While the link between maternal Zika virus infection and an increase in congenital defects - such as microcephaly - is pretty well accepted, unknown at this time is just how big a risk that really is.
We've only seen two studies on point, and they provided two very different results.
- In Association between Zika virus and microcephaly in French Polynesia, 2013–15: a retrospective study, researchers came up with about a 1% likelihood of microcephalic birth when the mother is infected in the first trimester.
- While in NEJM: Zika Virus Infection In Pregnant Women - Brazil (Preliminary Report), a small study suggested that 29% of women who tested positive for the Zika virus during pregnancy saw `. . . grave outcomes, including fetal death, placental insufficiency, fetal growth restriction, and CNS injury.'
Today the NEJM carries a perspective - based on an analysis of Zika outbreaks in Bahia, Brazil - that attempts to quantify the risks based on the limited information available.
But based on what they know right now, these researchers found a `strong association between the risk of microcephaly and infection risk in the first trimester and a negligible association in the second and third trimesters'.
Then, depending upon which set of assumptions they used (to fill in the missing data gaps) - they came up with a range of risk that ran between .88% and 13.2% - of 1st trimester Zika infection resulting in a microcephalic birth.
Since there are still major gaps in the data, and microcephaly is but one possible `grave outcome', these results need to be taken in context.
Follow the link to read the full report:
Zika and the Risk of Microcephaly
May 25, 2016DOI: 10.1056/NEJMp1605367