Skip directly to search Skip directly to A to Z list Skip directly to navigation Skip directly to page options Skip directly to site content

Congenital Microcephaly Case Definitions

Pregnancy Outcomes and Microcephaly Diagnosis

Diagnosing Microcephaly Pregnancy Outcome
Definite Congenital Microcephaly

For Live Births: Head circumference (HC) at birth less than the 3rd percentile for gestational age and sex OR if HC at birth is not available, HC less than the 3rd percentile for age and sex within the first 2 weeks of life

For Stillbirths and Elective Terminations: HC at delivery less than the 3rd percentile for gestational age and sex

Possible Congenital Microcephaly

For Live Births: If earlier HC is not available, HC less than the 3rd percentile for age and sex beyond 6 weeks of life

For All Pregnancy Outcomes: Microcephaly diagnosed or suspected on prenatal ultrasound in the absence of available postnatal HC measurements

Charts for Head Circumference at Birth

Gestational Age Reference Chart for Head Circumference at Birth
33–43 Weeks

INTERGROWTH-21st Newborn Size at Birth Chart and tool for calculating centiles for head circumference for infants 33–42 weeks

24–32 Weeks INTERGROWTH-21st Very Preterm Size at Birth References and tool for calculating centiles for head circumference for infants 24–32 weeks
<24 Weeks INTERGROWTH-21st Fetal Growth Standards

INTERGROWTH-21st Fetal Growth Standards are based on measurements in utero only. International standards for birth measurements in infants less than 24 weeks gestation are not available. For most elective pregnancy terminations and many stillbirths, accurate postnatal head circumference measurements are not possible.

For a study comparing head circumference measurements in utero to those obtained after birth, see: Melamed N, Yogev Y, Danon D, et al. Sonographic estimation of fetal head circumference: how accurate are we? Ultrasound Obstet Gynecol 2011;37:65-71.

In the setting of Zika virus infection, the head circumference might be disproportionately small in comparison with the length of the infant and not explained by other etiologies. View more information about Zika Virus Infection and Microcephaly.

Measuring a baby's head

Measuring Infant Head Circumference: An instructional video for healthcare providers

This video demonstrates how to measure the head circumference of an infant. Measuring head circumference is a primary way to determine the presence of microcephaly, which is important during this Zika outbreak. It is intended to help clinicians evaluate babies born to mothers infected with Zika virus.
Spanish | Italian

Top