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CDC Provides Updates on Zika-Related Birth Defects

MAY 13, 2016 | SARAH ANWAR
In response to the impending threat of active Zika transmission in the Continental US and Hawaii, the CDC is:
  • Increasing lab capacity for testing to identify Zika virus infection
  • Assisting in development of Zika detection tests
  • Collaborating with partners to control vector populations
  • Providing infection prevention recommendations
  • Building state capacity to identify babies with Zika-related birth defects
Janet Cragan, MD, MPH, medical officer in the CDC’s National Center on Birth Defects and Developmental Disabilities, delved into the details of microcephaly. She noted that there is currently no single accepted definition of the abnormality, since clinicians are using different cut-off points for diagnosis: head circumference less than third, fifth, or tenth percentile in comparison to infants of the same age and sex. However, during the teleconference, the CDC provided the listeners with a “Zika-related definition of congenital microcephaly,” which is divided into two parts, definite and possible:
  • Definite
    • Live births
      • Head circumference (HC) at birth <3rd percentile for gestational age and sex, OR
      • If HC at birth is not available, HC <3rd percentile for age and sex within the first 6 weeks of life, adjusted for gestational age if preterm
    • Stillbirths and Elective Terminations
      • HC at delivery <3rd percentile for gestational age and sex
  • Possible
    • Live births
      • If an earlier HC is not available, HC <3rd percentile for age and sex beyond 6 weeks of life
    • All Pregnancy Outcomes
      • Microcephaly diagnosed or suspected on prenatal ultrasound in the absence of available postnatal HC measurements
Dr. Cragan also identified three distinct types of microcephaly:
  • Disproportionate- the infant’s head is disproportionate to the weight and length, but is normal for its age and sex
  • Proportionate- the infant’s head, weight, and length are too small for its age and sex, but are in proportion to each other
  • Relative microcephaly- the infant’s head size is within normal range for its age and sex, but is disproportional to its weight and length.
It was noted that infants born with microcephaly can expect a lifetime of cognitive and neurological impairments.

Dr. Cragan also discussed the importance of monitoring the prevalence of microcephaly. The CDC suggests that cases be divided by severity, known cause, and unknown cause. Suggested sources for data collection included areas where births and elective terminations occur (including home births), and hospitals and clinics where these infants are treated; the importance of reporting details specific to each case (in terms of the observed abnormalities) was also stressed.

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