Association between third trimester cerebro-placental ratio and adverse outcomes in appropriate for gestational age foetuses
Date of Award
Master of Medicine (MMed)
Dr. Sikolia Wanyonyi
Dr. Steve Mutiso
Obstetrics and Gynaecology (East Africa)
Background: Small for gestational age (SGA) fetuses are at increased risk of adverse outcomes and appropriate vigilance is put in place in terms of antenatal and intrapartum surveillance. Appropriate for gestational age (AGA) fetuses have a lower incidence of adverse outcomes, although majority of these outcomes occur in this cohort. AGA fetuses can fail to reach their genetic growth potential due to placental insufficiency and 25 % have actually been found to have placental histological features of chronic hypoxia. Therefore, there is need to use other methods of screening for adverse perinatal outcomes apart from estimated fetal weight (EFW), with focus being directed toward detecting those that are hypoxic and not just small. We undertook to determine the association between third trimester cerebro-placental ratio (CPR) and adverse perinatal outcomes and utility of CPR in predicting the same in AGA fetuses.
Methodology: This was a retrospective cohort study. Secondary analysis of data from the ‘Routine third trimester obstetric ultrasound for detection of small for gestational age and growth restricted fetus in low risk pregnancy- a non-inferiority randomized control trial ‘(ROTTUS trial) was done. The 150 participants in ROTTUS Trial who had obstetric ultrasound scans done between 35 to 38+6 weeks, had AGA fetuses and Middle cerebral artery (MCA) and Umbilical artery (UA) Pulsatility index (PI) recorded were included. CPR was derived as a ratio of MCA PI to UA PI and categorized as normal (≥ 10th centile) or abnormal (< 10th centile). Association of CPR with composite adverse perinatal outcomes (CAPO) (defined as APGAR Score <7 at 5 minutes or UA pH < 7.1 or admission to NICU or birth weight < 10th centile or still birth) was done using Chi-square tests. Logistic regression analysis was done to control for potential confounding variables. Statistical significance was interpreted at P < 0.05. Sensitivity, specificity, predictive values and positive likelihood ratios were computed for CPR < 10th centile in predicting composite adverse perinatal outcomes.
Results: A total of 21 AGA fetuses with abnormal CPR were compared to 129 fetuses who had normal CPR. The cumulative rate of CAPO was 10%, 15 cases total. There were 12 cases of SGA newborns and three cases of UA pH < 7.1. No stillbirth, APGAR score < 7 at 5 minutes or NICU admission occurred. Mean gestational at ultrasound was 36 weeks, and mean ultrasound to delivery duration was 4 weeks. 63 % (95) of women had spontaneous vaginal delivery, 19 % (28 cases) and 17 % (26 cases) had elective and emergency caesarean sections respectively, with 1 having vacuum delivery. There was no difference between the CPR groups in CAPO, maternal demographics, gestation at delivery, and mode of delivery. CPR performed poorly as a predictor of CAPO with aOR 1.08 (95% C.I: 0.25,7.43), with a sensitivity of 13%, Positive predictive value of 10%, specificity of 86%, Negative predictive value of 90% and positive likelihood ratio of 0.95.
Conclusion: There is no association between abnormal CPR and CAPO in AGA fetuses. CPR is a poor predictor of CAPO in this cohort of fetuses. CPR as part of routine third trimester ultrasound assessment in appropriately grown fetuses of low risk pregnancies is not recommended for the purpose of prediction of adverse outcomes.
Kimani, M. W. (2022). Association between third trimester cerebro-placental ratio and adverse outcomes in appropriate for gestational age foetuses (Unpublished master's dissertation). Aga Khan University, East Africa.