The fertility rate in Flint, Mich., dropped precipitously after the city decided to switch to lead-poisoned Flint River water in 2014, according to a new working paper.

That decline was primarily driven by what the authors call a “culling of the least healthy fetuses” resulting in a “horrifyingly large” increase in fetal deaths and miscarriages. The paper estimates that among the babies conceived from November 2013 through March 2015, “between 198 and 276 more children would have been born had Flint not enacted the switch in water,” according to health economists Daniel Grossman of West Virginia University and David Slusky of Kansas University.

In April 2014, Flint decided to draw its public water supply from the Flint River, a temporary measure intended to save costs while the city worked on a permanent pipeline project. Residents immediately began complaining about the odor and appearance of the water, but well into 2015 the city said that the water was safe.

Subsequent testing by Flint authorities and outside agencies turned up lead levels that in some cases were dozens or hundreds times higher than the Environmental Protection Agency’s safety threshold. A September 2015 study showed that the proportion of Flint children with high lead levels in their blood had roughly doubled after the water change. The city finally switched back to Lake Huron water in October 2015.

The harmful effects of lead exposure on children’s health are well-documented. They include cognitive deficiencies, lower educational attainment, and a host of problems affecting the brain, kidneys and liver.

Less well-known are lead’s effects on fetal health. Literature reviewed by Grossman and Slusky showed that maternal lead exposure is linked to “fetal death, prenatal growth abnormalities, reduced gestational period, and reduced birth weight.”

Grossman and Slusky compared birth and fetal death rates in Flint with those in other Michigan cities.

“These areas provide a natural control group for Flint in that they are economically similar areas and, with the exception of the change in water supply, followed similar trends in fertility and birth outcomes over this time period,” the authors said.

They found “a substantial decrease in fertility rates in Flint for births conceived around October 2013, which persisted through the end of 2015. Flint switched its water source in April 2014, meaning these births would have been exposed to this new water for a substantial period in utero.” Other cities showed no drop.

During this time period, residents in Flint were generally unaware of the amount of lead in their water. “Because the higher lead content of the new water supply was unknown at the time, this decrease in [the general fertility rate] is likely a reflection of an increase in fetal deaths and miscarriages and not a behavior change in sexual behavior related to conception like contraceptive use,” Grossman and Slusky concluded.

They also found that “fetal death rates increased in Flint but did not change substantially in other areas following the water change.” The change amounted to a 58 percent increase in fetal deaths, which the authors called “horrifyingly large.”