To establish longitudinal reference values for cerebral ventricular size in the most vulnerable patients at risk for intraventricular hemorrhage (IVH) and posthemorrhagic ventricular dilatation (PHVD).

This retrospective study included neurologically healthy preterm neonates born at 23^0/7-26^6/7 weeks of gestational age between September 2011 and April 2019. Patients were treated at 2 Austrian tertiary centers, Medical University of Vienna and Medical University of Innsbruck. All available cerebral ultrasound scans until 30 weeks corrected age were analyzed. Ventricular measurements included ventricular index, anterior horn width (AHW), and thalamo-occipital distance (TOD) and longitudinal percentiles were created.

The study cohort consisted of 244 preterm neonates, with a median gestational age of 25^3/7 weeks (IQR, 24^4/7-26^0/7 weeks) and a median birth weight of 735 g (IQR, 644-849 g). A total of 993 ultrasound scans were available for analysis, resulting in >1800 measurements of ventricular index, AHW, and TOD. Special attention was given to the 97th percentile as well as 2 mm and 4 mm above the 97th percentile, which are used internationally as cutoffs for intervention in the presence of PHVD.

We present percentile charts based on a cohort of extremely premature infants including neonates born at the border of viability suited to follow-up the most vulnerable patients at risk for IVH and PHVD. Furthermore, we provide an extensive literature research and comparison of all available reference values, focusing on ventricular index, AHW, and TOD.