Læknablaðið - 15.11.1987, Page 16

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LÆKNABLAÐIÐ
NÝR DOKTOR í LÆKNISFRÆÐI - REYNIR TÓMAS GEIRSSON
Fyrir nokkru varði
Reynir Tómas Geirsson
doktorsritgerð sína
sem heitir Intrauterine
volume in pregnancy.
Hér fer á eftir
útdráttur úr retgerð
hans:
Intrauterine volume, a three dimensional measure
of growth, was evaluated in pregnancy. The
ultrasonic method for measurement of volume
was investigated for accuracy and error potentials
and then used to collect information on the
growth of three volume components, total
intrauterine (IUV), intraamniotic (IAV) and
placental volume (PLAV), in the latter half of
normal pregnancy. Against reference standards
from the normal population, two other main
groups, a nonselected and a preselected high-risk
group were studied, to test the hypothesis that a
small intrauterine volume would predict the
presence of a small-for-dates and possibly
compromised baby.
In a phantom model situation a method based on
serial paralell planimetric area (PPA)
measurements was significally more accurate than
a linear measurement method used by previous
authors. With the former method 93.3% of
measurments were within 5% of the true volume
(mean error 0.43%). Accuracy in vivo was
evaluated in 14 women undergoing midtrimester
termination and in eight women delivering near
term. High correlation between ultrasonically and
directly/indirectly measured IAV was shown.
Therefore the same level of accuracy could be
expected in pregnancy as in the phantom models.
Intraand interobserver variation was small. The
PPA method was used for all measurements in
pregnancy.
Data from 115 healthy women with no pregnancy
complications were evaluated longitudinally to
study normal growth and derive reference
standards. Median and mean values of IUV
increased from around 1000 ml at 20 weeks to
4500 ml at 40 weeks, IAV from 700 to 3400 ml
and PLAV from 260 to 800 ml during the same
times. The standard deviation was large for all
volumes at any stage of pregnancy. The rate of
volume increase was near constant for IUV and
IAV, except during the 30-35 week period when a
faster rise was observed. PLAV growth decreased
after 30 weeks. With growth of IUV and IAV
following a largely linear trend, a tendency for
ranking of volume levels was observed.
Predictability of one measurement on the basis of
earlier ones weakened with increasing separation
of time points.
In a non-selected antenatal population of 362
women having measurements at around 32 and
for most also at 36 weeks, the efficacy of volume,
fetal biparietal and abdominal area (AA)
measurements of = < lOth centile in predicting
birthweight of = < lOth and = <3rd centiles was
evaluated. IUV showed the highest sensitivity in
predicting both birthweight categories, but a
higher number of false positive tests resulted in a
lower predictive value of positive test (mean 34%
for babies weighing = < lOth centile) and a higher
at risk group than found for AA measurements
(mean 54%). IAV, PLAV and BPD had poorer
predictive values than IUV or AA.
In a preselected high-risk population of 130
women with a 30% prevalence of small-for-dates
babies, AA and IUV had the highest sensitivity
and positive predictive values. Higher sensitivity
of IUV at earlier gestations was a diagnostic
advantage. For screening purposes AA
measurements were more suitable.
Several more maternal and fetal variables,
including smoking, were not or only weakly
correlated to intrauterine volume components.
Volumetric growth in twin pregnancies and
pregnancies complicated by diabetes or
hydramnios was described. Maximum distension
of the uterus measured amounted to 8386 ml. A
link between volume levels and blood sugar
control was demonstrated.