Puerto Rico Births Projected to Decline

Puerto Rico is expecting about 1,000 fewer babies to be born this year than originally forecast, due in part to the Zika virus, a government official said Thursday.

“Given the introduction of Zika, we had to revise our expected live birth numbers and right now we are expecting a little bit over 27,000, which is about 1,000 less than what we had envisioned,” Brenda Rivera-Garcia, the territory’s epidemiologist, said in an interview following a presentation at the annual meeting of the American Society of Tropical Medicine and Hygiene here.

Birth data offer potential clues about how women of childbearing age across the Americas and beyond are responding to the threat of Zika, a mild virus that can nevertheless cause devastating birth defects in the fetuses of those who become infected while pregnant.

As the mosquito-borne virus has spread rapidly over the past two years through the Western hemisphere, researchers and public health officials have wondered whether women would delay pregnancies or abort their fetuses if they became pregnant.

Dr. Rivera-Garcia, a leader of the Zika response at the Puerto Rico Department of Health, said it isn’t clear how many women on the island are delaying pregnancy or aborting fetuses. The department doesn’t currently have enough staff to track that data, she said.

Since the outbreak began late last year, at least 2,615 pregnant women had been confirmed infected with Zika, according to the Puerto Rico Department of Health. Three babies have been born with Zika-related birth defects.

The total number of babies born has been on the decline in Puerto Rico for several years, as residents of the island territory have moved to the U.S. mainland to escape a crippling economic crisis. The continuing exodus factors into the expected decline in births this year, Dr. Rivera-Garcia said.

There were 34,434 babies born in Puerto Rico in 2014, according to the U.S. Centers for Disease Control and Prevention, and 31,272 babies born in 2015, according to preliminary CDC data.

Questions about how Zika may be affecting birthrates have emerged over the past few months. While more than 2,100 babies in Brazil have been born with confirmed Zika-related birth defects, other countries are reporting far fewer cases. One hypothesis is that women in Brazil were caught off guard by the virus, whose effects on fetuses were unknown until their babies were born.

Women in other countries such as Colombia, where 57 cases have been reported thus far, had advance warning. In addition, abortion is legal in Colombia and some other countries, unlike Brazil.

Puerto Rico, hard hit by Zika, has confirmed 33,455 cases of Zika infection since November 2015. The current epidemic appears to have peaked in late summer.

Tyler Sharp, epidemiologist in the CDC’s dengue branch in Puerto Rico, said in an interview that the CDC still expects 15% to 18% of the island’s population of about 3.5 million to have been infected by the end of this year. That is down from the CDC’s original projection that 25% of the population would be infected by the end of the year.

Most pregnant women in Puerto Rico have been infected in their third trimester, when the risk of birth defects is considered lower. Dr. Rivera-Garcia said. “We still haven’t seen those births from the peak of transmission,” she said. “So it isn’t that we’re not going to see cases, it’s just that we’re not seeing them yet. Whether we’ll see them in the large numbers that other jurisdictions have seen them in, that’s still a big question mark.”

Write to Betsy McKay at betsy.mckay@wsj.com

By BETSY MCKAY

Threat of Zika virus, effects of an economic exodus weigh on island’s forecasts

Puerto Rico Births Projected to Decline