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Outcomes of Pregnancies with Laboratory Evidence of Possible Zika Virus Infection in the United States

Outcomes for Completed Pregnancies in the US States and District of Columbia, 2016-2017

Completed pregnancies with or without birth defects

1,471

Includes aggregated data reported to the US Zika Pregnancy Registry*

Liveborn infants with birth defects*

64

Includes aggregated data reported to the US Zika Pregnancy Registry*

Pregnancy losses with birth defects**

8

Includes aggregated data reported to the US Zika Pregnancy Registry*

*As of May 9, 2017

About these numbers

What these numbers show

  • The number of completed pregnancies with or without birth defects include those that ended in a live birth, miscarriage, stillbirth, or termination.
  • The number of liveborn infants and pregnancy losses with birth defects include those among completed pregnancies with laboratory evidence of possible Zika virus infection that have been reported to the US Zika Pregnancy Registry.
  • These numbers rely on reporting to the US Zika Pregnancy Registry and may increase or decrease as new cases are added or information on existing cases is clarified. For example, CDC cannot report the number of completed pregnancies with or without poor pregnancy outcomes that have not yet been reported to the US Zika Pregnancy Registry.
  • The number of liveborn infants and pregnancy losses with birth defects are combined for the 50 US states, and the District of Columbia. CDC is not reporting individual state, tribal, territorial or jurisdictional level data to protect the privacy of the women and children affected by Zika. CDC is using a consistent case inclusion criteria to monitor brain abnormalities and other adverse pregnancy outcomes potentially related to Zika virus infection during pregnancy in the US states and territories. Puerto Rico is not using the same inclusion criteria; CDC is not reporting numbers for adverse pregnancy outcomes in the territories at this time.
  • Birth defects reported include those that have been detected in infants infected with Zika before, during, or shortly after birth, including microcephaly, calcium deposits in the brain indicating possible brain damage, excess fluid in the brain cavities and surrounding the brain, absent or poorly formed brain structures, abnormal eye development, or other problems resulting from damage to brain that affects nerves, muscles and bones, such as clubfoot or inflexible joints, and confirmed hearing loss.

What these new numbers do not show

  • These numbers are not real time estimates. They reflect the outcomes of pregnancies with any laboratory evidence of possible Zika virus infection reported to the US Zika Pregnancy Registry as of 12 noon Tuesday the week prior. Additionally, there may be delays in reporting of pregnancy outcomes from the jurisdictions.
  • Although these outcomes occurred in pregnancies with laboratory evidence of possible Zika virus infection, we do not know whether they were caused by Zika virus infection or other factors.

Where do these numbers come from?

  • These data reflect pregnancies reported to the US Zika Pregnancy Registry. CDC, in collaboration with state, local, tribal and territorial health departments, established this system for comprehensive monitoring of pregnancy and infant outcomes following Zika virus infection.
  • The data collected through this system will be used to update recommendations for clinical care, to plan for services and support for pregnant women and families affected by Zika virus, and to improve prevention of Zika virus infection during pregnancy.

The US Zika Pregnancy Registry and the Puerto Rico Zika Active Pregnancy Surveillance System are covered by an assurance of confidentiality. This protection requires us to safeguard the information collected for the pregnant women and infants in the registries.

Detailed case inclusion criteria for healthcare providers

The following details the inclusion criteria for brain abnormalities and other adverse outcomes potentially related to Zika virus infection during pregnancy. All pregnancy outcomes are monitored, but weekly reporting of adverse outcomes is limited to those meeting the criteria below. All prenatal and postnatal adverse outcomes are reported for both Zika Pregnancy Registries (US Zika Pregnancy Registry, Zika Active Pregnancy Surveillance System) and Active Birth Defects Surveillance; however, case finding methods dictate some differences in specific case definitions.

Brain abnormalities with and without microcephaly

  • Confirmed or possible congenital microcephaly#
  • Intracranial calcifications
  • Cerebral atrophy
  • Abnormal cortical formation (e.g., polymicrogyria, lissencephaly, pachygyria, schizencephaly, gray matter heterotopia)
  • Corpus callosum abnormalities
  • Cerebellar abnormalities
  • Porencephaly
  • Hydranencephaly
  • Ventriculomegaly / hydrocephaly (excluding “mild” ventriculomegaly without other brain abnormalities)
  • Fetal brain disruption sequence (collapsed skull, overlapping sutures, prominent occipital bone, scalp rugae)
  • Other major brain abnormalities, including intraventricular hemorrhage in utero (excluding post-natal IVH)

Neural tube defects and other early brain malformations

  • Neural tube defects (NTD)
    • Anencephaly / Acrania
    • Encephalocele
    • Spina bifida
  • Holoprosencephaly / Arhinencephaly

Structural eye abnormalities

  • Microphthalmia / Anophthalmia
  • Coloboma
  • Cataract
  • Intraocular calcifications
  • Chorioretinal anomalies involving the macula (e.g., chorioretinal atrophy and scarring, macular pallor, gross pigmentary mottling and retinal hemorrhage); excluding retinopathy of prematurity
  • Optic nerve atrophy, pallor, and other optic nerve abnormalities

Consequences of central nervous system (CNS) dysfunction

  • Congenital contractures (e.g., arthrogryposis, club foot, congenital hip dysplasia) with associated brain abnormalities
  • Congenital deafness documented by postnatal testing

#Live births: measured head circumference (HC) adjusted for gestational age and sex <3rd percentile at birth, or if not measured at birth, within first 2 weeks of life; pregnancy loss: prenatal HC* more than 3 SD below the mean based on ultrasound or postnatal HC <3rd percentile. Birth measurements based on intergrowth21 standards which are based on measurements within 24 hours of birth, and therefore measurements within 24 hours of birth are appropriate for this assessment.

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