With her son Ryder Scott Dunlap, she was only pregnant for 27 weeks.
"He weighed one pound and nine ounces. He was 13 inches long, perfect in my eyes. He did live for one hour and sixteen minutes," Hart tearfully recalls.
She still cries when she thinks about that day.
She cries when she tells friends, and when she's alone.
"I know it'll always be that way," she said.
Doctors allowed Hart to be with her son while he was still alive. Her family was there too, which was big.
"To get to spend time with him alive meant a lot of to me," she said. "And it still means a lot to me."
Sara had just begun nursing school, when she found out she was pregnant.
A few months in, when she was getting the sonogram, doctors told her everything didn't look right.
She was transferred to St. Luke's. Then to Children's Mercy.
Then she got the news that changed everything.
"They confirmed that he had anencephaly, which is a neural tube defect," Hart recalls, her tears still welling in her eyes. "It happens within the first 28 days of being pregnant. So weeks and weeks before I even knew I was pregnant, this happened."
After telling the whole story, Sara opens a box full of memories.
She still has the knit cap her wore that morning, small enough to fit a doll; she says it was too big.
Then she pulls out the blanket she wrapped him in; it's tiny, but it covered him completely.
Sara's daughter Lexi Rae Dunlap, who is now nearly four years old, was still just a toddler herself when her baby brother was born.
Lexi still talks about her brother to anyone who asks.
"One of my all time favorite pictures is of him holding my finger," Hart said. "[Lexi] has that in her room."
This mother's ordeal is not uncommon.
In Missouri this year, 11.7% of babies were born premature.
That's up from 11.6% last year.
It's gained the state a "C" grade on the annual March of Dimes Report Card.
Sara Hart became involved in the March of Dimes the day after her son's short life came to an end.
"It was super important to me to do something to keep his name alive and keep his memory alive. It's something my whole family takes part in, and that's super important to me," Hart said.
The March of Dimes responds to the premature rate news in a statement:
"We expect this to be a one-year blip in our long-term progress toward preventing preterm birth and giving more babies a healthy start in life. The programs and partnerships we have put in place provide the necessary framework for the future of newborn health and we expect to see better rates in the coming years."
Hart is quick to point out all the things she knows the March of Dimes has done to improve lives for mothers with premature children, or to prevent preterm pregnancies.
She tells about a shot that babies will need when they have undeveloped lungs, an advancement directly tied to research funding from the March of Dimes.
"The things that they raise money for, and the research that's done, really do help save lives. And I think it's awesome," Hart said.
And because of her high regard for the March of Dimes, this year Sara Hart is an official Ambassador to that cause.
The next March of Dimes' March for Babies event in St. Joseph is next year, on April 26, at Hyde Park.
Hart says she is still open to having more children.
She takes prenatal vitamins and folic acid, even while she's not pregnant, as measures to have another healthy pregnancy in the future.