From 1915 through the 1990s, amid vast improvements in hygiene, nutrition, living conditions and health care, the number of babies of all races who died in the first year of life dropped by over 90 percent — a decrease unparalleled by reductions in other causes of death. But that national decline in infant mortality has since slowed. In 1960, the United States was ranked 12th among developed countries in infant mortality. Since then, with its rate largely driven by the deaths of black babies, the United States has fallen behind and now ranks 32nd out of the 35 wealthiest nations. Low birth weight is a key factor in infant death, and a new report released in March by the Robert Wood Johnson Foundation and the University of Wisconsin suggests that the number of low-birth-weight babies born in the United States — also driven by the data for black babies — has inched up for the first time in a decade.

Black infants in America are now more than twice as likely to die as white infants — 11.3 per 1,000 black babies, compared with 4.9 per 1,000 white babies, according to the most recent government data — a racial disparity that is actually wider than in 1850, 15 years before the end of slavery, when most black women were considered chattel. In one year, that racial gap adds up to more than 4,000 lost black babies. Education and income offer little protection. In fact, a black woman with an advanced degree is more likely to lose her baby than a white woman with less than an eighth-grade education.

This tragedy of black infant mortality is intimately intertwined with another tragedy: a crisis of death and near death in black mothers themselves. The United States is one of only 13 countries in the world where the rate of maternal mortality — the death of a woman related to pregnancy or childbirth up to a year after the end of pregnancy — is now worse than it was 25 years ago. Each year, an estimated 700 to 900 maternal deaths occur in the United States. In addition, the C.D.C. reports more than 50,000 potentially preventable near-deaths, like Landrum’s, per year — a number that rose nearly 200 percent from 1993 to 2014, the last year for which statistics are available. Black women are three to four times as likely to die from pregnancy-related causes as their white counterparts, according to the C.D.C. — a disproportionate rate that is higher than that of Mexico, where nearly half the population lives in poverty — and as with infants, the high numbers for black women drive the national numbers.

Monica Simpson is the executive director of SisterSong, the country’s largest organization dedicated to reproductive justice for women of color, and a member of the Black Mamas Matter Alliance, an advocacy group. In 2014, she testified in Geneva before the United Nations Committee on the Elimination of Racial Discrimination, saying that the United States, by failing to address the crisis in black maternal mortality, was violating an international human rights treaty. After her testimony, the committee called on the United States to “eliminate racial disparities in the field of sexual and reproductive health and standardize the data-collection system on maternal and infant deaths in all states to effectively identify and address the causes of disparities in maternal- and infant-mortality rates.” No such measures have been forthcoming. Only about half the states and a few cities maintain maternal-mortality review boards to analyze individual cases of pregnancy-related deaths. There has not been an official federal count of deaths related to pregnancy in more than 10 years. An effort to standardize the national count has been financed in part by contributions from Merck for Mothers, a program of the pharmaceutical company, to the CDC Foundation.

The crisis of maternal death and near-death also persists for black women across class lines. This year, the tennis star Serena Williams shared in Vogue the story of the birth of her first child and in further detail in a Facebook post. The day after delivering her daughter, Alexis Olympia, via C-section in September, Williams experienced a pulmonary embolism, the sudden blockage of an artery in the lung by a blood clot. Though she had a history of this disorder and was gasping for breath, she says medical personnel initially ignored her concerns. Though Williams should have been able to count on the most attentive health care in the world, her medical team seems to have been unprepared to monitor her for complications after her cesarean, including blood clots, one of the most common side effects of C-sections. Even after she received treatment, her problems continued; coughing, triggered by the embolism, caused her C-section wound to rupture. When she returned to surgery, physicians discovered a large hematoma, or collection of blood, in her abdomen, which required more surgery. Williams, 36, spent the first six weeks of her baby’s life bedridden.

The reasons for the black-white divide in both infant and maternal mortality have been debated by researchers and doctors for more than two decades. But recently there has been growing acceptance of what has largely been, for the medical establishment, a shocking idea: For black women in America, an inescapable atmosphere of societal and systemic racism can create a kind of toxic physiological stress, resulting in conditions — including hypertension and pre-eclampsia — that lead directly to higher rates of infant and maternal death. And that societal racism is further expressed in a pervasive, longstanding racial bias in health care — including the dismissal of legitimate concerns and symptoms — that can help explain poor birth outcomes even in the case of black women with the most advantages.