o_1977r8vv9vk1ts2ms0kd8pksa.pdf

268 I. Thaler, A. Amit
Table 17.1. S/D ratio in uterine arteries during the first
and early second trimesters for singleton and twin pregnancies
Gestational age
(weeks)
S/D ratio (meanÔSEM)
Singleton Twins p
4±7 7.63 Ô0.45 6.77 Ô0.34 NS
8±11 5.56 Ô0.36 4.37 Ô0.26 < 0.01
12±15 4.60 Ô0.33 2.84 Ô0.16 < 0.0001
16±19 3.23 Ô0.15 2.38 Ô0.10 < 0.0001
NS, not significant; SEM, standard error of the mean.
Table 17.2. Total blood flow to the uterus a during the first
and early second trimester for singleton and twin pregnancies
Gestational age
(weeks)
Total blood flow (ml/min)
(mean ÔSEM)
Singleton Twins p
4±7 237.6 Ô 6.15 242.8 Ô7.19 NS
8±11 251.2 Ô 7.12 300.0 Ô8.96 < 0.0001
12±15 279.0 Ô 7.19 343.4 Ô7.73 < 0.0009
16±19 323.4 Ô 8.07 391.4 Ô8.69 < 0.0002
NS, not significant; SEM, standard error of the mean.
a Sum of flows in both uterine arteries.
Table 17.3. Frequency and magnitude of difference of PI
between left and right uterine arteries of normal pregnancies
at 8±13 weeks' gestation (from [91] with permission)
Fig. 17.19. Reference ranges (mean Ô2 SD) and individual
values of systolic/diastolic (S/D) ratio from both main uterine
arteries (top), arcuate arteries (middle), trophoblastic
vessels (bottom). (Reprinted from [27] with permission)
tween left (L > R) and right (R > L) predominance for
both PI and RI values. On average there appeared to
be no difference between the left and right uterine arteries.
The most likely explanation for the difference
in the PI or RI between the left and right uterine arteries
is that changes in down-stream impedance in
the uterine artery supplying the placenta precede
those in the uterine artery on the nonplacental side of
the uterus. As clear delineation of the placenta is often
impossible during early gestation, one can only
assume about the relation between the resistance to
flow and placental location at this stage of gestation
[91]. Some investigators prefer to calculate the mean
RI or PI of both sides of the uterus, which would indicate
the total downstream impedance [85, 90, 91].
Gestation
(weeks)
Differences in PI
No. L > R No. R >L R = L
(No.)
8 7 0.64 Ô0.37 6 0.86 Ô0.67 ±
9 3 0.27 Ô0.24 4 0.35 Ô0.23 2
10 5 0.50 Ô0.39 4 0.60 Ô0.32 1
11 5 0.54 Ô0.31 5 0.53 Ô0.33 ±
12 12 0.48 Ô0.59 12 0.51 Ô0.30 2
13 8 0.60 Ô0.24 9 0.43 Ô0.40 2
Results are means ÔSD of the differences between the left
uterine artery (L) and right uterine artery (R).
L >R, left predominance; R >L, right predominance; R, L indicates
no predominance.
When using the transvaginal pulsed Doppler technique
the intraobserver coefficient of variation ranged
between 7.6% [84] and 9.0% [14]. The reported range
for the continuous-wave Doppler method was between
4.0% [13] and 5.6% [91].