There are evolutionary adaptations to the local environment of Northern Europe that Africans lack: light skin, light hair, light eyes.
There are cultural aspects such as the wearing of veils for women.
This has a significant impact on Vitamin D generation from the available sunlight.
https://sunburnmap.com/ - March 2021, a central European city will give saturation-level Vitamin D generation (before redness appears from preliminary sunburn) to a person with light features in 22 minutes, or someone with the darkest features in 1h40 minutes.
Just as Northern Europeans are evolutionarily and culturally poorly adapted to central Africa, so are Africans to Northern Europe.
But it's not true to say I'm racially inferior for Hawaii living or that I'm not suited for going on vacation. What I should've done is wear more sunscreen.
Different social strata.
Parents working in different jobs, maybe more prone to go in contact with dangerous substances or living in more contaminated areas.
Different diets, maybe relying more in very cheap food choices.
Different country, with different resources and laws that could lead this women to not be fully aware of the local opportunities available in their pregnancy, or how to ask for their rights.
Recent campaigns of hate against immigrants in Swedden, that could lead to a worse treatment in hospitals by one or a few racist members of the staff.
Not able to pay for a premium healthcare while giving birth.
And immigrants live in countries with poor environmental laws and endure a dangerous travel that can damage their health. Dangerous levels of heavy metals were found in workers that had to burn hardware and recycle computers in a third world country to pay for their travel to Europe, for example. Somali people also eat a lot of migrant fish (aka: mercury with fins).
Vitamin D is just one in a thousand of possible explanations