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 .
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The cerebroplacental ratio (CPR) is emerging as an important predictor of adverse pregnancy outcome, and this has implications for the assessment of well-being in fetuses diagnosed as small for gestational age (SGA) and those appropriate for gestational age (AGA) close to term. The CPR is calculated by dividing the Doppler indices of the middle cerebral artery (MCA) by the umbilical artery (UA) ( Table 1 and Figure 1 ).
| Study | Year | Study type | Doppler indices | Computation of ratio | Abnormal criteria |
|---|---|---|---|---|---|
| Arbeille et al | 1988 | Cross-sectional | S-D/S | MCA/UA | Ratio <1 |
| Arias | 1994 | Cross-sectional | RI | MCA/UA | Ratio <1 |
| Gramellini et al | 1992 | Cross-sectional | PI | MCA/UA | Ratio <1.08 |
| Bahado-Singh et al | 1999 | Cross-sectional | PI | MCA/UA MoM | Ratio <0.05 MoM |
| Baschat and Gembruch | 2003 | Cross-sectional | PI | MCA/UA | Less than fifth centile |
| Odibo et al | 2005 | Cross-sectional | PI | MCA/UA | Ratio <1.08 |
| Ebbing et al | 2007 | Longitudinal | PI | MCA/UA | <2.5th centile |
| Morales et al | 2014 | Cross-sectional | PI | MCA/UA | Less than fifth centile or MoM <0.6765 |
The CPR represents the interaction of alterations in blood flow to the brain as manifest by increased diastolic flow as the result of cerebrovascular dilation resulting from hypoxia and increased placental resistance, resulting in decreased diastolic flow of the umbilical artery. When these alterations occur, the increased diastolic flow of the MCA is manifest by a decrease in the systolic/diastolic ratio (S/D), resistance index (RI); [(systolic peak velocity/diastolic peak velocity)/systolic peak velocity], and the pulsatility index (PI); [(systolic peak velocity/diastolic peak velocity)/velocity time integral], whereas these measurements are increased in the umbilical artery as the result of increased resistance to blood flow as the result of placental pathology. Although the S/D ratio, RI, and PI have been reported when computing the CPR, more recently the PI is the computation of choice.
An abnormal CPR may result from 3 types of Doppler measurement patterns. The first is when the UA and MCA PI are in the upper and lower range of the distribution curve, resulting in an abnormally low CPR ( Figure 2 ). The second is when the UA PI is normal but the MCA PI is decreased, resulting in an abnormally low CPR ( Figure 3 ). The third pattern consists of an abnormally elevated UA PI and an abnormally decreased MCA PI, resulting in an abnormally low CPR ( Figure 4 ).
Whereas the CPR was first described in the 1980s, interest in this assessment tool has been rekindled because of recent reports associating an abnormal ratio with adverse perinatal outcome and postnatal neurological deficit. The purpose of this article was to review the data from studies in which the CPR has been evaluated in fetuses that were AGA and those with SGA to determine whether this test should be considered for integration into clinical practice.
Appropriate-for-gestational-age fetuses: the role of CPR in the detection of fetuses at risk for adverse outcome
Prior et al prospectively evaluated 400 AGA fetuses at term and reported an abnormal CPR in 11%. Of those who underwent cesarean delivery for fetal distress, 36.4% had an abnormal CPR compared with 10.1% ( P < .001) that had a normal CPR ( Table 2 ). An abnormal CPR was a better predictor for an emergency cesarean delivery than an abnormal UA or MCA ( Table 2 ). No fetuses with a CPR greater than the 90th centile required cesarean delivery for fetal distress in labor. Therefore, the assessment of the CPR in term AGA fetuses before active labor predicted intrapartum fetal compromise and the need for emergency cesarean delivery.
| Variable | Cruz-Martinez et al (2011) | Prior et al (2013) | Figueras et al (2014) | Morales-Rosello et al (2015) | Khalil et al (2015) | Khalil et al (Part I) (2015) |
|---|---|---|---|---|---|---|
| Type of study | Prospective | Prospective | Prospective | Retrospective | Retrospective | Retrospective |
| Purpose of study | Evaluate CPR to predict emergency cesarean delivery for fetal distress in term fetuses with late-onset SGA | Evaluate CPR obtained before labor to detect fetuses at risk for emergency cesarean delivery for fetal distress | Develop an integrated model to predict adverse outcome in fetuses with late-onset SGA | Determine whether SGA and appropriate-for-gestational-age term fetuses with a CPR have worse neonatal acid–base status than those with a normal CPR | Compare CPR and EFW at term to detect NICU admission when CPR obtained during midthird trimester | Evaluate CPR and birthweight models in term fetuses to predict operative delivery for fetal compromise and admission to the NICU |
| Gestational weeks ultrasound studies were obtained | >37 | 37–42 | 34–40 | 37–41.9 | 34 +0 to 35 +6 | >37 |
| Classification and number of fetuses studied, n, % | Control (n = 210), suspected SGA (n = 210) | Low-risk patients (n = 400) | No control SGA (n = 509) | All patients (n = 2927), SGA (n = 640, 25.8%) | All patients (n = 2485) SGA (n = 640, 25.8%) | All patients (n = 8382) SGA (n = 1282, 15.3%) |
| Interval from ultrasound to delivery | Induction after 37 wks | Examined within 72 h of delivery | Not stated | Up to 2 wks | Up to 6 wks | 2 wks |
| Type of CPR measurement (abnormal Value) | PI less than fifth centile | PI <10th centile (<1.24) | PI (<10th centile) | PI MoM <0.6765 | PI MoM <0.6765 | PI MoM <0.6765 |
| Did CPR perform better than other tests? | Yes (MCA) | Yes (UA, MCA) | No (CPR combined with UtA PI >95th centile and EFW less than third centile) | Yes (birthweight) | Yes (EFW, birthweight centile) | Yes (birthweight centile) |
| Findings at birth: classification by abnormal vs normal CPR | ||||||
| Weeks of gestation at delivery | — | 40 +5 vs 40 +3 ( P < .004) | 38.1 vs 38.5 (not significant) | — | — | — |
| Mean birthweight, g | — | Not significant | 2280 vs 2466 ( P < .001) | — | — | — |
| Birthweight centile, n,% | — | 48 vs 55 ( P = .04) | — | — | — | — |
| Abnormal fetal heart rate monitoring during labor | — | 86% vs 31% ( P < .001) | — | — | — | — |
| Operative delivery for fetal distress (cesarean delivery, instrumental delivery) | CPR less than fifth: 37.8% (14/37) CPR more than fifth: 20.4% (29/142) ( P < .001) | 36.4% vs 10.1% ( P < .001) | 79.1% vs 10.7% ( P < .001) | — | — | 13.1% vs 9.4% ( P < .01) |
| Neonatal findings: classification by abnormal vs normal CPR | ||||||
| Meconium stained liquor | — | 22.7% vs 9% ( P = .02) | — | — | — | |
| Apgar <7 at 5 minutes | — | Not significant | 0.7% vs 1.3% (not significant) | — | — | — |
| Abnormal cord pH | — | Not significant | UA 7.17 vs 7.25 ( P < .001) | UA and UV | — | — |
| Newborn intensive care unit admission | — | Not significant | All patients 12.6% vs 6.1% ( P < .001) SGA 22.5% vs 8.4% ( P < .001) AGA 9.8% vs 5.5% Not significant | 14.3% vs 9.7% ( P = .004) | ||
| Neonatal complications | — | Not significant | 11.25% vs 5.6% ( P = .03) | — | — | — |
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