Fetal growth restriction (FGR) still remains one of the most difficult conundrums in fetal medicine. Umbilical artery Doppler indices also had limited role in predicting perinatal outcome, in fetuses with subtle reduction in growth and liquor.
It is well-known that cases of mild FGR are also associated with poor perinatal outcome and are missed more often than the cases with severe FGR especially in countries like India, where most of the obstetricians in the rural areas still use only clinical examination in assessing the fetal growth.
A prospective observational study was conducted by Paladugu S, Mundkur A, Yedlapalli S, et al correlating perinatal outcomes with renal artery and umbilical artery Doppler indices and analyzing their sensitivities and specificities between August 2016 and May 2018 was published in International Journal of Infertility and Fetal Medicine.
Women with multifetal pregnancy, fetal anomalies/fetal renal anomalies, who had preterm deliveries before 34 weeks and with early-onset FGR at the time of first scan (28–31 weeks) were excluded.
The growth parameters, amniotic fluid index, umbilical artery Doppler, and renal artery Doppler at two different gestations, 28–31 weeks and 32–34 weeks, were evaluated.
The cutoffs established for PI (Pulsatility index) and RI (resistivity index) at 28–31 weeks were 2.8 and 0.91. The PI at 32–34 weeks could predict FGR. But the RI at 32–34 weeks could not predict FGR and the area under the receiver operating curve (ROC) curve was just above 0.5, hence cut-off with good sensitivity and specificity could not be established. Mean umbilical artery PI in both the groups was normal even in FGR cases.
The optimal cutoffs established for PI were 3.07 and 2.2 at 28–31 weeks and 32–34 weeks, respectively, analyzed using the ROC.
Pulsatility indices of renal artery Doppler evaluated at both gestational ages could predict oligohydramnios, with higher values indicating high risk.
Renal artery Doppler at 28–31 weeks was able to predict spontaneous preterm birth with good sensitivity and specificity, above the cutoff of 2.8 PI and 0.97 RI.
The mean PI and RI of renal artery Doppler at 32–34 weeks were 2.2 ± 0.28 and 0.85 ± 0.10. Among the preterm deliveries analyzed, the mean PI was statistically significant for preterm deliveries with p value of 0.04. The sensitivity and specificity were 56.62 and 71.6%.
The renal artery Doppler PI and RI at 28–31 weeks of normal fetuses when compared with babies who had NICU admissions showed they were statistically significant in predicting the outcome with good sensitivity and specificity of 88 and 73% for PI. The RI was not found to be statistically significant.
Overall, it was observed that the mean umbilical artery PI and RI were within normal ranges in all cases, irrespective of normal birth weight, FGR, oligamnios, preterm birth, or low birth weight.
In the present study, there was also a significant correlation between spontaneous preterm deliveries and renal artery Doppler indices. There was an increase in blood flow to kidney compared to the other fetuses.
In the 394 patients studied, 13.1% were having FGR, 12.2% were oligoamnios, and 12.2% had preterm delivery. The p values of the pulsatility index and the resistivity index of the renal artery in FGR, oligoamnios, preterm delivery, and low birth weight were more significant than umbilical artery Doppler indices.
The study concluded, "Renal artery Doppler indices were significantly more reliable in predicting adverse perinatal outcomes than umbilical artery Doppler indices. Additionally, renal artery Doppler indices were able to pick up these changes earlier, hence can be a potential early indicator, and PI being more specific and sensitive.
In this study, a newer marker has been identified in significant cases with mild presentation of uteroplacental insufficiency. Hence, further research into fetal renal artery Doppler with a larger population and larger studies involving cases and controls is required."
Limitations of study: Renal volume, parenchymal thickness, and peak systolic velocities were not studied in the present study. A larger study with randomization involving both high risk and low risk would improve both the quality and quantity of data.
Source: : Paladugu S, Mundkur A, Yedlapalli S, et al. Performance of Fetal Renal Artery Doppler Compared with Umbilical Artery Doppler in Mild and Moderate Fetal Growth Restriction: An Observational Study in a Tertiary Care Hospital. Int J Infertil Fetal Med 2020;11(1):1–4.