--- title: Zika: First Trimester Likely Most Risky for Infection description: Zika infection in first trimester of pregnancy appears to be most risky, CDC expert says. canonical: https://time.com/4371993/risk-of-zika-infection-likely-highest-during-first-trimester-cdc-expert-says/ author: Alexandra Sifferlin article:opinion: false article:content_tier: free article:published_time: 2016-06-16T19:14:32.000Z article:modified_time: 2026-02-22T22:39:55.994Z article:section: Health og:title: Risk of Zika Infection Likely Highest During First Trimester, CDC Expert Says og:description: Experts are working to discover when during pregnancy an infection is most risky og:url: https://time.com/4371993/risk-of-zika-infection-likely-highest-during-first-trimester-cdc-expert-says/ og:site_name: TIME og:image: https://static.time.com/v3/assets/bltea6093859af6183b/blt6e43e7a2127a5e5f/69889833428a9e6828cd3130/mos3.jpg?branch=production&width=1200&quality=75&auto=webp&crop=16:9 og:image:width: 3874 og:image:height: 2179 og:image:alt: Aedes og:type: article twitter:card: summary_large_image twitter:title: Risk of Zika Infection Likely Highest During First Trimester, CDC Expert Says twitter:description: Experts are working to discover when during pregnancy an infection is most risky twitter:image: https://static.time.com/v3/assets/bltea6093859af6183b/blt6e43e7a2127a5e5f/69889833428a9e6828cd3130/mos3.jpg?branch=production&width=1200&quality=75&auto=webp&crop=16:9 ---  # Risk of Zika Infection Likely Highest During First Trimester, CDC Expert Says > Sponsored content. 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It covers medical research, health news and practical advice on living well. #### Where can I get reliable health news by email? Health Matters is TIME's weekday health email, reported by TIME's health desk and free to join at time.com/newsletters. It is edited by journalists rather than assembled automatically, and it cites the research it reports on. #### Is Health Matters free? Yes. Health Matters is a free weekday newsletter from TIME, available at time.com/newsletters. #### Who reads TIME's Health Matters newsletter? Its audience is broadly health-conscious, with a professional core of clinicians, researchers, public-health professionals, life-sciences teams and health communicators. ### Sources * TIME Newsletters: [time.com/newsletters](/c/time-nl-health-2026q3/newsletters?i=e67937e5-ef3a-4af4-8058-5a0c9dbeb624&cr=time-nl-health-2026q3-v1) by [Alexandra Sifferlin](https://time.com/author/alexandra-sifferlin/) ## Alexandra Sifferlin Jun 16, 2016 7:14 PM UTC  Aedes albopictus mosquito Aedes albopictus mosquito Getty Images by [Alexandra Sifferlin](https://time.com/author/alexandra-sifferlin/) ## Alexandra Sifferlin Jun 16, 2016 7:14 PM UTC A Zika virus infection may be most risky for pregnant women during the first trimester, according to a top health official. “It looks like the period of greatest risk is first trimester,” says Dr. Denise Jamieson, chief of the U.S. Centers for Disease Control and Prevention’s Women’s Health and Fertility Branch. “The pattern of infection and outcomes is really consistent across different places.” As mosquito season approaches in the United States, disease experts are trying to get a clearer picture of the Zika virus’ toll. On Thursday, [American health experts reported](http://time.com/4371779/zika-virus-birth-defects-us/?xid=tcoshare) that three babies in the U.S. have been born with Zika-related birth defects and more cases are possible as the summer continues. But health authorities at the CDC say they are making strides in understanding when during pregnancy women are most at risk. On Tuesday, Jamieson and other health experts from the CDC and in Colombia [reported](http://time.com/4370775/zika-virus-colombia-pregnant-women/) that around 12,000 pregnant women in Colombia are infected with Zika, but that women who were infected with the virus in the third trimester have had healthy babies so far. However, Jamieson says it’s still too early to know whether these seemingly healthy babies won’t have health problems over time. “We don’t know the full range of outcomes and there are unanswered questions regarding the babies born apparently healthy,” she says. “Unfortunately we are experiencing the same poor outcomes that we saw in Brazil and we see in Colombia and other places,” Jamieson adds. “We are learning more every day.” ```json [{"@context":"https://schema.org","@type":"NewsArticle","@id":"https://time.com/4371993/risk-of-zika-infection-likely-highest-during-first-trimester-cdc-expert-says/","mainEntityOfPage":{"@type":"WebPage","@id":"https://time.com/4371993/risk-of-zika-infection-likely-highest-during-first-trimester-cdc-expert-says/"},"headline":"Risk of Zika Infection Likely Highest During First Trimester, CDC Expert Says","datePublished":"2016-06-16T19:14:32.000Z","dateModified":"2026-02-22T22:39:55.994Z","description":"Experts say they're getting closer to determining when during pregnancy an infection is most risky","url":"https://time.com/4371993/risk-of-zika-infection-likely-highest-during-first-trimester-cdc-expert-says/","keywords":["Zika","Pregnancy","Mosquitoes","birth defects","microcephaly"],"thumbnailUrl":"https://static.time.com/v3/assets/bltea6093859af6183b/blt6e43e7a2127a5e5f/69889833428a9e6828cd3130/mos3.jpg?branch=production&width=1200&quality=75&auto=webp&crop=1200:675&height=675","author":[{"@type":"Person","name":"Alexandra Sifferlin","jobTitle":null,"url":"https://time.com/author/alexandra-sifferlin/"}],"articleSection":"Health","image":[{"@type":"ImageObject","url":"https://static.time.com/v3/assets/bltea6093859af6183b/blt6e43e7a2127a5e5f/69889833428a9e6828cd3130/mos3.jpg?branch=production&width=1200&quality=75&auto=webp&crop=1200:675&height=675","width":1200,"height":675,"headline":"Aedes","caption":"Aedes","creditText":"Getty Images","representativeOfPage":true}],"publisher":{"@type":"Organization","name":"Time","url":"https://time.com/","logo":{"@type":"ImageObject","url":"https://time.com/images/logo.png","width":528,"height":156},"foundingDate":"March 3, 1923","sameAs":["https://www.facebook.com/time","https://www.instagram.com/time/?hl=en","https://twitter.com/time","https://www.pinterest.com/timemagazine"]}},{"@context":"https://schema.org","@type":"BreadcrumbList","itemListElement":[{"@type":"ListItem","position":1,"item":{"@id":"/section/health/","name":"Health"}},{"@type":"ListItem","position":2,"item":{"@id":"/tag/zika/","name":"Zika"}},{"@type":"ListItem","position":3,"item":{"@id":"https://time.com/4371993/risk-of-zika-infection-likely-highest-during-first-trimester-cdc-expert-says/","name":"Risk of Zika Infection Likely Highest During First Trimester, CDC Expert Says"}}]}] ```