o_1977r8vv9vk1ts2ms0kd8pksa.pdf

a Chapter 17 Doppler Velocimetry of the Uteroplacental Circulation During Early Pregnancy 257
Fig. 17.2. Abnormal blood supply to
the placenta. Physiologic changes
(dotted areas) in some decidual segments
of spiral arteries are absent.
Myometrial segments are shown
without physiologic changes as in
preeclampsia or some cases of fetal
growth retardation. (Reprinted from
[16] with permission)
Fig. 17.3. Pulsatility indices (PI) of uteroplacental
arteries prior to delivery
plotted against the normal reference
curve (3rd, 50th, and 90th percentiles).
Cases with normal placental bed biospsies
are marked by open and closed circles,
and those with pathologic findings
are marked by stars and crosses. ThePI
values in the group with uteroplacental
insufficiency but no hypertension are
marked by encircled stars and crosses.
(Reprinted from [28] with permission)
and Doppler flow measurements [12, 24, 25] demonstrated
reduced uterine blood flow in cases of preeclampsia
and fetal growth restriction. Although
these studies were performed during late gestation, it
should be recalled that abnormal placentation begins
during the early second trimester (with the second
wave of trophoblastic invasion) or even during the
first trimester. For example, acute atherosis in the decidua,
usually found during the third trimester in
cases of preeclampsia, has also been observed during
the first trimester, from as early as 8 weeks (R. Laurini,
personal communication). It is not surprising
therefore that abnormal flow patterns (using Doppler
flow measurements) can be detected as early as the
second trimester [26, 27]. An association between abnormal
Doppler flow patterns in the uterine artery
and histomorphologic changes in the placental bed
has been demonstrated [28±30] (Fig. 17.3). However,
all studies reported a considerable overlap in the degree
of physiologic changes between normal and
complicated pregnancies. The association between
pregnancy complications and increased uteroplacental
resistance as indicated by abnormal Doppler flow
cannot then be solely explained by abnormal uteroplacental
vessel histopathology [29]. Impaired physiological
adaptation of the spiral arteries may not be
the single causal factor in preeclampsia and the concept
of heterogeneous causes of preeclampsia as was
recently suggested [31].