Elizabeth Whitehead was on her way to the hospital for what she believed was a stomach ailment when she unexpectedly delivered a 2-and-a-half-pound baby boy in her front yard.

The 21-year-old woman, who didn’t know she was pregnant, gave birth outside her New Jersey home in Barnegat Township on Tuesday. "It all happened on the grass," Whitehead told Patch. "His head was out when I was on the grass."

Whitehead’s boyfriend, David Windham, called 911. Barnegat Township Police officers Vinnie Damiano and Michael Moore said the infant appeared to be three-months premature and wasn’t breathing. The officers performed CPR on the newborn and resuscitated him before being transported to a hospital, NBC 10 reports.

"Once I heard a little bit of the cry, it kind of made me jump a little bit," Moore said.

Before the unexpected arrival, the young couple were already parents to a 9-month-old boy. Whitehead said she took two pregnancy tests after she stopped getting her period. They both came back negative, Patch reports.

Whitehead thought she was getting her period when she experienced abdominal cramps on Tuesday. Soon they got worse, so she decided to head to the hospital but gave birth before she could.

The newborn was 24 weeks old at birth -- about four months premature. So far, "the baby is fine," Windham said.

The newborn was first transported to Southern Ocean Medical Center in Manahawkin and later transferred to Jersey Shore University Medical Center in Neptune, according to the Asbury Park Press. Whitehead was treated at Southern Ocean Medical Center, where she was later released, police said.

Neighbors remain shocked by the news, adding Whitehead didn’t look pregnant. "Can't say that I noticed that she was pregnant," Pat Farald, a neighbor, told NBC Philedelphia. "She carries well."