Dear Radhakrishnan,

It seems that pregnant women with the virus may give birth to infants with microcephaly: babies are born with a head circumference below 33 cm and irreversible mental retardation, when they manage to survive.

But health officials also point, each time, as if the existence of that risk seems very likely it does not mean scientifically established. The "causal link" between maternal infection and cranial malformation of the newborn is not indisputably proven. This demonstration will still require different work from sophisticated virological tools. The evidence today are made by this new emerging discipline that is the "spatial and temporal epidemiology"

With my best regards

Prof. Bachir ACHOUR

In short, we don't know yet.

Its a plausible and coherent risk factor (ZV was isolated from aborted fetus with malformations, and placental tissues), but the strength of association is unknow (no case-control study was done), reproductibility was not estabilished, and specificity and temporality are issues (mass vaccination campaings at critical areas to young females and incidence curve of ZV infection did not match pregnancy risk phase on microcephaly cases).  

Vertical transmission of Zika.

There is some evidence of vertical transmission of Zika virus. However not conclusive. WHO stated that research into the etiology of new clusters of microcephaly and other neurological disorders should be intensified to determine whether there is a causative link to Zika virus and/or other factors or co-factors.

According the Pan American Health Organization recent bulletins, in January 2016, the Brazilian Ministry of Health reported the detection of the Zika virus genome by the RT-PCR technique in four cases of congenital malformation in the state of Rio Grande do Norte. The cases correspond to two miscarriages and two full-term newborns (37 and 42 weeks of gestation, respectively) that died within the first 24 hours of life. Immunohistochemistry tests of the tissue specimens from both newborns were also positive for Zika virus.(PAHO 2016)

This evidence complements the finding reported in the epidemiologic alert issued on December 1, 2015, concerning the detection of the Zika virus genome. Using the RT-PCR technique, the genome was detected in the amniotic fluid of two pregnant women in Paraiba, whose fetuses presented microcephaly, as indicated by ultrasonography.

In January, the ICC/Fiocruz laboratory in Parana confirmed the presence of the virus in the placenta of a pregnant woman of the Northeastern region of Brazil, who had a missed abortion in the first trimester of pregnancy.(PAHO 2016)

The World Health Organization panel of experts advising the Director General in International Health Regulation has concluded that After a review of the evidence, the Committee advised that the recent cluster of microcephaly cases and other neurological disorders reported in Brazil, following a similar cluster in French Polynesia in 2014, constitutes an “extraordinary event” and a public health threat to other parts of the world. 

http://www.who.int/mediacentre/news/statements/2016/1st-emergency-committee-zika/en/

I respond to your questions there https://youtu.be/0vyHd4BBRDk

There is some evidence of vertical transmission but no definite association has been proved till yet

Causality is unproven so a lot more epidemiological investigation is required. This recently published research comment may help- Microcephaly in Brazil: how to interpret reported numbers?

Brazilian scientists have identified  microcephaly in babies of infected mothers, howeve

more studies and rigurosity are needed to come to establish a cause effect  relationship, in the mean time as public health measure governments are giving a warning to pregnant women of the potential risk of a Zika infection.