Clinical Considerations for Pregnant Persons with Possible Zika Virus Infection

Fetal ultrasound

For pregnant people with confirmed or possible Zika virus infection, serial fetal ultrasounds (every 3–4 weeks) should be considered. This is to assess fetal anatomy, particularly fetal neuroanatomy, and to monitor growth closely. Prenatal ultrasounds should include a detailed fetal anatomy to detect brain or associated structural abnormalities that might occur before microcephaly. For updated clinical management recommendations during pregnancy, refer to CDC's updated interim guidance.

Insufficient data are available to define the optimal timing between Zika virus exposure and initial sonographic screening. Abnormalities have been detected anywhere from 2 to 29 weeks after symptom onset. Brain abnormalities have been identified by ultrasound in the second and third trimesters in case reports.

In the absence of data to guide timing of ultrasound, healthcare providers may consider extending the time interval between ultrasounds in accordance with patient preferences and clinical judgement.

Accuracy

The accuracy of ultrasound to detect brain abnormalities in the setting of Zika virus infection during pregnancy is not known. It will depend on many factors, such as

• timing of gestational parent infection relative to timing of screening,
• severity of the abnormality,
• patient factors (e.g., obesity),
• gestational age,
• equipment used, and
• the expertise of the person performing the ultrasound.

Sensitivity

The sensitivity of prenatal ultrasound for detection of microcephaly and brain abnormalities depends on a range of factors. These can include timing of screening, severity of microcephaly, and patient factors. In a study of congenital microcephaly not caused by Zika virus infection, prenatally diagnosed microcephaly correlated with neonatal microcephaly approximately 57% of the time. Limited data suggest that a constellation of ultrasound abnormalities (e.g., microcephaly, ventriculomegaly, or abnormalities of the corpus callosum) identified prenatally in the context of Zika virus exposure during pregnancy correlate with reported structural abnormalities in infants at birth.

Fetal MRI

Fetal MRI is not a screening tool. It 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.

Amniocentesis

The role of amniocentesis for the detection of congenital Zika virus infection is unknown. Consideration of amniocentesis should be individualized based on the patient's clinical circumstance. Amniocentesis has been used in the evaluation of other congenital infections and may be considered in the evaluation of potential Zika virus infection. Healthcare providers should discuss the risks and benefits of amniocentesis with their patients.

Amniocentesis is not recommended until after 15 weeks of gestation. Amniocentesis performed at ≥15 weeks of gestation is associated with lower rates of complications than when performed at earlier gestational ages. However, the optimal time to perform amniocentesis to diagnose congenital Zika virus infection is not known. Referral to a maternal-fetal medicine specialist may be warranted.

A positive Zika virus nucleic acid amplification tests (NAAT) result from amniotic fluid might indicate fetal infection. This information would be useful for pregnant people and their healthcare providers to assist in determining clinical management (e.g., antepartum testing, scheduling serial ultrasounds, delivery planning). Reports of the correlation between positive Zika test results in amniotic fluid and clinical phenotype or confirmatory infant laboratory testing are inconsistent. Zika virus RNA has been detected in amniotic fluid specimens; however, serial amniocenteses have demonstrated that Zika virus RNA might only be present transiently.

Although a negative Zika virus NAAT result from amniotic fluid does not exclude congenital Zika virus infection, it may prompt a further evaluation for other causes of microcephaly (e.g., other infections, genetic disorders).

We do not know for Zika virus infections in pregnancy and amniocentesis:

• The optimal time to perform amniocentesis.
• How sensitive or specific tests of amniotic fluid are.
• If a positive result is predictive of fetal abnormality.