As the Zika virus spreads north from Latin America, Central America and the Caribbean, the list of public health recommendations and scientific unknowns continues to grow. Zika is not new; it was first identified in 1947 in Uganda, and although scientists have found consistent evidence of antibodies in primates since then, few documented cases were reported in humans until recently. Current statistics are grim: the virus has now been confirmed in over thirty countries in the region, with hundreds, perhaps thousands of additional cases likely in the coming months as mosquito season peaks in the Northern Hemisphere.

Although Zika has been linked to a number of health issues, including fever, joint paint, and Guillain-Barré syndrome, most adults who are infected will have mild symptoms, if any, and no lasting effects. The risks for pregnant women, however, are more severe. The virus has been found to cause microcephaly, a condition in which babies are born with abnormally small heads, leading to brain damage and developmental issues. Mounting fears of a virus for which no vaccine or cure exists are prompting increasingly dire warnings from public health agencies, including the World Health Organization, which recommends that pregnant women avoid traveling to areas of ongoing Zika transmission. Officials in a number of affected countries have advised women to postpone pregnancy for a period of months or years; in El Salvador, health ministers have told women not to get pregnant until 2018.

While we know that Zika causes microcephaly, a deeper understanding of the ways in which the virus works is severely lacking. Take the following catalog of unknowns from the website of the Centers for Disease Control:

"If a pregnant woman is exposed

We don't know how likely she is to get Zika.

If a pregnant woman is infected

We don't know how the virus will affect her or her pregnancy
We don't know how likely it is that Zika will pass to her fetus.
We don't know if the fetus is infected, if the fetus will develop birth defects.
We don't know when in pregnancy the infection might cause harm to the fetus.
We don't know whether her baby will have birth defects."

While I’m by no means trying to minimize the implications of having a baby that tests positive for Zika or a child with microcephaly, I find that the uncompromising public health recommendations around the virus’s transmission are a reflection less of the absolute risk to a pregnant woman (which we lack the information to conclusively determine) than of the inadequacy of what medicine can offer in the event of infection. The anxiety surrounding the virus is understandably based in fear and uncertainty, as pregnancy is a 40-week state of perpetual uncertainty that entails a constant balancing of input versus outcome. As with alcohol and caffeine, which pregnant American women are advised to avoid entirely, there is no safe level of exposure to Zika; one must assume that a developing fetus is at risk, even if the mechanism of infection is not fully understood.

I realize that the calculation of risk will be different for women who travel to areas of active Zika transmission and those who reside there. I’m also aware that birth control and abortion are not available to most women in a number of affected countries, including Brazil, and sexual violence and coercion mean that many women are not fully in control of their sexuality. Zika may not be a new disease, but it is a newly emerging threat, and millions of women who are pregnant, thinking of becoming pregnant, or simply of childbearing age will have to weigh questions of risk and responsibility as they make essential decisions about travel and reproduction.