At least two pregnant women in the United States infected with the Zika virus have chosen to have abortions in recent months, the Centers for Disease Control and Prevention reported Friday, while two others have suffered miscarriages. One woman gave birth to an infant with serious birth defects, while two others delivered healthy infants. Two are still pregnant.

The varied outcomes of nine pregnant U.S. women the agency has identified with Zika, as well as the hundreds of U.S. women that have sought out tests for the virus, underscore the angst and uncertainty that the diseases is causing as it spreads through much of the Americas, particularly when it comes to worries over severe birth defects associated with illness.

Everything you ever wanted to know about the Zika virus and its spread across North and South America. (Daron Taylor, Claritza Jimenez/The Washington Post)

One of the women who had an abortion was in her 30s and had contracted the virus during her first trimester while traveling to a Zika-affected area, the agency said. When she was 20 weeks pregnant, she learned from an ultrasound that her fetus was suffering from severe brain abnormalities. Doctors also tested her amniotic fluid and found the presence of Zika virus. "After discussion with her health-care providers, the patient elected to terminate her pregnancy," the CDC wrote in a case study released Friday. Officials did not offer details surrounding the second abortion, other than to say it involved another woman who had become infected with Zika during the first trimester of her pregnancy.

The agency said that between last August and Feb. 10, it received more than 257 requests for Zika virus testing of pregnant women in the United States. The vast majority of those cases, 97 percent, tested negative for the disease. But the CDC has been tracking nine pregnant women in the country who tested positive for Zika. All had reported symptoms of the disease — such as fever, rash, joint pain and conjunctivitis — and all had traveled to one of more than two-dozen Zika-affected countries, officials said.

Denise Jamieson, a CDC researcher helping oversee the agency’s response to the outbreak, said the number of brain abnormalities observed among the small group of pregnant women with Zika was higher than experts would have expected.

Six of the infected women acquired Zika during their first trimester, the CDC reported. Of those, two experienced miscarriages and two chose to have abortions. One woman delivered a baby who suffered from "severe microcephaly," a condition marked by abnormally small head size, as well as seizures, trouble swallowing, eye problems and calcifications in the brain. One pregnancy is ongoing, the CDC said. The agency said that while remnants of the Zika virus were detected in fetal tissues taken after both miscarriages, "it is not known whether Zika virus infection caused the pregnancy losses." Roughly 10 to 20 percent of all pregnant women suffer miscarriages during the first trimester, officials noted.

Of the two pregnant women with Zika diagnosed during their second trimester, one gave birth to an apparently healthy baby and another is still pregnant. The one pregnant woman who experienced Zika symptoms during her third trimester later delivered a healthy infant.

Friday's report adds another dimension to the ongoing efforts by scientists in the United States and abroad to answer some of the many mysteries surrounding the once-obscure Zika virus. At the top of that list is determining whether — and how — the virus is linked to birth defects such as microcephaly, as well as to cases of a rare autoimmune disorder known as Guillain-Barré Syndrome. Those associations, particularly to possible problems in newborns, appear to be growing more likely over time.

"The evidence every week is accumulating and getting stronger and stronger," Anthony Fauci, director of the National Institutes for Allergy and Infectious Diseases, told lawmakers at a Senate hearing this week.

CDC director Tom Frieden said Friday that scientists are confident that there is an association between the Zika virus and microcephaly. But there is much they still don't understand, such as why the risks are higher at certain points during pregnancy and whether there are other factors that can influence the likelihood of birth defects. He said researchers have undertaken studies to answer some of those questions in Brazil, where the number of microcephaly cases is highest.

"There are many things we wish we knew and are working hard to find out," Frieden said. "This is an extraordinarily unusual occurrence.  ... Part of science is uncovering information step by step, trying to be sure not to overstate what the data shows."

Frieden said Friday that the United States has 147 reported Zika cases in 24 states and the District, most related to people who traveled to areas affected by the virus.

But Friday's CDC report also highlights the hard questions that pregnant women face when they have been infected with the Zika virus, not to mention the religious and societal debates that have unfolded as the epidemic has spread.

Throughout Latin America, home to some of the most restrictive abortion laws in the world, there have been controversial calls to lighten restrictions on the practice in the face of the Zika virus outbreak. In El Salvador, where abortion is banned, the health minister has argued for a revision of the law because of the dangers the virus poses to fetal development. In Colombia and Brazil, there have been efforts to lift certain restrictions on abortions as the virus has spread explosively through the continent, but those efforts have encountered stiff opposition, particularly from religious authorities.

Pope Francis himself has waded into the issue, saying recently that the use of contraceptives may be morally acceptable in fighting the Zika virus. He cited the decision in the 1960s by Pope Paul VI, who allowed nuns in Belgian Congo to use artificial contraception to prevent pregnancies because they were being systematically raped. But Francis stopped short of saying abortion should be condoned.

“Abortion isn’t a lesser evil, it’s a crime,” he told reporters earlier this month. “Taking one life to save another, that’s what the Mafia does. It’s a crime. It’s an absolute evil.”

The explosive spread of Zika has raised the spectre of the crisis in birth defects in the 1960s. During that decade, thousands of children were born with malformed limbs after their mothers were prescribed thalidomide, which had been marketed as a mild sleeping pill. And an estimated 20,000 other babies were born with issues related to the eyes, ears, heart and other organs after their mothers became infected with German measles or rubella.

Both those crises are considered critical to shifting public opinion about whether abortion should be legal at a time when the merits of Roe v. Wade were being debated.

Of the estimated 700,000 legal abortions that take place in the United States each year, only a small percentage are believed to be due to birth defects. While providers are not required to track information about why women choose the procedure, a 2004 survey by the Guttmacher Institute found that only 13 percent made their decision because of possible problems impacting the fetus. (The vast majority of the rest said it was because a baby would dramatically change their life or they couldn’t afford to have a child.)

Richard Beigi, chief medical officer of Magee-Womens Hospital of University of Pittsburgh Medical Center, who recently wrote a JAMA opinion piece on Zika, said the CDC report reinforces fears that many pregnant woman already have but does not provide any answers.

While the CDC recommends increased surveillance starting at 18 to 20 weeks for women suspected of having a Zika infection, there is little a woman can do at that time except psychologically prepare for the child or choose to terminate the pregnancy if there is suspected microcephaly.

“The big challenge right now is we don’t have any interventions,” Beigi said.

Women considering abortions related to Zika face an ethical dilemma that can be very different from those whose babies have other types of birth defects. Unlike like chromosomal issues that can be detected in the womb with a very high degree of certainty, the initial diagnosis and a child’s long-term trajectory can be less clear cut with microcephaly.

Ultrasounds can show whether a child’s head is growing abnormally small, but the cut-off for a child having microcephaly is arbitrary and varies by region. Moreover, while head size does sometimes correlate with the severity of the impact, that is not always the case. Experts have estimated that as many as 10 to 15 percent of people diagnosed with the condition at birth do not have any intellectual impairment or other issues related to it.

Ganeshwaran Mochida, a neurologist at Boston Children’s, said that pregnant women suspected of being infected with Zika may also consider getting fetal MRIs which can provide more detailed pictures and better guesses about whether the microcephaly is accompanied by a brain defect. Mochida emphasized that while the prognosis of Zika babies with microcephaly may not seem so hopeful in some cases, it's important to keep in mind that children’s brains are “still very plastic.”

"Even if certain parts are damaged or underdeveloped,” Mochida said, “sometimes with enough intervention early on we are surprised how much they are capable of.”

This post has been updated. 

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