Third Trimester Umbilical Artery Doppler in Low-Risk Pregnancies and its Correlation to Estimated Fetal Weight and Birthweight

Abstract

Purpose This study investigated the correlation between the umbilical artery (UA) pulsatility index (PI) and the estimated fetal weight percentile and birthweight (BW) percentile, respectively.

Materials and Methods We included low-risk pregnancies, in which UA Doppler investigations after 28 weeks were performed. Cases were allocated according to BW percentiles: small for gestational age (SGA) with BW < 10^th percentile; appropriate for gestational age (AGA) and large for gestational age (LGA) with BW > 90^th percentile. We analyzed differences in the mean UA-PI and UA-PI z-score for gestational age according to the three groups. Linear regression was performed to evaluate any relationship between Doppler indices and BW percentiles. Multiple logistic regression analysis was performed to determine the independent association of UA-PI with LGA babies. In a second step, we considered data on estimated fetal weight (EFW) percentiles and performed the same analysis.

Results We analyzed 14 554 pregnancies from 2004 to 2015. The mean UA-PI and mean UA-PI z-scores in the LGA group were lower than in the AGA and SGA groups (p < 0.001). UA-PI and UA-PI z-scores were linearly related to birthweight percentiles (p < 0.001) and to EFW percentiles (p < 0.001). Logistic regression analysis showed that low UA-PI was independently associated with neonatal LGA (p < 0.001).

Conclusion The higher the EFW and BW percentiles, the lower the UA-PI. However, reference ranges for UA Doppler are only based on gestation weeks. Further studies are needed to clarify whether customized reference ranges based on EFW percentiles are more appropriate for the evaluation of fetal wellbeing in the third trimester.

Zusammenfassung

Ziel Diese Studie untersuchte den Zusammenhang zwischen dem Pulsatilitätsindex (PI) der Nabelarterie (UA) und den geschätzten Perzentilen des Fetalgewichts sowie des Geburtsgewichts (BW).

Materialen und Methoden Aufgenommen wurden Low-Risk-Schwangerschaften nach der 28. Schwangerschaftswoche, bei denen UA-Doppleruntersuchungen durchgeführt wurden. Die Fälle wurden nach den BW-Perzentilen wie folgt eingeteilt: zu klein („small for gestational age“, SGA) mit BW < 10. Perzentile; entsprechend („appropriate“, AGA) und zu groß für das Gestationsalter („large“, LGA) mit BW > 90. Perzentile. Wir analysierten die Unterschiede im mittleren UA-PI und UA-PI-Z-Score nach dem Schwangerschaftsalter entsprechend den 3 Gruppen. Eine lineare Regression wurde durchgeführt, um jegliche Relation zwischen Doppler-Indizes und BW-Perzentilen zu bewerten. Multiple logistische Regressionsanalysen wurden durchgeführt, um den unabhängigen Zusammenhang des UA-PI mit LGA-Kindern zu bestimmen. In einem zweiten Schritt führten wir die gleiche Analyse im Hinblick auf die geschätzten Fetalgewicht (EFW)-Perzentilen durch.

Ergebnisse Von 2004 bis 2015 analysierten wir 14 554 Schwangerschaften. Der mittlere UA-PI und der mittlere UA-PI-Z-Score in der LGA-Gruppe waren niedriger als in der AGA- und SGA-Gruppe (p < 0,001). Der UA-PI und die UA-PI-Z-Scores standen in linearem Zusammenhang mit den BW-Perzentilen (p < 0,001) und den EFW-Perzentilen (p < 0,001). Die logistische Regressionsanalyse zeigte, dass ein niedriger UA-PI unabhängig mit LGA des Neugeborenen assoziiert war (p < 0,001).

Schlussfolgerung Je höher die EFW- und BW-Perzentilen, desto niedriger der UA-PI. Die Referenzbereiche für den UA-Doppler basieren jedoch nur auf Schwangerschaftswochen. Weitere Studien sind erforderlich um zu klären, ob angepasste Referenzbereiche auf Basis von EFW-Perzentilen für die Beurteilung des fetalen Wohlbefindens im dritten Trimenon besser geeignet sind.

Key words

obstetrics - doppler - umbilical artery - fetal weight - macrosomia

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