Correct statement about establishing the chronicity in twin pregnancy is: (AIPG 2010)
|A||Same sex rule out dichorniocity|
|B||Twin Pick sign in dichorniocity|
|C||Thick membrane is present in monochorion|
|D||Best detected after 16 weeks|
Twin Pick sign in dichorniocity
1. We can determine chorionicity and amnionicity in two periods during gestation: in the first trimester and in late second and third trimesters
2. There is no doubt that the assessment in the early first trimester of pregnancy is superior to late examinations.
3. Chorionicity refers to the identification of the number of chorionic sacs, and amnionicity refers to the number of amniotic sacs. In the first trimester, using transvaginal sonography (TVS) one can determine the chorionicity as early as the 4th to 5th postmenstrual week, when the chorionic sacs are visualized and their number counted.
4. They appear as round sonolucent structures surrounded by hyperechogenic chorion.
5. The yolk sacs may be observed within each chorionic sac.
6. Also, the number of embryos can be measured by 6 postmenstrual weeks.
7. In the 2nd and 3rd trimesters, accurate establishment of chorionicity and amnionicity is difficult although possible. In some instances this becomes absolutely impossible with advancing gestation.
The sonographic criteria for diagnosing chorionicity and amnionicity in the 2nd and 3rd trimesters include:
1. Determination of fetal gender – different gender indicates dizygotic twins, same gender may be monozygotic in 25% of cases;
2. The number of placental sites is important: two separate placental sites indicate dichorionic placentalization. A single or fused placenta is more difficult to evaluate;
3. The interfetal membrane should be assessed for membrane origin, thickness and the number of layers.
4. In dichorionic twins, the area of fusion between the placentas form a wedge-shaped zone termed the “Lamda” or “twin-peak“ sign In monochorionic twins, this structure is absent and the junction between the two amniotic sacs and the uterine wall creates a T-shaped appearance.
5. Counting the number of layers and measurement of their thickness is of importance: in monozygotic twins there are only two membranes which are thin as opposed to 4 layers and thick membranes in dizygotic twins.