In some of the states hardest hit by the COVID-19 pandemic, doctors are sounding the alarm on a devastating impact the virus may be having on pregnant women: stillbirth.
Reports remain anecdotal, and overall, the total number of stillbirths among pregnant women with COVID-19 appear to be very low. According to the Centers for Disease Control and Prevention, 266 pregnancies have ended in a loss since the start of the pandemic.
Many appear to be concentrated in the Deep South.
In Mississippi, for example, the state health department has identified 72 stillbirths among women with COVID-19 since the pandemic began — more than double what the state would normally expect in the same time period, Dr. Thomas Dobbs, the state's health officer, said this week during a news conference.
"That's quite a number of tragedies that sadly would be preventable," Dobbs said. Nearly all of those mothers, he said, had not been vaccinated against COVID-19.
Mississippi has one of the lowest vaccination rates in the country, with just 39% of residents fully vaccinated. Even before the pandemic, the state had the highest infant mortality rate in the U.S., at more than 9 per 1,000 births.
Whether the apparent trend in Mississippi exemplifies what is happening in other parts of the country remains to be seen.
But physicians in neighboring Alabama, where the vaccination rate is similarly low, have also noticed stillbirth associated with COVID-19 in pregnant women.
At the University of Alabama at Birmingham, the COVID-associated stillbirth rate has ranged from 3% to 6% during the pandemic, said Dr. Akila Subramaniam, an associate professor at the UAB’s Division of Maternal-Fetal Medicine.
That's higher than the usual stillbirth rate seen at her facility, Subramaniam said, which is about 2%. (Nationally, the stillbirth rate is less than 1%, but UAB treats high-risk pregnancies.)
Still, Subramaniam said that the overall number of stillbirths is far too low to draw any cause-and-effect conclusions.
"Everything that we're seeing with stillbirths is truly anecdotal. We don't have the numbers to confirm what we perceive that we're seeing," she said.
It's possible that physicians are seeing an increase in stillbirths only because there are more pregnant women sick with COVID-19, said Dr. Brenna Hughes, chief of the Duke University Medical Center's Division of Maternal Fetal Medicine in Durham, North Carolina.
The super contagious delta variant of COVID-19 has led to a surge in younger adults getting infected, including women of child-bearing age.
According to the CDC, 118,267 cases of COVID-19 have been reported among pregnant women during the pandemic. In recent weeks, ICU doctors have reported an increase in severe cases among unvaccinated pregnant women.
"Since we're seeing more pregnant people getting ill, it's not surprising to me that unfortunately we areseeing a higher rate of fetal losses and stillbirth," Hughes said.
What's the link?
The mechanism behind any apparent link between COVID-19 in pregnant women and fetal death remains unclear. But it is not unusual for infections, such as influenza or syphilis, to affect pregnancies.
"Anytime you have a mom who's really, really sick, the baby is at risk of becoming very, very sick, as well," said Dr. Marc Incerpi, chief of Maternal-Fetal Medicine at Keck Medicine of the University of Southern California.
Incerpi has not seen increases in stillbirths similar to those in Mississippi and Alabama, but has seen a rise in preterm birth in mothers too sick to carry the baby full-term.
Sometimes, Incerpi said, "we have no choice but to deliver them preterm."
There are several aspects of COVID-19 in particular that could explain a possible link between the infection in mothers and poor outcomes in babies.
COVID-19 is known to affect oxygen supply. "If you can't get enough oxygen delivered to the baby, then that increases the risk of bad things happening to babies," Hughes said.
Dr. Cindy Celnik, chief medical officer of the Woman's Hospital of Texas, in Houston, has also seen how COVID-19 can affect a woman's air supply.
"I've never seen young healthy women have to go through this," she said. "It's destroying their lungs."
What's more, the overwhelming inflammation that can occur with severe COVID-19 causes the body to produce nitric oxide, and that, in turn, dilates blood vessels, leading to dangerously low blood pressure in some patients.
And when blood pressure drops too much, "they can't get enough blood flow to the baby. That can cause a stillbirth as well," Hughes said.
There is also emerging evidence that inflammation could affect pregnancies in other ways.
Subramaniam, of UAB, said that her team has detected high levels of white blood cells in the placentas of COVID-19 positive women. These cells are part of the immune system and are associated with inflammation — though she added that much more research is needed to understand the link between the virus, white blood cells and the placenta.
Other research has also observed a link between COVID-19 and inflammation in the placenta. A small study of 50 women, published this month in the American Journal of Obstetrics & Gynecology, found placental inflammation in women with the virus.
One of the study's authors, Dr. Christopher Golden, a neonatologist at Johns Hopkins Medicine, said it appeared that the risk for COVID-related complications was higher later in pregnancy.
"If you are infected at the time that you were about to deliver, there's an increased risk of multiple perinatal complications," Golden said. "Stillbirth is one of them."
Experts have underscored that the COVID-19 vaccine can prevent these complications; virtually all of the COVID-positive pregnant women who experienced complications had not been vaccinated.
The COVID-19 vaccines have been shown to be safe in pregnant women and their babies, and do not increase the risk of miscarriage or stillbirth.
"The vaccine could actually save your baby," Hughes said.
This story was originally published on NBC News.