Anemia of Prematurity - Portal Neonatal

o While some placental studies suggest fewer (rather than more) vascular anastomoses
with resultant trapping of blood in the recipient fetus, other placental studies
demonstrate excessive and abnormal placental vascular communications.
Velamentous cord insertion is much more common in those fetuses with large shunts.
Curiously, the recipient (polycythemic) twin usually develops hydrops, not the (anemic)
donor. Even more curiously, death of the hydropic twin (whether untreated and/or
spontaneous, following fetal therapy, or after selective feticide) is not uncommonly
followed by the development of hydrops in the remaining twin.
o Reasons for all these events remain causes for speculation. Definitive diagnosis also is
surprisingly difficult, since hydrops may occur in either (or both) twin, disparities in fetal
size may not be present, and fetal hemoglobin or hematocrit levels may be well outside
the reference range (high or low) in the absence of any hydrops.
o Ultrasound evidence of same-sex twins, a monochorionic placenta, with hydramnios in
one sac and oligohydramnios in the other sac, often is used to make the diagnosis.
These findings and disparities in fetal sizes (15-25%) are useful, but unfortunately they
are not definitive. Determination of fetal hemoglobins by cordocentesis is employed;
however, differences in fetal hemoglobin concentration exceeding 5 g/dL are common
in the absence of hydrops, and, conversely, differences less than this may be found in
individuals with hydrops.
o Significant differences in serum protein levels also may be observed in twins with
hydrops fetalis, and atrial natruretic factor concentrations usually are high.
Unfortunately, none of these findings are diagnostic. Clearly, earlier and more precise
fetal diagnostic methods, which measure degree of functional dysfunction, are needed.
Most promising in this regard are pulsed Doppler ultrasound measurements of umbilical
vessel blood velocity. Such studies hold promise of providing an earlier window of
opportunity for fetal diagnosis and treatment. Outcome is surprisingly poor in this
condition. Most twins with hydrops die before birth (42-86%), and a shocking proportion
of survivors of the condition have cardiovascular and neurologic damage. Ultrasound
studies demonstrate cerebral white matter damage, suggesting antenatal necrosis in
approximately one third. Follow-up studies of neurodevelopment suggest serious
impairment in approximately one quarter of surviving twins.
o Many (if not most) surviving twins have significant cardiomyopathy (predominantly
right-sided), usually associated with pulmonary outflow obstruction; pulmonary artery
calcification and endocardial fibroelastosis also are common. Neutropenia, impaired
fetal growth, reduced bone density, and mineralization have been observed in the
surviving donors. Optic nerve hypoplasia has been reported, and peripheral vascular
ischemic necrosis with gangrene of distal extremities has been observed in several
individuals with the condition. Coagulopathy and embolic phenomena were speculated
in many early studies; however, scant evidence for them exists in recent reports. Very
premature delivery is common and contributes undoubtedly to the morbidity and
mortality.
o Treatment successes have been reported with transfusion of the anemic fetus,
plasmapheresis of the polycythemic twin, laser ablation of placental vascular
anastomoses, and amnioreduction; however, failures and serious complications also
have been reported with each of these.
• Cardiovascular problems causing or associated with hydrops are summarized in Table 2.
While extensive, the list is inevitably incomplete as new associations are reported each
year.