Relationship between fetal middle cerebral artery pulsatility index and cerebroplacental ratio with adverse neonatal outcomes in low-risk pregnancy candidates for elective cesarean section: A cross-sectional study

Abstract Background The cerebroplacental ratio (CPR) is an important factor for predicting adverse neonatal outcomes in appropriate-for-gestational-age fetuses. Objective To evaluate whether there is an association between the CPR level and adverse neonatal outcomes in appropriate-for-gestational-age fetuses. Materials and Methods This cross-sectional study included 150 low-risk pregnant women candidates for elective cesarean sections at the gestational age of 39 wk. CPR and middle cerebral artery pulsatility index (MCA PI) were calculated in participants just before cesarian section. Postnatal complications were defined as an adverse neonatal outcome such as an Apgar score of the neonate ≤ 7 at 5 min, neonatal intensive care unit (NICU) admission, cord arterial pH ≤ 7/14, and meconium stained liquor. Results The mean age of participants was 31.53 ± 4.91 yr old. The mean CPR was reported as 1.83 ± 0.64. The Chi-square test analysis revealed that a low MCA PI and a low CPR were significantly associated with decreased cord arterial pH, decreased Apgar score at 5 min, and NICU admission (p < 0.001). There was no significant association between umbilical artery PI with arterial cord pH, Apgar score at 5 min, NICU admission, or meconium stained liquor. The Mann-Whitney test showed that a lower fetal weight appropriate for the women's gestational age was significantly associated with a decreased CPR and MCA PI (p < 0.005). There was no significant association between amniotic fluid index and CPR, umbilical artery PI, or MCA PI. Conclusion The CPR is a significant factor in predicting adverse neonatal outcomes and ultimately neonatal mortality and morbidity of low risk, appropriate-for-gestational-age fetuses.


Introduction
Adverse neonatal outcomes are among the greatest challenges for obstetrics (1). Fetal hypoxia occurs for a variety of reasons and might lead to neonatal mortality and morbidity. Numerous conditions such as maternal infections, medical disorders, preterm delivery, maternal bleeding, and fetal growth restriction can cause hypoxia and fetal distress (2)(3)(4)(5). Decreased fetal cerebral blood flow leads to activation of compensatory mechanisms by reducing the resistance of cerebral arteries to supply cerebral oxygenation (5,6). Fetal hypoxia is assessed using different tests such as the non-stress test, amniotic fluid index (AFI), biophysical profile, and fetal vascular Doppler ultrasound (2,7,8). The middle cerebral artery pulsatility index (MCA PI) and umbilical artery pulsatility index (UA PI) are used to evaluate fetal hypoxia with Doppler ultrasound. The cerebroplacental ratio (CPR) is also a significant predictor in the evaluation of hypoxia and fetal distress (8).
Due to uterine contractions during normal vaginal delivery (NVD), the blood supply to the fetal arteries might be affected, which causes the fetus to be exposed to varying degrees of hypoxia and perinatal complication (9). A study showed that a low CPR reflects fetal hypoxemia (e.g. brain sparing) in fetal growth restriction (FGR) and helps to identify adverse neonatal outcomes (10). In 2018 a study showed that a lower CPR is associated with a higher risk of intrapartum fetal distress and composite adverse perinatal outcomes (11).
Studies have been performed in recent years to investigate the relationship between fetal vascular Doppler indices and the increased risk of adverse neonatal outcomes in NVD candidates as well as in FGR cases and showed that a low MCA PI was associated with an increased risk of adverse neonatal outcomes (12)(13)(14). In the present study, the confounding factors of NVD and FGR were eliminated as only candidates for elective cesarean section (C-section) with fetal weight appropriate for gestational age (AGA) were included.
This study aimed to explore the relationship between fetal MCA PI and CPR with adverse neonatal outcomes in low-risk pregnancies, as well as the accuracy of CPR in predicting mortality and morbidity in infants.

Results
The demographic details of the participants are summarized in  Table IV shows that there was no significant association between AFI and CPR, UA PI, or MCA PI.   Table III. Association between fetal weight in appropriate for gestational age with cerebroplacental ratio, umbilical artery pulsatility index and middle cerebral artery pulsatility index  Numerous studies have shown that a low CPR indicates redistribution of fetal blood flow according to the brain-sparing hypothesis and predicts adverse neonatal outcomes (17)(18)(19). Some studies have shown that CPR is a major independent predictor of stillbirth and perinatal morbidity. Even in low-risk pregnancies candidates for NVD, a low CPR increases the risk of C-section (20)(21)(22).
In 2015, a study showed that CPR had a high sensitivity in the prediction of fetal heart rate abnormalities and adverse neonatal outcomes in low-risk pregnancies at 40 wk and beyond (23).
Also, in 2020 a study showed that a lower CPR in AGA fetuses was associated with a higher risk of C-section and adverse neonatal outcomes which is similar to the results of our study. Our study differed in that we had a larger sample size and eliminated the NVD confounding variable (24).
Another study conducted in 2021 found that a lower CPR in AGA fetuses at 37-40 wk of gestation was associated with a higher risk of C-section and adverse neonatal outcomes (25). Therefore, a low CPR in AGA fetuses can be a sign of hypoxia and adverse neonatal outcomes, although further studies are needed to confirm this (26).
The strength of this prospective study lies in its design which minimized the impact of any A low CPR in AGA fetuses was associated with an increased risk of adverse neonatal outcomes, a lower neonatal cord arterial pH and Apgar score, and a higher risk of NICU admission. Therefore, based on these findings, it is recommended that CPR is checked in women candidates for elective C-section at 38 wk of gestation. If the CPR is < 5%, a C-section at 38 wk of gestation may be helpful in the presence of a neonatologist to prevent adverse neonatal outcomes. However, more research is needed with a larger sample size to conclude whether earlier termination of pregnancy would be cost-effective and safe in these cases.

Conclusion
CPR is a non-invasive important factor in predicting adverse neonatal outcomes and ultimately neonatal mortality and morbidity. Even in AGA fetuses, a low CPR can predict adverse neonatal outcomes.