A clearer picture of the risk Zika poses for pregnant women is emerging with more publication of studies following women who were infected. While the evidence is stronger than ever that some Zika-infected pregnant women’s babies will develop problems, not all pregnant women who become sick from Zika virus will have a pregnancy complication or a baby with birth defects.{{more}}

In microcephaly, a baby’s much smaller-than-average head size is accompanied by a smaller brain and developmental difficulties. Several papers have come out clearly showing the structural changes in the brain, and now a very plausible mechanism for this occurrence.

The largest of these studies followed 88 pregnant women from Rio de Janeiro, Brazil, between September 2015 and February 2016, starting within five days after they each developed a rash. A rash is one of the most common symptoms of Zika infection, along with fever, joint pain, and red or itchy eyes. Of the 88 women, 72 tested positive for Zika according to the study, which was published March, 2016 in the New England Journal of Medicine (NEJM).

Studies have also shown that late pregnancy loss can also occur due from Zika infection. In a case study published in February 2016 in the journal PLOS Neglected Tropic Diseases, researchers described the case of a 20-year-old woman whose fetus showed severely slowed growth in week 18 of pregnancy. The woman did not remember having had symptoms of a Zika infection, however. Additional ultrasounds later in the pregnancy showed problems similar to those seen in the Brazilian women in the first study, as well as an abnormal build-up of fluid inside the fetus’s body. The fetus died at 32 weeks of pregnancy.

Another study, reported by Dana Meaney-Delman, MD, and other scientists at the Centers for Disease Control and Prevention (CDC), followed nine pregnant women in the United States who had travelled to countries where Zika was circulating. Up until February 17, 2016, these women, and 10 others under observation, were the only pregnant women in the United States with confirmed Zika infections.

Two of the women had miscarriages in the first trimester, and two chose to have abortions after ultrasounds revealed severe defects in the fetuses’ brains. One woman gave birth to a baby with microcephaly, two women gave birth to healthy babies, and the other two women’s pregnancies continued without any current problems. Several of the women who lost their fetuses or had fetuses with defects showed Zika infection.

The best way to reduce risk of infection is to prevent mosquito bites. Stay inside homes and buildings with air-conditioning, keep windows closed, and use mosquito repellents. In addition, you can prevent getting Zika through sex by using condoms if your male partner has been to an area that has the Zika virus.

If you’re pregnant and do travel to or return from these areas with Zika symptoms – a rash with fever, red or itchy eyes, and joint pain or a headache – you should contact your health care provider or local health department. Women who test positive should have regular ultrasounds to look for problems.

Remember many pregnant women become infected with Zika and give birth to healthy babies.

Dr Rosmond Adams, MD is a medical doctor and a public health specialist with training in bioethics and ethical issues in medicine, the life sciences and research. He is the head of Health Information, Communicable Diseases and Emergency Response at the Caribbean Public Health Agency (CARPHA). (The views expressed here are not written on behalf of CARPHA).

Dr Rosmond Adams is a medical doctor and a public health specialist.