Pregnancy hypertension, placental evidences of low uteroplacental blood flow, and spontaneous premature delivery.

This study was undertaken to determine if preeclampsia and low uteroplacental blood flow cause spontaneous preterm births. No non-invasive methods are currently available to accurately measure uteroplacental blood flow, so surrogates that are known to be associated with low uteroplacental flow were used. These are preeclampsia, placental infarcts, abnormally small placental villi, and excessive syncytial knots. Preeclampsia was associated with a frequency of spontaneous preterm births that was 41% greater than expected (P less than .001). Normotensive gestations with placental findings of low uteroplacental blood flow ended preterm 147% more frequently than expected, and when a woman had two such pregnancies in succession, the second had a particularly high frequency of spontaneous preterm delivery (64%). Overall, preeclampsia and placental findings of low uteroplacental blood flow were associated with 26% of the spontaneous preterm deliveries in this study. Preeclampsia and low uteroplacental blood flow may be major causes of preterm birth.