Regardless of its cause, any chronic hypertensive disorder predisposes a woman to develop superimposed preeclampsia syndrome. Chronic underlying hypertension is diagnosed in women with documented blood pressures > 140/90 mm Hg before pregnancy or before 20 weeks' gestation, or both. Hypertensive disorders can create diicult problems with diagnosis and management in women who are not irst seen until after midpregnancy. This is because blood pressure normally drops during the second and early third trimesters in both normotensive and chronically hypertensive women (see Fig. 40-1). Thus, a woman with previously undiagnosed chronic vascular disease who is seen before 20 weeks frequently has blood pressures within normal range. During the third trimester, however, as blood pressures return to their originally hypertensive levels, it may be diicult to determine whether hypertension is chronic or induced by pregnancy. Even a careful search for evidence of preexisting end-organ damage may be futile, as many ofthese women have mild disease and no evidence ofventricular hypertrophy, retinal vascular changes, or renal dysfunction.
In some with chronic hypertension, blood pressure rises to obviously abnormal levels, typically after 24 weeks' gestation. If new-onset or worsening baseline hypertension is accompanied by new-onset proteinuria or other indings listed in Table 40-1, then superimposed preeclampsia is diagnosed. Compared with "pure" preeclampsia, superimposed preeclampsia commonly develops earlier in pregnancy. It also tends to be more severe and more often is accompanied by fetal-growth restriction. he same criteria shown in Table 40-2 are also used to further characterize severity of superimposed preeclampsia.
Young and nulliparous women are particularly vulnerable to developing preeclampsia, whereas older women are at greater risk for chronic hypertension with superimposed preeclampsia. he incidence is markedly inluenced by race and ethnicity-and thus by genetic predisposition. In one study by the Maternal-Fetal Medicine Units (MFMU) Network, the incidence of preeclampsia was 5 percent in white, 9 percent in Hispanic, and 11 percent in African-American women (Myatt, 2012a,b). In addition, black women have greater morbidity (Shahul, 2015). In several worldwide studies reviewed by Staf and coworkers (2015), the incidence of preeclampsia in nulliparous populations ranged from 3 to 10 percent. he incidence of preeclampsia in multiparas also varies and ranges from 1.4 to 4 percent (Fisher, 2015).
Bartsch and associates (2016) extracted data from more than 25 million pregnancies and calculated relative risks for several clinical factors shown in Table 40-3. Others include the metabolic syndrome and hyperhomocysteinemia (Karumanchi, 2016a; Masoudian, 2016; Scholten, 2013). Pregnancies with a male fetus are also at slightly higher risk a askolka,
TABLE 40-3. Selected Clinical Risk Factors for Preeclampsia
APA = antiphospholipid antibody; ART = assisted reproductive technology; BMI = body mass index; CHTN = chronic hypertension; CKD = chronic kidney disease; SLE = systemic lupus erythematosus.
Data from Ba rtsch, 201 6.
2017). Although smoking during pregnancy causes various adverse pregnancy outcomes, ironically, it carries a reduced risk for hypertension during pregnancy (Bainbridge, 2005; Kraus, 2014). Other factors are human immunodeficiency virus (HIV) seropositivity and sleep-disordered breathing (Facco, 2017; Sansone, 2016).