Relative Risks and Reasonable Responses to the Zika Virus in Pregnancy – Part 1

By Rebekah Wheeler, RN, CNM, MPH


The Zika virus and its potential effect on pregnant people have been hot topics for the past several weeks.  News headlines, health alerts, social media and more have been busy offering up information and suggestions about this virus that no one seemed to know about before 2016.  Filtering fact from fiction and fear mongering is important and childbirth educators and other birth professionals are in a great position to share evidence based information and facts with the families they work with.  In a two part post series on the Zika virus and risk, Certified Nurse Midwife and public health specialist Rebekah Wheeler shares information about what exactly is the Zika virus – providing all the facts about what it is and what it isn’t and then in her second post on Thursday, shares how you can talk about this risk in relation to other known risks that may affect pregnant people.  After our short series ends, you should feel confident in understanding the basics of the Zika virus, what families can do to reduce their risk and how to understand those risks in relation to other risks they may also face.  – Sharon Muza, Community Manager, Science & Sensibility

Although Zika is everywhere in the news these days, confusion about what it is, what it does, and what to do about it is widespread.  As one tries to follow the news on Zika, they encounter advice for pregnant people ranging from “avoid travel to affected areas” to “everyone who can become pregnant anywhere are at risk.” It can feel alarming to families and professionals alike.  Many soon-to-be parents feel anxious with the uncertainty.  I am a Certified Nurse Midwife  (CNM) who has been faced with terrified patients, and I want to help them have a realistic sense of how much risk Zika might pose to their babies’ health.  I am also a former public health researcher with a background in international women’s health, dedicated to parsing the data closely to figure out what we really know about Zika and pregnancy.  Lastly, I am a pregnant woman, and I want to know whether and how much to worry myself.

        Thus, I’ve been triply motivated to track the recommendations from the Centers for Disease Control (CDC) and filter the fear-mongering on the local news.  This two part article seeks to provide a summary of the state of the current understanding of Zika, while also putting the risk into perspective by comparing it to other well-known diseases that can affect pregnancies.  It also seeks to separate out what we know and do not know about Zika, and to dispel myths about the disease.  Let’s begin with the basics.

What We Know About Zika

The Zika virus was first identified nearly 70 years ago in Uganda, and has never previously been thought to pose a major public health threat.  Over the decades, there have been numerous outbreaks infecting tens of thousands of people across the world, and no cases of microcephaly (babies born with abnormally small heads and corresponding learning and developmental problems) have ever previously been reported.  The most recent outbreak in Brazil is the first time we’ve seen a significant rise in microcephaly among babies born to women who also had Zika in their bloodstream.

Zika is a mild viral infection, and the CDC states that 80% of those who get it never feel any symptoms. Part of why most have never heard of it before is that it has been thought to be relatively harmless. When people do show effects from the virus, they are usually quite mild, present up to two weeks after exposure, and last less than a week. Severe disease requiring hospitalization is uncommon. No evidence exists to suggest that pregnant people are more likely to get the Zika virus or experience the disease more severely.  Documented symptoms of Zika, when symptoms are even present at all, are:

  • Mild fever (100-102 F)
  • Rash (usually not itchy)
  • Joint and muscle pain (known as arthralgia)
  • Red eyes (known as conjunctivitis, usually without the discharge of pus we usually associate with this)

Almost all known cases of Zika infection have occurred in Central America, South America, the Caribbean and the Pacific Islands.  Go the CDC website for the most up to date list of affected countries.  A few cases have been documented in other places, including Texas and Hawaii, but it is believed that all of these individuals were infected in one of the above countries before flying back to the US.  The CDC has made a list of affected countries and territories, but be aware that it doesn’t mean that the whole country is crawling with Zika.  For example, cases in Mexico have thus far been confined to very rural areas not frequented by tourists, with zero cases reported in beach resort towns US visitors are more likely to visit.  Virtually every case of Zika was spread by a well-known specific species of mosquito known as the aedes aegypti.

There have now been confirmed cases of a woman getting Zika from her male partner through sexual contact, but each was within the initial two weeks after the male partner’s exposure to the disease, while the virus is active in the bloodstream.  No cases of sexual transmission have been documented beyond the acute exposure period, so we don’t currently think Zika can be dormant in the bloodstream and spread to others, like HIV can be.

Zika and Microcephaly

The reason expectant families are following this story at all is because the Zika virus has been linked to cases of microcephaly, which as I mentioned before, is a serious condition in which a baby is born with an abnormally small head and brain damage, which every pregnant person would understandably want to avoid if possible.  Here’s why Zika has been linked to cases of microcephaly all of a sudden.  There was a Zika outbreak in Brazil in 2015, with between 500,000 and 1,500,000 Brazilians getting the virus (FRAMEWORK, S. R. 2016).  At the same time, local health officials in northern Brazil noticed that there was a sharp increase in rates of microcephaly. Brazil usually sees about 150 cases of microcephaly each year, but in 2015 that number was above 3,000, a massive increase (FRAMEWORK, S. R. 2016).  Researchers began to suspect, due to the fact that the Zika outbreak happened at the same time as the increase in microcephaly cases, that perhaps contracting Zika during pregnancy might be the cause of microcephaly in the fetus. What they don’t know, and may never know, is how many of the babies with microcephaly were exposed to Zika in utero.  This may never be possible to measure, as Zika does not stay in the bloodstream for more than about 12 weeks (FRAMEWORK, S. R. 2016).

In one study out in late February, two pregnant women with fetuses with microcephaly were found to have Zika in their amniotic fluid (Calvet, G. et al, 2016).  The study authors note that while this confirms that Zika can pass through the placenta, it does not actually do anything to prove a relationship between Zika and microcephaly, and that finding this is only two fetuses thus far is actually a very small number. The relationship between fetal microcephaly and the Zika virus remains unclear, and the quality of this evidence is poor.

Regarding the suspected link between Zika infection and microcephaly, it is very important to know that this is a suspected link, not a proven one. In fact, experts from the World Health Organization are being very careful to say that the link between Zika virus and microcephaly is a suspected one, but has not been confirmed in any scientific study.  Microcephaly has historically been known to have multiple non-Zika causes, including Down Syndrome and other genetic disorders, exposure to toxic chemicals, smoking in pregnancy, maternal malnutrition and some severe maternal infections. Further cause for caution in assuming a causative link comes from Colombia, where they have had more than 3,000 cases of Zika but no increase in microcephaly rates.

Here is how I think it makes sense to think about this: There was a Zika outbreak and a large increase in microcephaly cases at the same time.  That is potentially scary, but assuming one causes the other without a clear biological pathway and hard evidence is a recipe for causing potentially unnecessary panic. Studies are being conducted to evaluate whether the link might have to do with other factors instead of, or in addition to Zika infection, such as concurrent infections with other diseases and viruses, poor nutrition, toxin exposure (including exposure to chemicals that kill baby mosquitoes), or other unknown environmental factors.

“Should Expectant Families Worry About Zika in the US?” Probably Not.

Even if it is determined that there is a direct link between Zika infection and microcephaly during pregnancy, does this mean pregnant people should worry about becoming infected?  If they live in the US, probably not. To understand why the risk to Americans is so low, it helps to understand a little about how Zika is spread.  Almost every case of Zika ever recorded was transmitted by the mosquito aedes aegypti, the same mosquito species that transmits dangerous but rare infections like Dengue Fever, Yellow Fever, and Chikungunya, all of which are considered more dangerous than Zika.  The typical American probably has not even heard of these.  The reason that these infections are extremely rare in the US is because the aedes aegypti mosquito is not common here.  While they have been seen in small numbers in the warmer US states such as Texas, Florida, Hawaii and Southern California, the number of outbreaks of these diseases has been very few.  Even more importantly, because of our excellent public health and disease control infrastructure, the occasional outbreak is isolated and eradicated very quickly.  Should an outbreak of Zika suddenly occur in the US, it would also likely be contained and controlled quickly and effectively.

While this does mean that Zika could theoretically spread in this country, I think it is important to use Dengue, Yellow Fever and Chikungunya as a reference point.  While we have seen cases of these diseases in the United States in recent years, our health departments and the CDC do a remarkable job of isolating the cases, eliminating mosquitoes which could spread the disease in the area, and containing any potential outbreak.  In fact, Hawaii saw over 210 cases of Dengue last year and our public health infrastructure has controlled the potential outbreak effectively.  Over the past 15 years, there have been many Dengue outbreaks in Central America, but we’ve never seen more than a few cases in the US because of our great disease eradication infrastructure.  Florida also saw 11 cases of Chikungunya in 2014, and the spread was eliminated by rapid reporting and vector control responses.         

The fact that people don’t sit around fearing infection with Dengue, Yellow Fever, or Chikungunya in the US is a reminder that we need not fear Zika here either.  Instead, I think of the Zika outbreak as very similar to there being an outbreak of either of these diseases in another country: I would not travel there unless I absolutely had to, and I would cover up and use lots of repellent if I did go (more on that below).  What I wouldn’t do is panic (lots more on that below).

Reasonable Steps to Avoid Zika

If a family feels a little concerned about Zika exposure, here or abroad, they could

  • Consider using mosquito repellents that are effective against aedes aegypti. Per the EPA, it is safe to use insect repellents containing DEET, picaridin, and IR3535 in pregnancy.  NPR recently published an article summarizing research on which repellents most effectively keep aedes aegypti away. For complete list of products and their EPA ratings, check out this article.         
  • Cover up or stay inside. The aedes aegypti species typically bites during the day and at dusk.  Because of this, mosquito nets for sleeping aren’t useful.
  • Use air conditioners and window screens to keep mosquitoes out of the home. Sleep in an air-conditioned room (mosquitoes hate cold).
  • Try to eliminate mosquito-breeding grounds near the home.  Mosquitoes breed in standing water, even tiny puddles like the dish under a house plant.  Get rid of this standing water and there will be fewer mosquitoes around, period.
  • Those who are pregnant or considering pregnancy should consider postponing travel to areas with Zika virus transmission.

Further info on avoiding mosquito bites is available at this CDC web page.

If a Pregnant Person Believes They May Have Been Exposed to Zika

  • If someone traveled to any of the affected areas during pregnancy, or do so in the future, they should tell their prenatal provider.  The blood tests for Zika seem only to be accurate within two months of infection, so if it was more than three months ago, guidelines suggest monthly ultrasounds to measure the baby’s head (Peterson, E.E. 2016).  If the baby’s head was already measured at an anatomy scan or another ultrasound, this should be reassuring.  If the test is negative, the CDC still recommends ultrasounds (they are erring on the side of extra surveillance and caution).
  • If someone might have Zika, they should avoid getting more mosquito bites.  This way, they can avoid risk of transmitting Zika within the US.
  • If their partner went to an area with Zika, it seems prudent to avoid unprotected sex for at least two weeks. While the CDC does recommend condoms throughout pregnancy for all those with potentially-exposed partners, there has never been a documented cases of transmission more than a week after exposure.

To Get The Most Up-To-Date Info and Recommendations

Go to the CDC’s most concise and helpful site (and do all you can to avoid media reports): to find out what the current recommendations are and to read the most recent reports and information on this topic.

Come back to Science & Sensibility on Thursday where Rebekah helps put the risk of contracting the Zika virus in perspective with other risks that families face during their pregnancies.  Understanding this risk is critical for families to be able to make decisions during their pregnancies.  Birth professionals will want to be able to discuss this with clients and students.


Calvet, G., Aguiar, R. S., Melo, A. S., Sampaio, S. A., de Filippis, I., Fabri, A., … & Tschoeke, D. A. (2016). Detection and sequencing of Zika virus from amniotic fluid of fetuses with microcephaly in Brazil: a case study. The Lancet Infectious Diseases.

FRAMEWORK, S. R. (2016). ZIKA. (

Petersen, E., Staples, E., Meaney-Delman, D., Fischer, M., Ellington, S., Callaghan, W., & Jamieson, D. (2016). Interim Guidelines for Pregnant Women During a Zika Virus Outbreak – United States, 2016.  Centers for Disease and Control: Morbidity and Mortality Weekly Report (MMWR).

About Rebekah Wheeler

© Rebekah Wheeler

© Rebekah Wheeler

Rebekah Wheeler, RN, CNM, MPH, works as a full-scope Nurse-Midwife in San Francisco.  She moved to the Bay Area in 2011, after completing her MPH and MSN at Yale University.  Before becoming a midwife, she worked in international women’s health programming and research in Tanzania, Malawi, South Africa and Mexico. She is the founder of the Malawi Women’s Health Collective, a small non-profit she created while on a Fulbright scholarship. Rebekah has served on the boards of the California Nurse-Midwifery AssociationPlanned Parenthood of Rhode Island and the Women’s Health and Education Fund of Southeastern Massachusetts.

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