CHICKASAW COUNTY, Iowa (KCRG-TV9) -- Court records say medics and deputies were called to the couple's apartment on August 30.
Koehn called 911 to request an ambulance and said the child had died a few hours after they had fed him.
When medics and deputies arrived on the scene, they found the four-month-old dead in a swing.
Sterling weighed less than seven pounds and was 14 inches long at the time of the autopsy.
The measurements put Sterling below the 5th percentile in size and weight.
Court documents say a medical examiner found maggots in Sterling's clothing and on his skin.
The study of the maggots indicated he hadn't had a diaper change, bath or been taken out of the seat in over a week.
Investigation of the incident led to the discovery that what the parents had said was not consistent with the findings of the autopsy and investigation.
The cause of death was a failure to provide critical care.
A Chickasaw County couple is facing first-degree murder and child endangerment charges for the death of their four-month old child in August.
28-year-old Zachary Koehn and 20-year-old Cheyanne Harris are being held on $100,000 bond.
The Chickasaw County Sheriff's Office said emergency responders answered a call of an unresponsive four-month-old around 1 p.m. on August 30 at an apartment on Hilltop Avenue in Alta Vista. Upon arrival, responders found the child dead in his infant swing.
The Sheriff's Office has not released any additional information.
Online court records show both Koehn and Harris are due in court for a preliminary hearing November 2.
If convicted, they each face up to life in prison.