Diagnostic ultrasound ( PDFDrive )

1454 PART IV Obstetric and Fetal Sonography
predictive value (PPV) of up to 51% for LGA and 67% for
macrosomia. Other proposed sonographic parameters have lower
sensitivity or lower PPV than the estimated fetal weight 62,103,106,116-124
(Table 42.11).
Diabetic Mothers
Fetuses of insulin-dependent and gestational diabetic mothers
are exposed to high levels of glucose throughout pregnancy and,
as a result, produce excess insulin. his leads to overgrowth of
the fetal trunk and abdominal organs, while the head and brain
grow at a normal rate. 104,105 herefore these fetuses tend to have
diferent body proportions than fetuses of nondiabetic mothers.
Sonographic measurements of fetuses of diabetic mothers
demonstrate accelerated growth of the fetal thorax and abdomen
beginning between 28 and 32 weeks’ gestation. 104,105,125
An LGA weight occurs in 25% to 42% and macrosomia in
10% to 50% of infants of diabetic mothers. 104,105,126 As many as
12% of infants of mothers with diabetes weigh more than 4500 g
at birth. Perinatal complications are more frequent in macrosomic
fetuses of diabetic mothers than in those of nondiabetic
mothers. 109,113,114,127,128 Shoulder dystocia, for example, occurs in
31% of macrosomic fetuses of diabetic mothers and only 3% to
10% of macrosomic fetuses of nondiabetic mothers. 110,113
Many sonographic parameters, involving a variety of measurements,
formulas, and ratios, have been proposed for diagnosing
LGA and macrosomia in the fetus of the diabetic mother 117,129-131
(Table 42.12). As a group, these have higher sensitivities and
PPVs than sonographic criteria in the general population, in
part because of the higher prevalence of large fetuses in diabetic
mothers.
As in the general population, the most straightforward
approach to diagnosing LGA and macrosomia in the fetuses of
diabetic mothers is by means of the sonographically estimated
fetal weight. 68,117,129,132,133 A fetus whose estimated weight falls
above the 90th percentile for gestational age has a 74% likelihood
of being LGA, versus 19% if the estimated weight lies below the
90th percentile. 129 A weight estimate above 4000 g is associated
with a 77% chance of macrosomia, and one above 4500 g with
an 86% chance. he chance of macrosomia is only 16% when
the weight estimate is less than 4000 g. 68 hus, if vaginal delivery
is believed to be contraindicated for the macrosomic fetuses of
diabetic mothers, the estimated fetal weight should be considered
when selecting the route of delivery.
The Small-for-Gestational-Age Fetus
and Fetal Growth Restriction
Fetuses are termed small for gestational age (SGA) if their estimated
weights are below the 10th percentile for gestational age.
SGA fetuses are a heterogeneous group and can be subdivided
into constitutionally small fetuses (e.g., those with small parents)
and fetuses whose small size is due to a pathologic process.
Small-for-Gestational-Age Fetuses: Causes
CONSTITUTIONALLY SMALL
PATHOLOGICALLY SMALL
Placenta Mediated
Primary placental
Maternal
Fetal
Aneuploidy
Malformations
Infections
TABLE 42.11 Sonographic Criteria for Large-for-Gestational Age (LGA) and Macrosomia in
the General Population: Performance Characteristics
(%) PREDICTIVE VALUES (%) a
Sensitivity Speciicity Positive Negative
CRITERIA TO PREDICT LGA a
Elevated AD-BPD 115 46 79 19 93
Low FL/AC 103,115 24-75 44-93 13-26 92-94
Elevated AFV 119,123 12-17 92-98 19-35 91
Elevated ponderal index 103,115 13-15 85-98 13-36 91-94
High EFW 103,123 20-74 93-96 6-51 88-94
Elevated growth score 103 14 91 10 90
Elevated AFV, high EFW 123 11 99 54 99
CRITERIA TO PREDICT MACROSOMIA
Elevated FL 121 24 96 52 88
Elevated AC 121 53 94 63 89
High EFW 63,124,121 11-65 89-96 38-67 83-91
Elevated BPD 121 29 98 71 92
a Predictive values for criteria for LGA computed using Bayes’ theorem,112 assuming an LGA prevalence rate of 10%.
AC, Abdominal circumference; AD, abdominal diameter; AFV, amniotic luid volume; BPD, biparietal diameter; EFW, estimated fetal weight; FL,
femur length; FL/AC, femur length to abdominal circumference ratio.
With permission from Doubilet PM, Benson CB. Fetal growth disturbances. Semin Roentgenol. 1990;25(4):309-316. 117