Which is the most common cause of discordant growth in a monochorionic gestation?

Which is the most common cause of discordant growth in a monochorionic gestation?

• A. Twin-Twin Transfusion Syndrome
• B. Intrauterine growth restriction
• C. Anemia
• D. Placental insufficiency

Answer: (A)

In monochorionic pregnancies the twins share one placenta with intertwin blood vessels, so blood can flow directly between them. The most common reason for one twin to grow more slowly than the other is Twin-Twin Transfusion Syndrome, which happens when those placental vessels create an unbalanced transfer of blood from one twin (the donor) to the other (the recipient). This causes the donor to become relatively volume-depleted, with reduced urine output and growth restriction (often accompanied by oligohydramnios), while the recipient becomes overfilled with blood and fluids, which can lead to excess urine production and sometimes polyhydramnios. The result is discordant growth driven by the unequal placental blood flow. While intrauterine growth restriction can cause growth differences in any pregnancy, TTTS is the most common cause specifically in monochorionic placentation because of the shared vascular connections. Anemia or placental insufficiency may occur in this context but are not the initiating cause of the discordant growth seen in TTTS.

In monochorionic pregnancies the twins share one placenta with intertwin blood vessels, so blood can flow directly between them. The most common reason for one twin to grow more slowly than the other is Twin-Twin Transfusion Syndrome, which happens when those placental vessels create an unbalanced transfer of blood from one twin (the donor) to the other (the recipient). This causes the donor to become relatively volume-depleted, with reduced urine output and growth restriction (often accompanied by oligohydramnios), while the recipient becomes overfilled with blood and fluids, which can lead to excess urine production and sometimes polyhydramnios. The result is discordant growth driven by the unequal placental blood flow. While intrauterine growth restriction can cause growth differences in any pregnancy, TTTS is the most common cause specifically in monochorionic placentation because of the shared vascular connections. Anemia or placental insufficiency may occur in this context but are not the initiating cause of the discordant growth seen in TTTS.