Scope of the Problem:

Probably the single largest clinical problem facing perinatal medicine today
Related to satisfying the popular desire for fertility
Dramatic increase since 1980
Substantial contributor to both prematurity rate and NICU days
About 1/7 preterm births
Almost 1/4 of births <32 weeks
Estimated near a quarter of NICU days
Twins and more may represent 1/4 of pregnancies from OI and ART
80% of triplets come from OI and ART

According to the March of Dimes mortality/morbidity rates increase among multifetal pregnancies

Characteristics	Twins	Triplets	Quadruplets
Average birth weight	2.3 kg	1.6 kg	1.3 kg
Average gestational age at delivery	35.3 wks	32.2 wks	29.9 wks
% requiring admission to neonatal intensive care unit (NICU)	25%	75%	100
Average length of stay in NICU	18 days	30 days	58 days
% with growth restriction	14-25%	50-60%	50-60%
% with major handicap	-	20%	50%
Risk of cerebral palsy (CP)	4Xs higher than singletons	17Xs higher than singletons	No data available
Risk of death by age 1 year	7Xs higher than singletons	20Xs higher than singletons	No data available

Chorionic/ Amniotic Sharing

The amniotic sac is thin pair of membranes, which hold the developing embryo until shortly before birth. The inner membrane, the amnion, contains the amniotic fluid and the fetus. The outer membrane, the chorion, contains the amnion and is pressed against the the lining of the uterus.

Multiple pregnancies sometimes share the amnion and the chorion. A monoamniotic pregnancy is when the embryos or fetuses are located within the same amnion which is itself in one chorion (monochorionic). A diamniotic pregnancy is when there are more than one amnion inside one chorion. If each fetus has its own chorion the pregnancy is referred to as dichorionic. Identical twins could have any of these configurations while we would expect the majority of fraternal or non-identical twins to be dichorionic and diamniotic.

Sharing the same amnion (or the same amnion and placenta) can cause complications in pregnancy. For example, the umbilical cords of monoamniotic twins can become entangled, reducing or interrupting the blood supply to the developing fetus. Monochorionic twins, sharing one placenta, usually also share the placental blood supply. In rare cases, blood passes disproportionately from one twin to the other through connecting blood vessels within their shared placenta, leading to twin-to-twin transfusion syndrome.

Chorion Sharing Risk:

• Increases risk of twin to twin transfusion syndrome
• May lead to unusual anomalies
• Occurs in probably greater than 3% of pregnancies conceived via artificial reproductive technology and ovulation induction (compared to <.5% in the general population)

Birth Defect Risks:

• If the mother is of advanced maternal age (AMA), which is greater than 35 years of age at delivery, then the Down syndrome is multiplied
• General birth defect risk of 3-5% in singleton becomes 6-10% in twins and 9-15% in triplets
• True incidence of birth defects in multifetal pregnancies is probably exceeds the above
• Monozygotic twinning increases defect risk

Screening for Birth Defects:

• Nuchal translucency - approximately 11 weeks
• Anatomic survey - approximately 18 weeks
• Focused testing based upon family history