This term literally means "brain damage
of unknown etiology from the birth trauma" or "general
weakness of the CNS due to birth trauma". This is, indeed,
a "catch-all" broad term often used in Russian medical
documents. It aims to indicate a child "at risk" in general:
very often no specific concern is expressed. This diagnosis is given
almost automatically to all premature babies and babies with low
Apgar scores. It refers to a risk factor (or factors) that may predict
a neurological impairment rather than real (objectively found by
medical means) neurologic damage. You should be reasonably concerned,
but remember that this diagnosis is almost a "standard"
feature of children from orphanages. Perinatal impairment of the
CNS means the same as "prenatal encephalopathy".