Technical and Clinical Information on Zika and Pregnancy

Healthcare providers and health departments can use these resources to help collect information for the Registry. These technical details help ensure that data are collected in a consistent way.

Reporting to the Registry

Healthcare providers should report information on eligible pregnant women and infants to their state, local, tribal, or territorial health departments. Eligible pregnant women and infants include those that meet Registry criteria and have completed their pregnancies from December 1, 2015 to March 31, 2018. Pregnancies with possible Zika virus infection that are ongoing after March 31, 2018, will not be included in the reported numbers. However, state, tribal, local, and territorial health departments may continue to securely send medical information to CDC Registry staff.

Health department staff can submit information to CDC staff by

  • CDC Secure Access Management Services (SAMS)
  • Electronic data transfer through FTP (e.g. CSV, Excel, Access, Word, PDF files)
Doctor and nurse doing checkup on little boy

Gestational Age and Trimesters

The estimated date of delivery (EDD) is a key piece of information for the US Zika Pregnancy and Infant Registry. For a given pregnancy there should be one EDD established early in pregnancy, based either by ultrasound measurements or on the first day of the last menstrual period (LMP). EDD estimates are generally determined early in pregnancy and may be confirmed by ultrasound. Ultrasounds early in pregnancy are more accurate to confirm EDD than those later in pregnancy. When questions arise about the most accurate EDD, CDC will work with the health department and/or clinician to determine the most accurate EDD for the Registry. It is important to include how EDD was established because this information assists in determining exposure timing and gestational age.

The Registry defines pregnancy trimesters using the American Congress of Obstetricians and Gynecologists definitions:

  • First Trimester: Begins 2 weeks after the last menstrual period (2 weeks gestation) and extends until 13 weeks plus 6 days
  • Second Trimester: Begins at 14 weeks gestation and extends until 27 weeks and 6 days
  • Third Trimester: Begins at 28 weeks gestation and extends until delivery

Conventions for gestational notation are based on the 7-day week.

Laboratory Evidence of Possible Zika Virus Infection

The following explains the US Zika Pregnancy and Infant Registry inclusion criteria for laboratory evidence of Zika virus infection.

  • Recent Zika virus infection detected by Zika RNA nucleic acid test (NAT) (e.g., real-time reverse transcription polymerase chain reaction [rRT-PCR]):
    • Zika virus RNA detected by NAT on any maternal or fetal/infant clinical specimen (e.g., serum, urine, whole blood, cerebrospinal fluid, amniotic fluid, cord blood, saliva, placenta, umbilical cord tissue, placental membranes, or fetal tissue)
  • Recent Zika virus infection or recent flavivirus infection detected by serologic tests of maternal or infant serum or cerebrospinal fluid
    • Zika virus IgM positive or equivocal AND Zika virus plaque reduction neutralization test (PRNT) titer ≥10, (regardless of dengue virus PRNT value) OR
    • Zika virus IgM positive or equivocal AND Zika virus PRNT not performed in following state, tribal, local, or territorial health department protocol, OR
    • Zika virus IgM negative AND dengue virus IgM positive or equivocal AND Zika virus PRNT titer ≥10 (regardless of dengue virus PRNT titer)
    • These inclusion criteria are intentionally broad because of the known cross-reactivity in IgM testing and inability to distinguish between Zika and dengue virus through the use of PRNT.
    • If maternal Zika virus IgM and dengue virus IgM are both negative, and maternal PRNT was performed per jurisdictional protocol with Zika virus PRNT titer ≥10, additional testing is needed to meet inclusion criteria. For example, if maternal testing is performed >12 weeks from possible Zika virus exposure and maternal IgM testing is negative with Zika virus PRNT titer ≥10, the mother-infant pair would be included if the infant had Zika virus IgM positive or equivocal, Zika virus RNA or antigen detected, or Zika virus cultured.
  • Zika virus infection confirmed by other tests in any maternal or fetal/infant clinical specimen (e.g., serum, urine, whole blood, cerebrospinal fluid, amniotic fluid, cord blood, saliva, placenta, umbilical cord tissue, placental membranes, or fetal tissue)
    • Culture of Zika virus
    • Detection of Zika virus antigen
Doctor taking to pregnant woman

CDC Standard Case Definition for Healthcare Providers

CDC uses a standard case definition for birth defects potentially associated with Zika virus infection. This case definition is used for both the US Zika Pregnancy and Infant Registry as well as Zika Birth Defects Surveillance. This standard case definition helps CDC determine the total pregnancies with possible Zika virus infection and adverse outcomes potentially related to Zika in the United States. These numbers include brain abnormalities and other birth defects potentially related to Zika virus infection during pregnancy. All pregnancy outcomes are monitored, but reporting of birth defects is limited to those meeting the following criteria.

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
Neural tube defects and other early brain malformations§
Structural eye abnormalities
  • Anophthalmia/ Microphthalmia
  • 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

*For more information on the clinical guidance for head circumference measurements, see the Congenital Zika Syndrome webpage

§Neural tube defects and other early brain malformations are included as biologically plausible birth defects; however, they have been reported much less frequently with Zika virus infection than defects in the other categories.