The Syrian migrant family's ordeal happened after they were turned back at the French border in 2014.
The woman was allegedly left bleeding at a station in Brig, without medical help, despite her husband's pleas.
The train later reached Domodossola in Italy, where she was rushed to hospital but the baby girl was already dead.
According to Italian doctors, the baby could have been saved if Swiss authorities had acted right away.
The family were on a Milan-Paris night train, but were taken off at Pontarlier, in France.
Then Swiss border guards escorted them on a long bus journey from the border to Brig train station in Switzerland, not far from the Italian border.
Reports say the 22-year-old woman's waters broke during that bus journey. Seven months pregnant, she was travelling with her husband and three small children.
The family eventually got asylum in Italy. Most Syrian migrants are entitled to asylum in Europe under international humanitarian law.
It is not yet clear what charges the guard will face. He was in charge of the border guard team at the time.
The charges depend partly on whether prosecutors can determine where the unborn child died.
The Swiss Border Guard Service says it has improved medical assistance for migrants since the 2014 incident.
A note on terminology: The BBC uses the term migrant to refer to all people on the move who have yet to complete the legal process of claiming asylum. This group includes people fleeing war-torn countries such as Syria, who are likely to be granted refugee status, as well as people who are seeking jobs and better lives, who governments are likely to rule are economic migrants.
A senior Swiss border guard faces prosecution over the failure to get medical help for a pregnant Syrian woman who later had a stillbirth.