The world's smallest mother is testing the limits of her fragile body, giving birth to a third baby and considering another pregnancy despite doctors' advice against ever having children.
The genetic disorder has caused multiple fractures in her bones that have stunted her growth and confined her most of the time to a wheelchair.
Doctors say Herald should never have risked having children. Her pelvis is so small and deformed that the growing fetus could have crushed her lungs, heart and spine.
And with a 50-50 chance of passing the genetic disorder on to her children, Herald's developing babies might also have been put at risk.
"Medically it's not physically or logically possible, it's all from the grace of God," said Herald, who is still undecided about a fourth pregnancy.
"Yeah, we're done," she said. "But we have other days when we're not ready to call it quits yet."
Together, Herald and her husband Wil Herald are raising Kateri, 3, Makaya, 2, and Malachi, who is only 7 months old. The oldest and youngest have OI, but the middle daughter is average height and now stands a foot taller than her mother.
Malachi was delivered by Caesarian section in November and was only 5 inches long, weighing in at only 2 pounds, 10 ounces.
He was just released from the hospital in April after getting a virus that overpowered his delicate respiratory system and having hernia surgery.
Though Herald's decision to bear children flies in the face of medical recommendations, she said, "I think it's great and it's something to be proud about."
The hallmark of osteogenesis imperfecta is bones that break easily, but it is also characterized by fragile connective tissue, skin and blood vessels, making all the body's organs more vulnerable, according to the Osteogenesis Imperfecta Foundation.
The organization is raising awareness of the disorder that affects 30,000 to 50,000 Americans at a conference of doctors, researchers and patients this week in Portland, Ore.
The genetic disorder is caused by a mutation in one of the genes for collagen, the most common protein in the body, responsible for lung strength. Those with the most serious form often have respiratory problems and are at high risk for asthma.
Doctors can treat the bone density with bisphosphonates and sometime insert rods to lengthen and straighten deformed limbs.
Out of roughly eight different types of the disorder, Herald has Type 3, the severest form other than Type 2, which is fatal, usually at birth.
About half of all patients have a moderate form of the disorder and are taller in stature. Those with Type 3 are usually under 3-feet tall.
"They have dozens if not hundreds of fractures in their lifetime," said Dr. Bradley Tinkle, a clinical geneticist and director of the Skeletal Dysplasia Clinic at Cincinnati Children's Medical Center, who has treated Herald but would not speak directly to her case.
"A lot of them are born with a dozen fractures at the very beginning, so a diaper change or a blood pressure cuff can break bones," he said. "It doesn't take a lot to do something to cause a fracture."
Because bones are busy repairing breaks, they do not grow properly and are often malformed. Those with OI can expect a normal life span.