Police and prosecutors said DNA testing determined the woman, now in her late 40s, was the mother of the infant, Kreiszeitung.de reported. The body was discovered in a trash can at a roadside rest area in the Rotenburg district in Lower Saxony.
The woman was convicted of manslaughter and attempted manslaughter this year and sentenced to four years. Last year, the bodies of two babies were found in an attic at her ex-husband's home in Ostertimke in Rotenburg.
Investigators said the woman gave birth secretly in 1996 and 2001 after denying her pregnancies and then hid the corpses. Under police questioning, she talked about a third pregnancy, leading to the exhumation of the baby found in 1988.
Police said the body was well-preserved, allowing DNA testing.