A twin pregnancy occurs in our community in 1 in 80 pregnancies. About seventy percent of twins are non identical – ie there would be two eggs and two sperm resulting in two separate fertilisations. The other option is where there is one egg and one sperm and subsequently the fertilised egg splits in half. This split can occur anytime between Day 1 and Day 9. If the split occurs after Day 9 the twins will be conjoined.
It is important for us to know what type of twin pregnancy an individual may have, as this may vary the management strategy.
Twin to Twin Transfusion
Twin-to-twin transfusion syndrome occurs specifically in identical twins sharing the same placenta. It is estimated to occur in 5-10% of identical twin pregnancies. In twin-to-twin transfusion syndrome, the twins share not only the same placenta but some of the same circulation. This allows the transfusion of blood from one twin (the donor) to the other (the recipient). The donor twin becomes small and anemic, and the recipient twin becomes large and overloaded with blood.
Because the recipient twin has more blood, he/she also urinates more and has more amniotic fluid. The donor twin has less amniotic fluid; sometimes there is so little fluid that the fetus appears on ultrasound to be stuck in place on the wall of the uterus (known as "stuck twin phenomenon").
Twin-to-twin transfusion syndrome can range from mild to severe. It can occur at any point during the pregnancy, even at birth (once one umbilical cord has been clamped after delivery, the other twin may get a rush of extra blood).
Symptoms of twin-to-twin transfusion syndrome may include:
In the pregnant mother - a rapidly enlarging abdomen over 2-3 weeks, as the amniotic fluid of the recipient twin builds up; premature labor, and premature rupture of membranes (water breaks early)
In the donor twin - Small for gestational age, 10-20% smaller than recipient twin, pallor (due to anemia), poor circulation
In the recipient twin - Large for gestation age, 10-20% larger than donor twin, ruddy (red) skin and jaundice (due to extra blood).
Twin-to-twin transfusion syndrome may be suspected if a pregnant woman carrying twins finds her abdomen enlarging rapidly. The syndrome can also be detected on ultrasound examination of the uterus. If the syndrome is mild, or not detected on ultrasound, the appearance of the twins at birth may identify the syndrome. Also, a complete blood cell count done after birth will show anemia in the donor twin and excess red blood cells in the recipient twin.