After the city announced last week that it’s found 390 cases of the measles in the Big Apple, including two pregnant women, there’s growing concern about a disease long believed to have been all but eradicated.

Expecting moms — along with those who got vaccinated before 1989 and might not have received any booster shots — are especially worried.

“We’ve seen a lot of [pregnant] women coming in with that concern … that their immunity has waned over time,” said Dr. Ashley Roman, director of maternal fetal medicine at NYU Langone, adding that the disease could lead to early labor and a low birth weights.

Plus, she said, doctors can’t administer the vaccine to pregnant women because it uses weakened live viruses to build resistance to measles, as well as mumps and rubella.

At-risk moms can get an MMR booster after delivery, but their babies aren’t safe to receive the vaccine until 6 months of age.

Some are going so far as to quarantine their young families.

New mother Julia Erenkrantz has all but isolated her 3-week-old son inside their Columbus Circle apartment.

“My kid has only been to an indoor space that wasn’t our apartment building two times since he left the hospital, and that’s been to the pediatrician’s office,” said the 32-year-old, who plans on vaccinating her son as soon as he turns 6 months.

Josh Young, who has a 12-week-old baby with fellow Broadway actor Emily Padgett, feels the same.

“We won’t bring our daughter into the city, we won’t take her on the train — it’s just not worth it,” said the 38-year-old, who lives in South Orange, NJ.

Katie Franklin had assumed she couldn’t catch the measles. After all, the 32-year-old Jersey City resident got the MMR vaccine when she was young.

Then she heard from other pregnant women her age who said they were getting blood tests after realizing they may no longer be inoculated against the disease.

“I have no idea if I’m immune,” said Franklin, who is three months pregnant.

Since commuting into Midtown every day for her IT job puts her — and her unborn child — at risk, she prefers to take the bus instead of the subway, hoping it minimizes her exposure to crowded spaces and germ-infested poles and surfaces.

“I don’t know what effects [getting the measles] could have on me or the fetus at this stage, but it’s highly contagious,” Franklin told The Post. “It’s really scary.”

This after the city’s Department of Health increased this week its number of confirmed cases to 390 from 374 just two days earlier.

And the Centers for Disease Control said anyone who had an MMR shot before 1989 — and likely would have only received only one dose of the vaccine — should get a booster shot as two injections are now recommended.

Doctors are telling those who can’t get the MMR vaccine — pregnant women, newborns and individuals with severely weakened immune systems — to stay away from crowded areas, neighborhoods with clustered outbreaks (including Williamsburg and
Borough Park) and anyone who is coughing or looks ill.

But as any New Yorker can tell you, that’s not always easy living in the Big Apple.

“What frightens me most is that the people who are choosing not to vaccinate are not the ones paying the consequences,” said Erenkrantz. “It’s their children, it’s the vulnerable, it’s the sick, it’s the people around them.”