Placental insufficiency among high-risk pregnancies with a normal umbilical artery resistance index after 32weeks

To determine the incidence of abnormal multi-vessel Doppler values among advanced pregnancies at risk of suboptimal placentation but with a normal umbilical artery resistance index (RI), and to assess whether clinical and ultrasonography findings can identify them.

In a prospective cross-sectional study at Tygerberg Hospital, South Africa, women with high-risk pregnancies but normal umbilical artery RI after 32weeks underwent ultrasonography (fetal biometry, liquor, and placenta maturation) and Doppler assessment (uterine, umbilical, and middle cerebral arteries) between February 11 and October 21, 2013. Study data were compared among four groups: fetuses with normal uterofetoplacental Doppler values and those with any abnormal pulsatility index, each subdivided into small for gestational age (SGA) and appropriate for gestational age (AGA) by estimated fetal weight.

Of 210 participants, 72 (36.2%) had abnormal Doppler results, and 60 (28.6%) fetuses were SGA (38 [63.3%] with abnormal Doppler results). Clinical characteristics did not differ between groups with normal or abnormal Doppler values; however, among normal Doppler results, SGA pregnancies demonstrated poorer fundal growth (P=0.006). Significant associations existed between abnormal Doppler results and asymmetric growth, inappropriately advanced placental maturation, and reduced liquor volume (all P≤0.04), but with very low sensitivities (3.9%, 4.8%, and 14.5%, respectively).

Maternal characteristics and imaging variables did not reliably identify more than one-third of pregnancies with evidence of suboptimal placentation.