Elsevier

Placenta

Volume 31, Issue 9, September 2010, Pages 756-763
Placenta

First trimester placental and myometrial blood perfusion measured by 3D power Doppler in normal and unfavourable outcome pregnancies

https://doi.org/10.1016/j.placenta.2010.06.011Get rights and content

Abstract

Introduction

To evaluate whether 3D placental and myometrial power Doppler blood perfusion in the first trimester can be used to detect risk pregnancies.

Methods

3D power Doppler vascularization index (VI) and flow index (FI) of the entire placenta and the neighbouring myometrium were separately measured in the first trimester in all women with singleton pregnancies during a period of three months. In addition we measured placental volume, placental quotient, PAPP-A, as well as uterine artery at 12 and 22 weeks (mean PI and mean notch) and compared those data with the pregnancy outcome.

Results

Data from 383 women could be evaluated. 10 developed pre-eclampsia (PE). Both flow and vascularization were markedly lower in the placentas compared to the adjoining decidua and myometria. There was some correlation between placental vascularization Index (PVI) as well as deciduo-myometrial vascularization index (MVI) and placental volume, PAPP-A and number of pregnancies and a marked correlation between PVI and especially MVI to mean notch at 12 weeks and 22 weeks (PVI: −0.215, −0.274 MVI: −0.316,−0.322). PVI and MVI were significantly reduced in women with pregnancy problems and showed the greatest reduction in PE-pregnancies (p: 0.0018, 0.0004). Of all measured parameters MVI showed the best sensitivity for the detection of PE.

Conclusion

The correlation between PVI and MVI in the first trimester and mean notch in the second shows that they provide valuable information at as early as 12 weeks which normally so far is only available at 22 weeks by uterine artery Doppler flow. As MVI measures the percentage of vessels in the deciduo-myometrial area it could also provide information on trophoblast invasion. This hypothesis is supported in particular by a marked decrease of the MVI in pregnancy problems especially in PE-pregnancies.

Introduction

The causes for pregnancy-associated problems like pre-eclampsia and intrauterine growth restriction are diverse and elusive, and yet, from a clinical point of view, there seems to be an underlying basis – namely abnormally low blood flow through the placenta [1], [2], [3], [4]. A clinical example which supports this hypothesis is increased uterine artery blood flow impedance in the second trimester of pregnancy measured by 2D ultrasound Doppler. A great number of studies show a strong correlation between this condition of reduced placental blood flow, caused by an impaired trophoblast invasion, and conditions like pre-eclampsia and intrauterine growth restriction [5], [6], [7], [8], [9], [10]. When this connection was detected, it raised hope that women at risk could be treated prophylactically several weeks before the real disease starts, in order to avoid or at least mitigate any pregnancy problems. Nevertheless, it turned out that the detection of increased uterine artery impedance during the second trimester is only of limited use, as prophylactic treatment at this late stage is not sufficiently effective [11], [12], [13], [14]. At best it may lead to better pregnancy surveillance. The next logical step was to perform uterine Doppler measurements in the first trimester to start a possible treatment at this early stage. Increased uterine artery impedance in the first trimester is unfortunately not as helpful as in the second trimester as its correlation with pregnancy problems is considerably weaker [15], [16], [17], [18].

Uterine artery impedance reflects the resistance of blood flow in the decidual and myometrial spiral arteries of the mother. Fetal trophoblasts invade maternal tissue alongside these arteries, destroying their muscle fibres and thus remodelling these vessels into pliant channels, leading to low flow resistance. The activity of this process is only inadequately captured by uterine artery Doppler impedance, as trophoblast invasion starts as early as the first trimester but Doppler studies show the best result many weeks afterwards at approximately 22–24 weeks.

A possible approach to assess trophoblast invasion in the first trimester, i.e. at the time when it actually takes place, could be to measure placental and myometrial vascularization and perfusion. Power Doppler sonography is a method which allows observation of the number and flow of small tissue-vessels. It has been stated that it could be superior to spectral Doppler in low velocity blood flow conditions [19], [20]. 3D methods however can provide this information for the entire placenta and its adjoining myometrium. Some studies have focused on this particular aspect but they were mostly performed relatively late in pregnancy and the methods used were unconvincing as only parts of the placentas were measured [21], [22], [23], [24].

In this study we present data of routine 3D power Doppler measurements of the entire placenta and the neighbouring myometrium, done between 11 and 14 weeks of gestation. We want to ascertain how placental and myometrial blood flow and vascularization behave at this early stage of pregnancy. By comparing these findings with second trimester uterine artery impedance and pregnancy outcome data we want to know whether these indices can be used to assess the trophoblast activity in order to detect risk pregnancies earlier in pregnancy.

Section snippets

Methods

All women who book for delivery in our hospital routinely receive a free nuchal translucency and “combined test” measurement between 11 and 14 weeks when they give their consent. At the same time we routinely measure the placental volume (PV) with 3D ultrasound and form the placental quotient (PQ = placental volume/crown-rump length) which has repeatedly been described [25], [26], [27]. We also examine both uterine arteries at the level of the internal cervical os and calculate the pulsatility

Statistics

Associations were calculated by the non-parametric Spearman’s correlation coefficient in SAS (SAS/STAT User’s Guide, Version 9, Cary, NC 27513: SAS Institute Inc. 2002–2003). A group consisting of PE and PIH-pregnancies was formed and compared with the group of normal outcome pregnancies using the Kruskal–Wallis test. Pair-wise comparisons for all measured parameters between normal versus PE and PIH-pregnancies were done by the Wilcoxon test. P-values for those pair-wise comparisons were

Results

Placental and myometrial vascularization and flow in 423 singleton pregnancies were measured. Six had to be excluded due to fetal aneuploidies or malformations. Four women suffered from abortion between 12 and 22 weeks. 30 women did not show up at the scheduled time of fetal anomaly scan for unknown reasons or pregnancy outcome could not be followed up, which left a total of 383 women for evaluation.

Maternal data are shown in Table 1.

The correlations of the collected data to placental and

Discussion

Many attempts have been made to find first trimester parameters which are able to detect pregnancies at risk for IUGR and PE. According to a common hypothesis, these severe problems are a consequence of low placental blood flow due to impaired trophoblast invasion [1], [2], [3], [4]. Efforts have been made to assess reduced placental blood flow using uterine artery spectral Doppler. Large scale studies, however, show that the sensitivity of this method is limited if used as a screening tool in

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