## 4 Discussion
The present study indicates that bilateral hearing loss is more prevalent than unilateral hearing loss in newborns. Nevertheless, there is a considerable number of newborns with unilateral hearing loss. In the Netherlands, family-centered early intervention is only provided to children with a permanent bilateral hearing loss of \(\geq\)40 dB. However, research shows that children with unilateral hearing loss are also at risk for difficulties in their speech and language development and social-emotional development [27; 28]. The Joint Committee on Infant Hearing, therefore, recommends early intervention for children with hearing loss as well [9]. The current data reveal that there is a substantial group of children with unilateral hearing loss in the Netherlands who might benefit from family-centered early intervention. In the literature, only a few studies reported on the prevalence of hearing loss by severity [24; 25; 29; 30]. In line with these previous studies, the current findings showed that moderate hearing loss was more prevalent than severe and profound hearing loss. Within the group of children with hearing loss, a moderate hearing loss was even more prevalent than severe and profound hearing loss put together. Despite this, research on children with moderate hearing loss has been less frequent in comparison to severe and profound hearing losses [31]. Fortunately, in the last years, more research has been conducted on children with moderate hearing loss [32; 33; 34], which contributes to our knowledge on the development of this group of children and the interventions needed. While many newborn hearing screening programs worldwide are dealing with high percentages of lost to follow-up during screening and diagnostic testing [22; 23], follow-up rates within the Dutch well-baby program are high. Participation is 99.5%-99.8% per screening round, and diagnostic results were lacking for only 5.4% of the children. Even among these, most children did visit the speech and hearing center, but data on their diagnosis were missing, or parents did not provide permission to share the results. For only 50 children (1.8%), it is known that they were truly lost to follow-up. This indicates that the current prevalence data approximate the true prevalence of permanent hearing loss in newborns. Still, as the aim of the screening program is to identify all children with hearing loss, it remains important to obtain insight into the reasons why parents do not visit the speech and hearing center for diagnostic testing of their child. In order to provide children with hearing loss with the best developmental opportunities, it is important to diagnose them timely (before the age of 3 months), so intervention can start early. Of all children with permanent bilateral hearing loss in the current study, 86.9% received their diagnosis timely. The current findings indicate that completion of the diagnosis for children with a moderate hearing loss is slightly delayed compared to more severe hearing losses. This is in line with the results of a previous study on the Dutch newborn hearing screening population from 2014 [35]. According to [PERSON] and [PERSON] [35], a conductive component within the hearing loss is one of the main reasons for a delay in diagnosing a permanent hearing loss. Future research could examine the reasons for a delay in diagnosing hearing loss in a larger population. Furthermore, it would be interesting to investigate the start of intervention for the current study population. That would provide us with more insight about meeting the 1-3-6 goal in the Netherlands. A limitation of the current study is that only data from the well-baby population were used to report on the severity of the hearing loss. While these data were combined with results from children screened in the NICU to calculate Dutch national prevalence rates of uni- and bilateral hearing loss of at least 40 dB, the information on the severity of hearing loss in the NICU population was not available.