A 35-year-old postnatal woman, her two daughters, aged two and newborn, spent a night in a closed room with her mother, 59, at their house in the southern province of An Giang on Feb. 1
The next day, neighbors did not see them leave the house and checked on them in the afternoon.
Eventually, they had to break into the house and the bedroom to find all four in critical condition.
The toddler was confirmed dead shortly after while her mother, grandmother and newborn sister were rushed to An Giang General Hospital for emergency aid.
According to local authorities, all four suffered carbon monoxide poisoning from the burning coal.
The 35-year-old woman has followed a practice known as "lying on burning charcoal" or "mother roasting," a traditional postpartum practice in Vietnam and some other parts of Southeast Asia.
This custom involves the new mother lying, sitting, or standing over a bed of burning charcoal or a specially prepared stove.
The belief behind this practice is that the heat from the charcoal helps the mother's body to recover from childbirth, reducing postpartum bleeding, and helping to shrink the uterus back to its pre-pregnancy size.
It is also thought to provide warmth for the mother's body and support the healing of the perineal area, as well as to prevent future health issues attributed to "cold" entering the body during the vulnerable postpartum period.
Many generations of women in Vietnam have followed this practice but these days, with the increasing availability of modern medical practices, "mother roasting" has become controversial.
Tran Van Loi, director of the An Giang General Hospital, said the mother and grandmother were still in the ICU and relying on ventilators.
The newborn, currently being treated at the An Giang Maternity and Children's Hospital, is now in stable condition.
Doctors and experts said when heating or cooking in an enclosed space, oxygen will gradually be consumed. The combustion reaction in the absence of oxygen will form more and more carbon monoxide.
The gas has no smell or color and is very difficult to detect. When someone inhales it, it quickly penetrates the blood and reduces oxygen levels in the blood, causing headaches, dizziness, nausea, chest pain, and confusion.
People who inhale large amounts can pass out and die quickly, especially pregnant women, young children, and the elderly with chronic heart or lung disease.
People with carbon monoxide asphyxia can experience memory loss, decreased concentration, facial muscle paralysis, abnormal movement, difficulty walking, stiff limbs and tremors.