t hold.
