The birth rate in Brazil in 2015 was 14.46 births&#x2F;1,000 population[1].  The twin rate is 8.8&#x2F;1,000 births[2]. So, of 1,000,000 who got sick, roughly 14,300 were pregnant women[3], resulting in a 28% chance of microcephaly.<p>That still comes with a big asterisk since 80% cases of the disease in the general population are asymptomatic[4].  But(!) pregnant women are at increased risk for many diseases.<p>[1] <a href="https:&#x2F;&#x2F;www.cia.gov&#x2F;library&#x2F;publications&#x2F;the-world-factbook&#x2F;geos&#x2F;br.html" rel="nofollow">https:&#x2F;&#x2F;www.cia.gov&#x2F;library&#x2F;publications&#x2F;the-world-factbook&#x2F;...</a><p>[2] <a href="http:&#x2F;&#x2F;journals.plos.org&#x2F;plosone&#x2F;article?id=10.1371&#x2F;journal.pone.0025239#s5" rel="nofollow">http:&#x2F;&#x2F;journals.plos.org&#x2F;plosone&#x2F;article?id=10.1371&#x2F;journal....</a><p>[3] who carried to term<p>[4] <a href="https:&#x2F;&#x2F;www.washingtonpost.com&#x2F;world&#x2F;the_americas&#x2F;brazilians-panic-as-mosquito-linked-to-brain-damage-in-thousands-of-babies&#x2F;2016&#x2F;01&#x2F;15&#x2F;7e8e2dec-b8ca-11e5-85cd-5ad59bc19432_story.html" rel="nofollow">https:&#x2F;&#x2F;www.washingtonpost.com&#x2F;world&#x2F;the_americas&#x2F;brazilians...</a>