Introduction
Ultrasonographic assessment of fetal growth in the antenatal period is
commonplace in the United States.1-3 Evaluation
typically consists of calculation of estimated fetal weight (EFW) and
comparison against a population average to generate a percentile value,
with percentiles <10th considered small for
gestational age (SGA) and >90th as large
for gestational age (LGA).2-4 Accuracy of prediction
of morbidity from both abnormal fetal growth remains poor, probably due
to the assumption inherent in our current approach that all fetuses
share a similar growth potential.5, 6
Male newborns have long been recognized to be larger than female
newborns of the same gestational age, such that neonatal growth charts
in the United States are sex-specific.7-9 Despite
this, intrauterine growth charts remain
sex-neutral.10-13 This is true even for growth charts
that were developed in the era when fetal sex is routinely visible on
prenatal ultrasound.10, 12 A prior analysis found that
the Hadlock standard was twice as likely to consider female fetuses as
being <10th percentile compared with male
fetuses, even though female fetuses had significantly lower morbidity
than male fetuses.14, 15 Population fetal growth
standards that do not account for fetal sex, such as the Hadlock
standard, may generate disparities in diagnoses of abnormal growth
between fetal sexes that may not be justified by morbidity. Given the
knowledge of sex differences in fetal growth and the routine prenatal
assessment of fetal genitalia,1 the lack of
investigation into sex-specific intrauterine growth standards represents
an important gap in both research and clinical practice.
Therefore, our objectives were: (1) to derive a prescriptive
sex-specific fetal growth standard; (2) to compare metrics of clinical
outcomes and management according to growth status using sex-neutral
versus sex-specific growth standards in an unselected cohort.