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 commonMonochor, DiamnioSingle placenta

RareMonochor,MonoamnioSingle placenta

Dichor, DiamnioSeparate or fusedplacenta

Monochor, MonoamnioFused placenta

Dichor, DiamnioSeparate placenta

MONOZYGOTIC

DIZYGOTIC

MONOZYGOTIC: Dichorionic, Diamniotic

MONOZYGOTIC: Monochorionic, Diamniotic

Highest risk of twin-twin transfusion

MONOZYGOTIC : Monochorionic, Monoamniotic

Risks: cord problems, high mortality rate

Conjoined Twins

• 1/200,000 births

• Half born stillborn

• More likely female ~75%

• Thoracopagus most common

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