When is Zika Most Harmful to a Fetus?

Abdulla Al-Khan, MD, director of the Division of Maternal-Fetal Medicine and Surgery at Hackensack University Medical Center, explains the threat of Zika, and when it is most harmful to a fetus.

Interview Transcript (slightly modified for readability)

“Zika is a virus which leads to acute viremia and acute viral syndrome. Most individuals tolerate this acute infection relatively well, with minor symptoms no different from [those brought on by] any viral infection—headache, muscle ache, conjunctivitis, a little fever—and they all do extremely well. The biggest problem with Zika is not really infection to the mother, but it is the implication of this virus that affects the embryo.

At what state of embryological development does [a] Zika [infection pose] the highest risk to the fetus? I don’t think anybody really knows, but I think most of the evidence is going towards that this may affect the baby if the mother is exposed to Zika early in the [pregnancy], mostly towards the first an earlier part of the second trimester. I think with Zika people have to understand that our biggest concern is [infection during] pregnancy, and [fetal] exposure to this infection in [women] who are pregnant, especially very early in the pregnancy. And of course [risk of transmitting infection during] the latter part of the pregnancy, end of the second and third trimesters, is always a major question: does Zika lead to severe neurologic insult in a fetus in utero in the third trimester? I don’t think anybody really knows the answer, and this is why we just give the general precautions: avoid Zika-infected areas if possible, if you’re pregnant. So I think it’s important for people to understand that that Zika infection is really a major concern to [women] in the reproductive age group who want to conceive, or especially who do conceive and are exposed, especially very early in the pregnancy.”