what-when-how
In Depth Tutorials and Information
contemplating a pregnancy. In addition, patients may
benefit from an open conservation about reproductive
choices including interrupting an affected pregnancy,
use of
in vitro
fertilization and selection of non-affected
embryos.
51
Further, nonassertive mating is common
in individuals with short stature. This can complicate
pregnancy counseling regarding predicting outcomes
and natural history in individuals with compound het-
erozygosity for two dominant mutations affecting the
skeleton.
In affected fetuses, the mineralization, size and shape
of the hands and feet are normal, though equinovarus
is commonly seen in severely affected fetuses. This
finding of normally mineralized hands and feet helps
differentiate perinatal lethal OI from autosomal reces-
sive hypophosphatasia, a rare autosomal recessive
disorder that also presents with an undermineralized
fetal skeleton.
56
The prenatal presentation of OI can be
quite variable, especially in the third trimester, from
mild bowing to multiple long bone fractures. There are
other skeletal disorders that present with bending and
bowing in the prenatal period,
57
but these can be distin-
guished based on differing ultrasound findings.
The initial management decisions after identifying
a fetus with findings consistent with OI include deter-
mining if perinatal lethality is likely and establishing
a definitive diagnosis if possible. Perinatal lethality
can be difficult to precisely determine but includes
diminished femur length to abdominal circumference
of <0.16,
58
suggesting the likelihood of pulmonary
hypoplasia in the newborn period. Obtaining material
for DNA diagnosis via invasive testing confirms the
diagnosis and helps many families with their decision-
making, particularly if the ultrasound findings do not
appear definitive. DNA diagnosis can also help iden-
tify mutations that have been previously reported with
a clinical phenotype, thus allowing families to make
decisions with a better understanding for natural
history.
Fetuses with perinatal lethal OI tend to present in the
third trimester with polyhydramnios and malpresenta-
tion (breech) though these are not uniform findings.59
59
Similarly to caring for a severely affected pregnant OI
patient, a team approach to maternal-fetal manage-
ment is indicated. Patients who choose to continue the
gestation until term should meet in advance with the
pediatricians and neonatologists who will assess
the newborn after delivery and make post-delivery
management plans. Obstetrical management decisions
include whether preterm labor should be treated, how
aggressively, and mode of delivery for a fetus with a
potentially guarded prognosis.
For fetuses predicted to have nonlethal forms of OI,
a team approach including those caring for the mother
and fetus is indicated. Mode of delivery should be
based on maternal and fetal indications. There is con-
troversy over whether a fetus with congenital anoma-
lies, including OI, should be delivered by cesarean
section to optimize outcome. However, data suggest
that the number of newborn fractures is not different
between fetuses delivered vaginally versus by cesarean
section.
60
Thus, decisions regarding delivery and inter-
vention should be made by the pregnant patient and
her physicians based on the constellation of issues for
that pregnancy.
ULT
RASOUND DIAGNOSIS OF
OI
OI was one of the first skeletal disorders to be diag-
nosed by prenatal ultrasound.
52
Most cases of OI rec-
ognized in the prenatal period occur in patients with
no family history of OI. There is also a bias toward
diagnosis of the more severe forms because routine
ultrasound screening for congenital anomalies usually
occurs in the late second trimester.
53
Nonlethal forms
of OI more frequently present in the third trimester or
the newborn period and are often not detected in the
prenatal period. The ultrasound findings for autosomal
dominant and recessive forms of perinatal lethal OI (OI
type II, Sillence classification)53
53
are listed in
Table 26.1
.
The findings include poor mineralization of the calvar-
ium, well-visualized intracranial structures, flattened
facies, small chest, short ribs with and without frac-
tures, and variably bent, bowed and fractured appen-
dicular bones
54
(
Figures 26.2 and 26.3
). Postnatally,
radiographic lateral views of the spine show osteope-
nia, but this is not appreciated by
in utero
ultrasound.
TABLE 26.1
Ultrasound findings in Osteogenesis Imperfecta
Poorly or absent mineralization of the calvarium
Well-visualized intracranial structures
Calvarium deformation from ultrasound probe pressure
Flattened facial profile
Absent mineralization of facial bones
Flattened chest on sagittal view
Circumferential view - heart circumference greater than 50% of the
chest
Rib factures - ultrasound areas of hyper and hypoechogenicity
Wavy appearing ribs - circumferential views
Variably number of bent/bowed/fractured long bones
Lower extremities affected > upper extremities
Equinovarus
Normal appearing hands and feet
Occasional polyhydramnios
