Zika and Pregnancy
What is known about the effects of Zika virus on pregnant women?
We expect that the course of Zika virus disease is similar to that in the general population. No evidence exists to suggest that pregnant women are more susceptible or experience more severe disease during pregnancy. It is not known if pregnant women are more susceptible to Guillain-Barré syndrome.
Is there any association between Zika virus infection and congenital microcephaly?
There have been reports of congenital microcephaly in babies of mothers who were infected with Zika virus while pregnant. Zika virus infections have been confirmed in several infants with microcephaly; it is not known how many of the microcephaly cases are associated with Zika virus infection. Studies are under way to investigate the association of Zika virus infection and microcephaly, including the role of other contributory factors (e.g., prior or concurrent infection with other organisms, nutrition, and environment).
Is there any known association between maternal Zika virus infection and other adverse pregnancy outcomes?
The full spectrum outcomes that might be associated with Zika virus infections during pregnancy is unknown and requires further investigation.
How should pregnant patients who are considering travel to an area with Zika virus transmission be counseled?
CDC recommends that pregnant women in any trimester should consider postponing travel to an area where Zika virus transmission is ongoing. If a pregnant women is considering travel to one of these areas, she should talk to her healthcare provider. If she travels, she should strictly follow steps to avoid mosquito bites during the trip.
How should women trying to become pregnant who are considering travel to an area with Zika virus transmission be counseled?
They should consult with their healthcare provider before traveling to these areas and strictly follow steps to prevent mosquito bites during the trip.
Which pregnant women should be tested for Zika virus infection?
Obstetrical providers should obtain a travel history from all pregnant women and use recent travel history to guide decisions about testing. Testing is not indicated for pregnant women without a travel history to an area with Zika virus transmission.
Pregnant women with a history of travel to an area with Zika virus transmission and who report two or more symptoms consistent with Zika virus disease (including acute onset of fever, maculopapular rash, arthralgia or conjunctivitis) during or within two weeks of travel should be tested. In addition, pregnant women with a history of travel to an area with Zika virus transmission and who have ultrasound findings of fetal microcephaly or intracranial calcifications should also be tested for Zika virus infection. Testing should be performed in consultation with state or local health departments.
CDC travel notices
MMWR Clinical Guidance for Obstetrical Provider
What specimens can be tested for Zika virus?
Zika virus RT-PCR and serology assays can be performed on maternal serum or plasma. Zika virus RT-PCR can also be performed on amniotic fluid. Other testing that can performed includes the following: 1) histopathologic examination and immunohistochemical staining of the placenta and umbilical cord, 2) Zika virus testing of frozen placental tissue and cord tissue, and 3) IgM and neutralizing antibody testing of cord blood.
Who should be offered amniocentesis?
Amniocentesis should be offered to pregnant women with recent travel to an area with Zika virus transmission, reporting2 or more symptoms within two weeks of travel and a positive or inconclusive maternal serum test. For pregnant women with recent travel to an area with Zika virus transmission and ultrasound findings of microcephaly or intracranial calcifications, amniocentesis may also be considered. Consultation with a maternal-fetal medicine specialist should be considered.
Why is amniocentesis offered?
While amniocentesis is a relatively safe test, risk and benefits of amniocentesis should always be considered. An amniocentesis can be used to provide additional clinical information. For example, a positive RT-PCR result on amniotic fluid would be suggestive of intrauterine infection and potentially useful to pregnant women and their healthcare providers to guide decisions about timing of delivery and the level of neonatal care at delivery sites.
When should amniocentesis be performed?
Timing of amniocentesis should be individualized based on the patient’s clinical circumstances. Amniocentesis is not recommended until after 15 weeks of gestation. Amniocentesis performed ≥15 weeks of gestation is associated with lower rates of complications than those performed at earlier gestational ages (≤14 weeks of gestation). However, the exact timing of amniocentesis should be individualized based on the patient’s clinical circumstances. Referral to maternal-fetal medicine or infectious disease specialist with expertise in pregnancy management may be warranted. Risk and benefits of performing the amniocentesis should be discussed with the patient.
How would results of Zika virus RT-PCR amniotic fluid test results inform clinical management of pregnant women?
A positive Zika virus RT-PCR result from amniotic fluid would be suggestive of intrauterine infection. This information would be useful for pregnant women and their healthcare providers to assist in determining clinical management (e.g., antepartum testing, delivery planning). A negative Zika virus RT-PCR result from amniotic fluid may prompt a work up for other causes of microcephaly (e.g., other infections, genetic disorders).
Prenatal Diagnosis of Microcephaly
Why is fetal ultrasound recommended?
Fetal ultrasound is generally performed in pregnancies between 18-20 weeks of gestation to assess fetal anatomy as part of routine obstetrical care. Although microcephaly and intracranial calcifications are typically detected during ultrasounds later in pregnancy, these findings might be detected as early as 18-20 weeks gestation. Microcephaly and intracranial abnormalities have been demonstrated in pregnancies with known Zika virus disease. Hence, additional ultrasounds might provide an opportunity to identify findings consistent with fetal Zika virus infection and offer pregnant women the option of amniocentesis to test for Zika virus RNA.
Is ultrasound safe in pregnancy?
Ultrasound is performed during pregnancy when medical information is needed. It has been used during pregnancy for many years and has not been associated with adverse maternal, fetal, or neonatal outcomes. Ultrasound operators are trained to use the lowest power for the minimum duration of time to obtain the needed information. There is consensus among various national and international medical organizations (American College of Radiology, American College of Obstetricians and Gynecologists, and the Society of Maternal and Fetal Medicine) that ultrasound is safe for the fetus when used appropriately.
What prenatal ultrasound findings have been observed among infants with confirmed Zika virus infection?
Brain abnormalities reported in infants with laboratory-confirmed congenital Zika infection include microcephaly and disrupted brain growth. Some infants with possible Zika virus infection have been found to have intracranial calcifications and abnormal eye findings. It is not known if Zika virus infection caused any of these abnormalities.
In one report of two infants with Zika virus RNA detected by PT-PCR, brain anomalies detected on ultrasound included corpus callosal and vermian dysgenesis, enlarged cisterna magna, severe unilateral ventriculomegaly, agenesis of the thalami, cataracts, intracranial and intraocular calcifications.6
How is microcephaly diagnosed prenatally?
Microcephaly can be diagnosed during pregnancy with ultrasound. Microcephaly is most easily diagnosed by ultrasound late in the 2nd trimester or early in the third trimester of pregnancy.
How early can microcephaly be diagnosed during pregnancy?
Microcephaly might be detected as early as 18-20 weeks of gestation however, detection by prenatal ultrasound can be challenging at this gestational age due to fetal position and fetal motion artifact. The optimal time to perform ultrasound screening for fetal microcephaly is not known. In the absence of microcephaly, the presence of intracranial calcifications before 22 weeks gestation might suggest a risk for the future development of microcephaly.
How accurately can ultrasound detect microcephaly with maternal Zika virus?
The accuracy of ultrasound to detect microcephaly in the setting of maternal Zika virus is not known and will depend on many factors such as the timing of maternal infection relative to the timing of screening, severity of microcephaly, patient factors (e.g., obesity), gestational age, the equipment used, and the expertise of the person performing the ultrasound. Because the absence of fetal microcephaly and intracranial calcifications on ultrasound at one point in pregnancy does not exclude future microcephaly, serial ultrasounds may be considered. As we get more information specifically related to Zika virus infection and microcephaly, we expect that more specific guidance for women and their healthcare providers will be developed.
If a prenatal ultrasound demonstrates microcephaly, how well does it predict microcephaly in the infant?
The sensitivity of prenatal ultrasound for detection of microcephaly depends on a range of factors (e.g., timing of screening, severity of microcephaly, patient factors). In a study of microcephaly not caused by Zika virus infection, prenatally diagnosed microcephaly correlated with neonatal microcephaly approximately 57% of the time.
Can fetal MRI be used to detect microcephaly?
Fetal MRI is not a screening tool and should be used only to answer specific questions raised by ultrasound or used in occasional specific high-risk situations. Interpretation of fetal MRI requires specialized expertise and has limited availability in the United States.