(CNN) -- The room was lined with baby after baby, and it was almost too warm for Keri Dykes to tolerate.
She remembers squeezing between the incubators to see her son Jesse, who had been born only 25 weeks into her pregnancy.
A neonatal intensive care unit in Tupelo, Mississippi, is where Jesse spent his brief life in 2008 -- a life cut short by an infection that got into his bloodstream and lungs.
The first time Dykes, 29, got to hold him and look at him face to face, she remembers that his pretty blue eyes were open as he was dying.
"It's just something you never, ever think will happen to you," she said.
Jesse happened to be born in the state where babies are less likely to reach their first birthday than in any other state, according to the most recent data (PDF) from the Centers for Disease Control and Prevention.
For every 1,000 Mississippi babies born in 2011, 9.4 died before their first birthday, according to the state's health office. That makes Mississippi's infant mortality rate more comparable to countries such as Costa Rica (9.2), Sri Lanka (9.5) and Botswana (10.5) than the United States (6.0), according to latest estimates in the CIA World Factbook.
The bottom of the list
Mississippi is 50th out of 50 states when it comes to infant mortality, and it's been that way for a long time, says state health officer Mary Currier.
There's not one clear explanation. Experts cite a multitude of factors that are also seen in other parts of the country and around the world.
For example, Mississippi leads the nation in obesity, which can carry with it a host of complications that might affect a baby, such as hypertensive disorders, says Dr. Michelle Owens, an obstetrician-gynecologist at the University of Mississippi Medical Center. Other Southern states with a high prevalence of obesity -- Alabama and Louisiana, for instance -- also have some of the nation's highest rates for infant mortality. A 2010 study also found that overweight and obese women are at higher risk for preterm birth.
In general, Owens said, many pregnant women don't realize the importance of getting their own medical problems treated.
"We know that the way we get the best pregnancy is to have a healthy mom before mom and baby are together," she said.
Birth defects are the leading cause of infant death in the United States. Not all are preventable, but a mother can reduce risk by keeping her own health under control by eliminating smoking, drinking and illegal drugs.
The same is true for premature births, another leading cause of infant deaths in the United States. The March of Dimes recently released its Premature Birth Report Card and gave failing grades to Mississippi, Alabama and Louisiana. Mississippi has the largest premature birth rate based on the 2011 national statistics used in the report.
Poverty, low socioeconomic background and low education contribute to high preterm birth rates, said Dr. Eve Lackritz, senior program officer for the Global Alliance to Prevent Prematurity and Stillbirth, an initiative of Seattle Children's. Lackritz was once the branch chief for the CDC's maternal and infant health division.
Southern states tend to have some of the biggest poverty problems in the country. Mississippi led the country with the highest percentage of people whose income was below the poverty line in 2011, according to the American Community Survey (PDF).
"Infant mortality goes along with poverty, and we have a pretty low average income in the state," says Currier.
Mississippi also ranks in the top 10 states for the percent of the population that is uninsured (19%), according to the Kaiser Family Foundation, and in the proportion of residents receiving Medicaid (20%).
Teenage births are also more common in the South than in most other parts of the country, according to the latest CDC data. Mississippi had the highest teen birth rate in the country in 2010, at 55 births per 1,000 women compared with a national average of 34.2. Alabama (43.6) and Louisiana (47.7) are also on the higher side in this regard.
Babies born to teens are more likely to be born prematurely and have a low birth weight, according to the Mayo Clinic. Not receiving proper prenatal care contributes to the complications that can arise in teen pregnancies.
An international reach
The interplay between teenage births, poverty and infant mortality isn't unique to the United States.
Catalina Escobar, one of the top 10 CNN Heroes of 2012, knows all too well how much young mothers need medical support and education to give birth to healthy children. In Escobar's country, Colombia, the infant mortality rate is 15.92, much higher than any state in the U.S.
Colombia's colorful city of Cartagena is an attractive tourist destination, with its historical grandeur and beach resorts. Acclaimed author Gabriel Garcia Marquez set one of his famous novels, "Love in the Time of Cholera," there. But Cartagena has a darker side that visitors may not realize: One-third of residents live at or below the poverty line.
Escobar once worked in a maternity clinic in Cartagena, and she was devastated when a 12-day-old baby died in her arms. It was heartbreaking, Escobar said, even more so when she found out that the baby's teenage mother couldn't afford $30 for treatment that could have saved the baby's life.
"His mother (needed) $30 that I had in my pocket. I will never forget that," she said. "It was a preventable death."
To break the cycle of poverty and infant deaths, she started the Juan Felipe Gomez Foundation, which is helping young mothers in Cartagena. Since 2002, her foundation has provided counseling, education and job training to more than 2,000 teenage mothers. And in 2005, she established a medical clinic that has provided health care to more than 84,000 low-income people -- mostly young mothers and their children.
"You see these girls, (with) their tiny faces ... they're babies holding babies," Escobar said.
What role does race play?
Colombia has a much higher infant mortality rate than the United States as a whole, but not when you examine the vast differences among racial groups in the U.S.
CDC data spanning from 2006 to 2008 show that black Americans in Hawaii, Indiana, Ohio, Tennessee and Wisconsin all have infant mortality rates above 15 per 1,000 live births. This racial disparity is very much present in Mississippi, too, where the rate over that period was 7.07 for white children compared with 13.82 for black children.
"It is my belief that is largely due to poverty and the social determinants of health," Currier said about this divide.
In Mississippi, 40% of infants are born to black women, which could be driving up the infant mortality rate for the state as a whole, Lackritz said. Black women are also 50% more likely to give birth to a premature baby, and no one knows why, the CDC says.
These demographic observations don't have to do with skin pigment, Lackritz said, but rather associated factors such as poverty, low socioeconomic background and teen births.
The disparities seem to persist even taking into account health conditions such as diabetes and obesity, Owens said. There is even evidence, including a study from Morehouse School of Medicine, that black women with college degrees have a higher likelihood of preterm birth and low birth weight than white women with college degrees.
It's unknown whether there are genetic factors that come into play, or if there are higher rates of inflammation or infection among blacks linked to pregnancy complications. There might be an interaction between a person's genetic disposition and exposure to stress that could lead to preterm births, Lackritz said.
There could be environmental factors, including stress, that certain groups may experience in a different way, Owens said.
"This should be an active area of research," Lackritz said. "This is an area that has not received the sufficient attention that it deserves."
Sudden infant death syndrome
It's also still a mystery as to why rates for black children are disproportionately higher for sudden infant death syndrome, or SIDS, than white babies. SIDS is the name for any unexplained sudden death in an infant less than 1 year old.
SIDS is the leading cause of death for children between 1 and 12 months and the third most common cause of infant mortality in general in the United States.
Public health authorities have issued recommendations about how babies should sleep to reduce the risk of SIDS. A national campaign called Safe to Sleep (formerly known as Back to Sleep) encourages parents to keep their babies sleeping on their backs, on a firm surface, and in a room of comfortable temperature.
Thanks in part to this campaign, SIDS deaths have declined by more than half since 1994. But the rates remain significantly higher for some demographic groups, including blacks. Deaths from SIDS in 2008 nationally were 55.4 per 100,000 live births in 2008, according to the National SUID/SIDS Resource Center, and for whites it was similar at 54.6. For blacks, however, it was 106.7.
Anitra Cooper of Jackson, Mississippi, had a son, Alex, who died suddenly at 3 months and 1 day old. It might have been because of sleeping on his stomach, but there's no way to know for sure.
"I was still breast-feeding him at the time," Cooper said. "I was doing everything that I could possibly do."
Cooper, who is black, did not know the extent of the country's racial divide in infant mortality until CNN told her how much more common infant deaths are among black children than white children.
She speculated that one factor may be that some women may leave their doctor's office without getting the information they need.
"A lot of people go to the doctor and don't make the doctor talk in layman's terms," Cooper said. "They're unaware of what they need to do for their children."
In the meantime, researchers are searching for evidence-based recommendations so that pregnant mothers can prevent preterm births and therefore reduce the risk of infant mortality. Currently, says Lackritz, there aren't any known interventions (beyond staying in good health and not smoking, drinking or using drugs) that would have a far-reaching impact on the entire population.
The hormone progesterone is used in an intramuscular injection, called 17 alpha-hydroxyprogesterone caproate, which may reduce risk in women who have given birth prematurely before.
"If we can increase access to that injectable medication, that can decrease preterm birth," said Currier, the Mississippi health officer.
Dykes received this injection with her next two children, whom she nearly carried nearly to full term although she had to have planned Caesarean sections with them.
Other methods for preventing preterm births have not proved useful scientifically. The American College of Obstetricians and Gynecologists says bed rest, hydration and pelvic rest do not appear to improve the rate of preterm birth and should not be routinely recommended.
Mississippi's infant mortality rate, although still the highest in the country, is slightly lower than it has ever been for the state, Currier said. The dip isn't statistically significant, but "at least we're going in the right direction," she said.
Cooper and Dykes both said they did everything right before giving birth to infants who died. They got all the prenatal care and education they needed. Neither woman was a teenager during pregnancy. They both work, and so do their husbands. They both have health insurance.
So the search for answers about infant mortality trends continues. The Dykes family tries to raise awareness for the cause through the March of Dimes, participating in the March of Dimes Walk to raise money in Jesse's memory.
Cooper now volunteers with the Mississippi SIDS Alliance to spread awareness. Such organizations exist, she says, not only for educational outreach, but "so that we can be strong and move on, and go through the proper stages of grief."
Both women are also strong in their faith.
"We just pretty much believe that God had a purpose for (Jesse), and he did touch a lot of lives while he was here," Dykes said. "We just have to believe that we don't have to understand."
CNN's Kathleen Toner contributed to this report.