148 Maternal Twins and Male Gender Bias in Autism Spectrum Disorders
wall of the womb, so called “stuck twin.” The recipient twin, meanwhile, will
struggle with opposite concerns. Too much blood will lead to excess urine pro-
duction, resulting in a huge bladder and accumulation of fluid, a prenatal form
of heart failure. Excess urine will increase the amniotic fluid around the recipi-
ent twin and cause the womb to over‐expand. If TTTS is untreated, premature
labor and delivery often results, with the possible loss of one or both babies.
If just one of the twins survives, that twin is at risk of brain and other organMonoamniotic monochorionic Diamniotic dichorionic (fused)Diamniotic monochorionic Diamniotic dichorionic (separated)Figure 6.4 Monochorionic monoamniotic twins have no separating membrane. They share
a placenta and share an amniotic sac. Monochorionic diamniotic twins share the same
placenta but have a separating membrane of amnion. Dichorionic diamniotic twins have a
separating membrane consisting of both chorion and amnion. They may have separated or
fused placentae. In each case, the blood flow would be unequal that may result in
discordant monozygotic twins (see text). As shown, in each case the two monozygotic twins
are receiving slightly different amounts of blood supply, making the ones on the left slightly
more vulnerable to environmental factors than the ones on the right. Source: http://www.
babymed.com/twins/twins‐monozygotic‐vs‐dizygotic‐and‐monochorionic‐vs‐dichorionic.
Adapted from Dr Amos Grunebaum.