"When we know that many people are on the move in Europe and that many out of them are not registered," he says, "this uptick in numbers I guess it was quite expected."
An undocumented person is one who has no legal right to remain in Sweden. The person could be someone who overstayed their visa, illegally entered the country or had their asylum application rejected.
Children born to undocumented parents are registered at the Swedish Tax Agency with a date and a time of birth but lack citizenship/legal residency and other identification in Sweden.
According to figures compiled by Swedish Radio News, 135 undocumented children were born in the first eight months of this year at eight hospitals nationwide, while 145 were born all of last year.
But it's difficult to get accurate figures and no one knows the exact number of how many such children there are.
"The number of children living in hiding is, of course, probably much higher. According to (the charity) Save the Children it could amount to a couple of thousand children – but actually born in Sweden, no one knows really," Malmberg says.
He adds that children without legal status in Sweden live in a "stressful situation" and there are no easy solutions to the problem, but that one would be cutting the processing time on asylum applications, since long waits can drive families underground.