MULTIPLE GESTATION

Incidence Spontaneous twins ~1 in 80 pregnancies Triplets ~1 in 8000 pregnancies Monozygotic twins- 3 to 5 per 1000 pregnancies with uniform frequency worldwide Dizygotic twins- variable incidence (4-50 per 1000 pregnancies) by locale, race, maternal age

Maternal Risks Hyperemesis Anemia PIH Gestational diabetes Postpartum hemorrhage Placenta previa

Fetal Risks Congenital anomalies Growth restriction of discordant twin Twin-twin transfusion Fetal demise (death of one fetus puts other at risk for DIC) Premature delivery 2nd twin: malpresentation, in utero hypoxia, hyaline membrane disease Cerebral palsy

Unique Risk of CP in Multiple Gestation Single fetal demise Zygosity and chorionicity (monochorionic) Twin-twin transfusion Growth restriction Embryonic death Mode and circumstances of delivery Fetal inflammation

Types of Twins Dizygotic (2/3): dichorionic (2 placentas) if implant sites are near, placentas may fuse yet there are no vascular connections Monozygotic (1/3): dichorionic, monochorionic, diamniotic, monoamniotic fused or separate placentas at risk for twin-twin transfusion

Most common Monochor, Diamnio Single placenta MONOZYGOTIC Rare Monochor,Monoamnio Single placenta Dichor, Diamnio Separate or fused placenta Monochor, Monoamnio Fused placenta Dichor, Diamnio Separate placenta Twins. (A), The most common type of monozygotic twinning, with division of the inner cell mass of the blastocyst resulting in separate amnions but a single chorion and placenta; (B), a rare form of monozygotic twinning, with complete division of the embryonic disc resulting in two embryos in a single amniotic sac with a single placenta and chorionic sac; (C), monozygotic twinning with division occurring between the two-cell and morula stages to produce identical blastocysts, resulting in separate amniotic and chorionic sacs and either separate (shown) or fused placentas; (D,E), dizygotic twinning, with (D) or without (E) fusion of the placenta and chorion. DIZYGOTIC

MONOZYGOTIC: Dichorionic, Diamniotic Due to early division

MONOZYGOTIC: Monochorionic, Diamniotic Highest risk of twin-twin transfusion

MONOZYGOTIC : Monochorionic, Monoamniotic Twins. (A), The most common type of monozygotic twinning, with division of the inner cell mass of the blastocyst resulting in separate amnions but a single chorion and placenta; (B), a rare form of monozygotic twinning, with complete division of the embryonic disc resulting in two embryos in a single amniotic sac with a single placenta and chorionic sac; (C), monozygotic twinning with division occurring between the two-cell and morula stages to produce identical blastocysts, resulting in separate amniotic and chorionic sacs and either separate (shown) or fused placentas; (D,E), dizygotic twinning, with (D) or without (E) fusion of the placenta and chorion. Risks: cord problems, high mortality rate

Conjoined Twins 1/200,000 births Half born stillborn   Conjoined Twins 1/200,000 births Half born stillborn More likely female ~75% Thoracopagus most common Thoracopagus:connected at the upper portion of the torso, share a heart, which makes it nearly impossible to separate them and save them both. Thoracopagus twins make up about 40 percent of all conjoined cases. Eng Bunker’s home in Surry County, NC   Return to Famous People Home

Twin-Twin Transfusion Placental vascular anastomoses Occurs in only 5-15% of monochorionic, diamniotic twins despite ~85% with vascular anastomoses Does not occur in dichorionic twins Interestingly, does not occur in monochorionic, monoamniotic twins

Vascular Anastomoses

Twin-Twin Transfusion Dx: discordant growth by ultrasound Amniotic sacs and umbilical cords Single placenta Clinical Sxs: rapid uterine growth, changes in fetal movement, preterm labor, postnatal hemoglobin difference of >5 g/dl between the twins

Twin-Twin Transfusion Recipient twin: Polycythemia Hypervolemia Polyhydramnios CHF, hydrops Hyperbilirubinemia High birthweight Donor twin: Anemia Hypovolemia Oligohydramnios Hypoglycemia “stuck twin” fetus appears stuck due to amnion adhering to fetus Decreased urine output Lower birthweight

Obstetrical Management Serial removal of amniotic fluid for polyhydramnios if > 20 weeks gestation Create an opening in amnion between the two fetuses to allow fluid exchange Laser ablation of placental vascular anastomoses (high complication rate) Selective reduction of donor twin if high risk of death for both twins

Prognosis Perinatal death rate is 9-11 times the rate for singletons Monoamniotic twins have the highest mortality rate mostly because of cord entanglement Monozygotic twins have a mortality and morbidity rate that is 2-3 times that of dizygotic twins