The importance of the cerebroplacental ratio in the evaluation of fetal well-being in SGA and AGA fetuses

The cerebroplacental ratio (CPR) is emerging as an important predictor of adverse pregnancy outcome, and this has implications for the assessment of fetal well-being in fetuses diagnosed as small for gestational age (SGA) and those appropriate for gestational age close to term. Interest in this assessment tool has been rekindled because of recent reports associating an abnormal ratio with adverse perinatal events and associated postnatal neurological outcome. Fetuses with an abnormal CPR that are appropriate for gestational age or have late-onset SGA (>34 weeks of gestation) have a higher incidence of fetal distress in labor requiring emergency cesarean delivery, a lower cord pH, and an increased admission rate to the newborn intensive care unit when compared with fetuses with a normal CPR. Fetuses with early-onset SGA (<34 weeks of gestation) with an abnormal CPR have a higher incidence of the following when compared with fetuses with a normal CPR: (1) lower gestational age at birth, (2) lower mean birthweight, (3) lower birthweight centile, (4) birthweight less than the 10th centile, (5) higher rate of cesarean delivery for fetal distress in labor, (6) higher rate of Apgar scores less than 7 at 5 minutes, (7) an increased rate of neonatal acidosis, (8) an increased rate of newborn intensive care unit admissions, (9) higher rate of adverse neonatal outcome, and (10) a greater incidence of perinatal death. The CPR is also an earlier predictor of adverse outcome than the biophysical profile, umbilical artery, or middle cerebral artery. In conclusion, the CPR should be considered as an assessment tool in fetuses undergoing third-trimester ultrasound examination, irrespective of the findings of the individual umbilical artery and middle cerebral artery measurements. A CPR calculator is available at http://www.ajog.org/pb/assets/raw/Health%20Advance/journals/ymob/CPR/index.htm.