Is Preeclampsia More Than One Disease?

Some believe that key characteristics of preeclampsia, gestational hypertension and proteinuria, represent pathogenetically distinct conditions. When fetal growth is restricted, preeclampsia could result from abnormal implantation. An infant with appropriate or high birth weight could signify a range of conditions from mild preeclampsia with modest placental involvement to a hypertensive disorder without placental disease. The investigators obtained information on gestational length and preeclampsia from 1,679,205 singleton infants born in the years 1967 to 1978 and entered it in a population-based registry. Preeclampsia was diagnosed in 44,220 pregnancies, 2.6% of the total. Criteria included a rise in blood pressure to at least 140/90 mm Hg after 20 weeks gestation, with a diastolic pressure at least 15 mm Hg higher than before week 20 or a systolic pressure at least 30 mm Hg higher. Proteinuria of at least 0.3 g/24 hours also had to be present. If the infant weighed less than 2 standard deviations (SDs) below the mean, the relative risk (RR) of preeclampsia was 5.9. If birth weight was 3 or more SDs above the mean, the RR was 2.4. When delivery was at term (37–42 weeks), the RR of preeclampsia was 4.5 when birth weight was less than 2 SDs below the mean and 2.6 with a birth weight 3 or more SDs above the mean. For preterm preeclampsia, the risk increased with declining birth weight. Gestational diabetes was approximately 3 times more prevalent in preterm than in term preeclampsia. These findings support the view that preeclampsia includes pathogenetically separate conditions rather than 1 basic process with varying degrees of severity. Placental dysfunction probably underlies preeclampsia associated with low birth weight, preterm delivery, and gestational diabetes. In contrast, placental function is normal when preeclampsia develops at term and the infant appears to be unaffected.