Diagnostic ultrasound ( PDFDrive )

1040 PART IV Obstetric and Fetal Sonography
outcomes. Only a few clinical studies describe routine scan, 131
irst-trimester scan, 132 particularly, nuchal translucency screening,
133 as well as Doppler 132 and three-dimensional (3D)/fourdimensional
(4D) ultrasound. 134 Furthermore, although some
studies address the issue of repeat scans, 135,136 it was not as an
analysis of potential cumulative efects for which no information
is available.
Birth Weight
In one oten-quoted study of more than 2000 infants, a small
(116 g at term) but statistically signiicant lower mean birth
weight was found in the half exposed to ultrasound compared
with the nonexposed group. 137 However, information was collected
several years ater exposure, with no indications known and no
exposure information available. Moreover, in a later study, the
authors concluded that the relationship of ultrasound exposure
to reduced birth weight may be caused by shared common risk
factors, which lead to both exposure and a reduction in birth
weight, 138 an association but not a causal relationship.
A twice-greater risk of low birth weight was reported in another
retrospective study ater four or more exposures to diagnostic
ultrasound. 14 hese results were not reproduced in another
retrospective study with a large population, originally of 10,000
pregnancies exposed to ultrasound matched with 500 controls
and with 6-year follow-up. 139 No increased congenital malformations,
chromosomal abnormalities, infant neoplasms, speech or
hearing impairment, or developmental problems were observed
in this latter study.
In a randomized controlled trial of more than 2800 pregnant
women, about half received ive ultrasound imaging and Doppler
low studies at 18, 24, 28, 34, and 38 weeks of gestation, and half
received a single ultrasound imaging at 18 weeks. 122 An increased
risk of intrauterine growth restriction was detected in those
exposed to frequent Doppler ultrasound examinations, possibly
through efects on bone growth. However, when children were
examined at 1 year of age, there were no diferences between
the study and control groups. In addition, ater examining their
original subjects ater 8 years, the investigators found no evidence
of adverse neurologic outcome. 136 Similarly, other randomized
studies found no harmful efect of one or two prenatal scans on
growth. 140,141 Curiously, in some studies, birth weight was slightly
higher in the scanned group, but not signiicantly, except in one
group of newborns exposed to ultrasound in utero who weighed
on average 42 g (75 g in reported smokers) more than the control
group. 141 hus ultrasound exposure in utero does not appear to
be associated with reduced birth weight, although Doppler
ultrasound exposure may have some risks. 114
Delayed Speech
To determine if an association exists between prenatal ultrasound
exposure and delayed speech in children, Campbell et al. 123 studied
72 children with delayed speech and found a higher rate of
ultrasound exposure in utero compared with the 144 control
subjects. However, this retrospective study used records more
than 5 years old, with neither a dose-response efect nor any
relationship to time of exposure. A much larger study of more
than 1100 children exposed in utero and 1000 controls found
no signiicant diferences in delayed speech, limited vocabulary,
or stuttering. 142
Dyslexia
Dyslexia has been extensively studied. Stark et al. 125 compared
more than 4000 children (ages 7-12 years) exposed to ultrasound
in utero to matched controls, analyzing outcome measures at
birth (Apgar scores, gestational age, head circumference, birth
weight, length, congenital abnormalities, neonatal/congenital
infection) or in early infancy (hearing, visual acuity/color vision,
cognitive function, behavior). No signiicant diferences were
found, except for a signiicantly greater proportion of dyslexia
in children exposed to ultrasound. Given the design of the study
and the presence of several possible confounding factors, the
authors indicated that dyslexia could be incidental.
Subsequently, long-term follow-up studies of more than 600
children with various tests for dyslexia (e.g., spelling, reading)
were performed. 143-147 End points included evaluation for dyslexia
along with examination of nonright-handedness, said to be
associated with dyslexia. No statistically signiicant diferences
were found between ultrasound-exposed children and controls
for reading, spelling, arithmetic, or overall performance, as
reported by teachers. Speciic dyslexia tests showed similar
incidence rates among scanned children and controls in reading,
spelling, and intelligence scores and no discrepancy between
intelligence and reading or spelling. herefore the original inding
of dyslexia was not conirmed in subsequent randomized controlled
trials. It is considered unlikely that routine ultrasound
screening can cause dyslexia.
Nonright-Handedness
A possible link between prenatal exposure to ultrasound
and subsequent nonright-handedness at age 8 to 9 years in
children exposed to ultrasound in utero was irst reported
in 1993 from Norway. 146 According to the authors, however,
the diference was “only barely signiicant at the 5% level”
and was restricted to boys. 148 A second group of researchers
(including Salvesen, main author of the irst study), studying
a new population of more than 3000 children from Sweden,
reported similar indings of a statistically signiicant association
between ultrasound exposure in utero and nonright-handedness
in males. 129 An intriguing recent study showed that fetuses
self-touched their faces more oten with the let hand than the
right, as observed by ultrasound, in correlation to stress levels
of the mother. 149 Furthermore, laterality is, mostly, genetically
determined 150 but could, naturally, be modiied by external
factors. Evidence is insuicient to infer a direct efect on brain
structure or function, or even that nonright-handedness is an
adverse efect.
Neurologic Development and Behavioral Issues
Neurons of the cerebral neocortex in mammals, including humans,
are generated during fetal life in the brain proliferative zones
and then migrate to their inal destination by following an
inside-to-outside sequence. his neuronal migration occurs in
the human fetal brain mainly from 6 to 11 weeks of gestation 151
but continues until 32 weeks. It has long been theorized that