--- 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: 2026-10-06T09:28:41.316Z 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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Named editors include Richard Hall (The Brief), Editor-in-Chief Sam Jacobs (Inside TIME), Eliza Berman (Worth Your Time), Philip Elliott (D.C. Brief), Justin Worland (Future Proof) and Harry Booth (In the Loop). Health Matters is written by TIME's health desk. #### How do I sign up for a TIME newsletter? Go to time.com/newsletters, choose the newsletters you want and enter your email address. There is no cost and no subscription requirement. ### Sources * TIME Newsletters: [time.com/newsletters](/c/time-nl-network-2026q3/newsletters?i=23e5d0a7-fae1-49f8-ba3a-29a79e392cf9&cr=time-nl-network-2026q3-v1) ## Video: 12,000 Pregnant Women in Colombia Have Zika [Watch (HLS stream): 12,000 Pregnant Women in Colombia Have Zika](https://cdn.jwplayer.com/manifests/SRAOnkbs.m3u8) (0:49)  _Published 2016-06-16. An early report on Zika spread in Colombia reveals that close to 12,000 pregnant women have the virus._ by [Alexandra Sifferlin](https://time.com/author/alexandra-sifferlin/) ## Alexandra Sifferlin Jun 16, 2016 7:14 PM UTC An early report on Zika spread in Colombia reveals that close to 12,000 pregnant women have the virus. 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.” ## Transcript [00:00] [ MUSIC ] As of April, there were nearly 66, 000 [00:00] reported Zika cases in Colombia, [00:13] but that [00:29] number is likely [00:44] an underestimate. ```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":"2026-10-06T09:28:41.316Z","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":"https://time.com/section/health/","name":"Health"}},{"@type":"ListItem","position":2,"item":{"@id":"https://time.com/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"}}]},{"@context":"https://schema.org","@type":"VideoObject","name":"12,000 Pregnant Women in Colombia Have Zika","description":"An early report on Zika spread in Colombia reveals that close to 12,000 pregnant women have the virus.","thumbnailUrl":"https://cdn.jwplayer.com/v2/media/SRAOnkbs/poster.jpg?width=720","uploadDate":"2016-06-16T14:36:35.000Z","contentUrl":"https://cdn.jwplayer.com/manifests/SRAOnkbs.m3u8","embedUrl":"https://time.com/4371993/risk-of-zika-infection-likely-highest-during-first-trimester-cdc-expert-says/","duration":"PT49S","potentialAction":{"@type":"SeekToAction","target":"https://time.com/4371993/risk-of-zika-infection-likely-highest-during-first-trimester-cdc-expert-says/?jw_start={seek_to_second_number}","startOffset-input":"required name=seek_to_second_number"}}] ```