The drive, the distance, and the hours were more strenuous than what she’d faced during her previous three pregnancies, cutting into her time for doctors’ appointments. By the time she was five months along, she’d quit the job. “Sometimes I would have to reschedule appointments,” Bacasegua, 31, says. “It didn’t let me enjoy my pregnancy.”

Her son was born—healthy—in 2015. But a new study shows just how risky the added stress of a commute like Bacasegua’s can be for pregnant women.

In a new study published earlier this year, researchers at Lehigh University and the University of Wisconsin-Madison found a link between the distance a woman travels to work every day while pregnant and the health outcomes for her child, including low birth weight, the likelihood of a C-section, and intrauterine growth restriction, or when a baby doesn’t reach a normal size as measured throughout the pregnancy. While previous research has examined how the distance between a woman’s home and her doctor’s office affects the health of her child, this is the first to home in on the daily travel of pregnant women’s commutes.

For pregnant workers who already travel at least 50 miles to work—the Census definition of a long-distance commute—increasing the distance by 10 miles raises the likelihood of low birth weight and intrauterine growth restriction by 0.9 and 0.6 percentage points, respectively. Commuting these kinds of distances every day also increases the likelihood that those carrying a male fetus will deliver via cesarean section (male fetuses have been shown to be more sensitive during pregnancy.)

The authors did not find a link between commuting and pre-term births once they controlled for prenatal visits. But those appointments are one factor that is dramatically affected by commuting, as Bacasegua found. Difficulties making it to prenatal appointments, along with maternal stress, are the two reasons authors Yang Wang and Muzhe Yang identified behind the link between long commutes and adverse infant health outcomes.

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The average woman in the study traveled 64 miles, or about 78 minutes by car, to work. Women in the sample had an average of 11 prenatal doctors’ visits—on the low end of the usual 10-15 range. The average time it took for a woman in this sample to get to the first checkup of her pregnancy was 11 weeks—more than the recommended eight weeks or less. Fifteen percent of the women facing long commutes didn’t make it to a prenatal appointment until after their first trimester, and 4% didn’t go until their third trimester or never made it at all.

Put another way, adding 10 miles to a long-distance commuter’s trip to work can reduce the number of prenatal visits she gets to by 2.5% and increases the number of days between the start date of the pregnancy and a woman’s first prenatal appointment by 2.665 days. Having a long commute decreases the probability that a mother will make it to her first prenatal check-up within her first trimester by 2.4 percentage points. It increases the probability that she’ll never make it to a prenatal doctor’s appointment by 1.5 percentage points.

These conclusions come with some interesting policy implications. Could employers and lawmakers negate the health risks commutes are imposing on their employees and constituents by providing better paid leave before a child is born? Right now, New Jersey and California are the only states that allow mothers to take their parental leave before giving birth. Still, many mothers are reluctant to take time off before they go into labor, wanting to earn every last dollar before being off the job for weeks on often unpaid leave. “If we have a policy where people can take time off before they give birth, we can improve the health of the mother and child,” says Fabiola Santiago, a campaign manager for the paid leave advocacy organization PL+US.

While much attention rightfully focuses on low-income communities and the maternal mortality crisis affecting American black women, this study’s findings cross income brackets. The women studied in this sample are relatively wealthy; they live in zip codes where the average household income is $75,118.40. Many of the women included in the data are likely living far away from their jobs—in suburban or rural communities—by choice. The study analyzed 2014 and 2015 birth records from New Jersey, one of the U.S. states with the longest commute times.

The researchers only measured commutes by distance—not by the time it takes to complete them. So women with shorter (by distance) but possibly more stressful commutes on public transportation are not included in the data.