Volume-corrected renal arterial pulsatility index in IVF-ET fetuses and naturally conceived fetuses: establishing reference ranges and correlation with gestational age

Abstract Introduction The effect of in vitro fertilization-embryo transfer (IVF-ET) on fetal renal development remains insufficiently characterized. This study investigated the volume-corrected renal arterial pulsatility index (vcRAPI) in IVF-ET and naturally conceived fetuses, examined its correlation with gestational age, and established mid-gestational reference ranges. Methods This prospective, observational, single-center study included 286 singleton pregnancies at 22–26 weeks of gestation, including 143 IVF-ET pregnancies and 143 naturally conceived pregnancies. Bilateral fetal renal ultrasound examinations were performed to measure renal length, width, thickness, and arterial pulsatility index (PI). vcRAPI was calculated by dividing PI by the corresponding renal volume. The primary objective was to establish gestational age-specific vcRAPI reference ranges, while comparison by conception method was exploratory. The IVF-ET group was clinically heterogeneous and included pregnancies achieved through potentially different ART-related pathways, which were not further stratified in this study. Results No statistically significant differences were found in left kidney length, width, thickness, volume, PI, or vcRAPI, nor in the corresponding right kidney measurements, between the IVF-ET and naturally conceived groups (all P > 0.05). These findings indicate an absence of statistically detectable differences within this cohort rather than evidence of equivalence between conception groups. Renal parameters varied significantly across gestational ages (all P < 0.001), except for right kidney PI (H = 2.767, P > 0.05). vcRAPI showed a significant negative correlation with gestational age for both kidneys (Spearman's rho = −0.469 and −0.437, respectively; both P < 0.001). At 26 weeks, the reference range of vcRAPI was 0.369–0.837 for the left kidney and 0.326–0.798 for the right kidney. Conclusion In this single-center cohort of fetuses examined at 22–26 weeks of gestation, no statistically detectable differences in vcRAPI were observed between IVF-ET and naturally conceived fetuses. This exploratory finding should not be interpreted as evidence of equivalence, particularly because the IVF-ET group was heterogeneous and was not stratified by ART-related subtypes. vcRAPI showed a moderate negative correlation with gestational age and may serve as an exploratory research parameter for describing fetal renal Doppler-volume changes during mid-gestation. However, its clinical significance remains uncertain and requires external validation together with correlation to prenatal and postnatal outcomes before any clinical application.