Resistance in uterine spiral arteries has also been measured. Impedance was higher in peripheral than in central vessels-a "ring-like" distribution (Matijevic, 1999). Mean resistance values were greater in all women with preeclampsia compared with those in normotensive controls. One study used MR imaging and other techniques to assess placental perfusion ex vivo in myometrial arteries removed from women with preeclampsia or fetal-growth restriction (Ong, 2003). In both conditions, myometrial arteries exhibited endothelium-dependent vasodilatory response. Moreover, other pregnancy conditions are also associated with increased resistance (Urban, 2007). One major adverse efect, fetal-growth restriction, is discussed in Chapter 44 (p. 847).
de Almeida Pimenta and colleagues (2014) assessed placental vascularity using a three-dimensional power Doppler histogram and described a placental vasculariy index. This index value was reduced in women with any pregnancy-associated hypertensive disorders-1l.1 percent compared with 15.2 percent in normal controls.
Despite these indings, evidence for compromised uteroplacental circulation is found in only a few women who go on to develop preeclampsia. Indeed, when preeclampsia develops during the third trimester, only a third of women with severe disease have abnormal uterine artery velocimetry (Li, 2005). In a study of 50 women with HELLP syndrome, only a third had abnormal uterine artery waveforms (Bush, 2001). In general, the extent of abnormal waveforms correlates with severity of fetal involvement (Ghidini, 2008; Groom, 2009).
Various biological markers implicated in the preeclampsia syndrome have been measured to help predict its development. Although most have been evaluated in the irst half of pregnancy, some have been tested as predictors of severity in the third trimester (Chaiworapongsa, 2013; Lai, 2013; Mosimann, 2013). Others have been used to forecast recurrent preeclampsia (Demers, 2014; Eichelberger, 2015). Some of these tests are listed in Table 40-5, which is by no means all inclusive.
Overall, these eforts have resulted in testing strategies with poor sensitivity and with poor positive-predictive values for preeclampsia (Conde-Agudelo, 2015; Odibo, 2013). Currenty, no screening tests or preecampsia are predictaby reliable, vali, and economical However, combinations of tests, some yet to be adequatelyevaluated, may be promising (Gallo, 2016; Olsen, 2012).
Most tests in this category are cumbersome, time consuming, and overall inaccurate. To evaluate blood pressure changes, three tests assess the blood pressure rise in response to a stimulus. In one, women at 28 to 32 weeks' gestation rest in the left lateral decubitus position and then roll to the supine position. With this rol-over test, increased blood pressure with this maneuver signifies a positive test. he isometric exercise
TABLE 40-5. Predictive Tests for Development of the Preeclampsia Syndrome
Roll-over test, isometric handgrip or cold pressor test, pressor response to aerobic exercise, angiotensin-II infusion, midtrimester mean arterial pressure, platelet angiotensin-II binding, renin, 24-hour ambulatory blood pressure monitoring, uterine artery r fetal transcranial Doppler velocimetry
Human chorionic gonadotropin (hCG), alpha-fetoprotein (AFP), estriol, pregnancy-associated protein A (PAPP A), inhibin A, activin A, placental protein 13, procalcitonin, corticotropinreleasing hormone, A disintegrin, ADAM-12, kisspeptin