"Avance" is not the full report; it refers to information given in advance of the full report (which may take some time, while a range of analyses are performed). It usually means the cause of death, which is the first thing the post-mortem examination seeks to establish, and the identity of the deceased, if that was not already clear.

For a UK audience you could use either post-mortem or autopsy, but the former is more common in official UK documents, as opposed to press reports.

I think "findings" could be used as an alternative to "results". I'd be inclined not to use "report" here, because an "avance" may be communicated verbally, before it's been written up as a report.

"El avance de autopsia apunta que los cadáveres pertenecen a la madre e hija desaparecidas en Sevilla y a su pareja [...]"
https://www.europapress.es/andalucia/sevilla-00357/noticia-a...

In this case there's no mention yet of cause of death; the state of the bodies made that difficult to determine and they'll have to do more work to establish it. This "avance" just establishes identity.

"El pequeño Julen falleció de un traumatismo cranoencefálico. [...] Así de clara es la primera conclusión del informe preliminar de la autopsia al que ha tenido acceso 'Espejo Público'. [...]
Destacable es que con este avance de autopsia no es posible descartar que la piqueta, de siete kilos de peso y un metro de largo, pudiera llegar al cuerpo del niño. De hecho, establece que Julen presentaba varias heridas 'post morten'."
https://www.antena3.com/programas/espejo-publico/noticias/au...