Intended for healthcare professionals

Practice Clinical updates

Fetal microcephaly

BMJ 2018; 361 doi: (Published 04 June 2018) Cite this as: BMJ 2018;361:k2232
  1. Aamod Nawathe, subspecialty trainee in fetal maternal medicine1,
  2. Jane Doherty, general practitioner2,
  3. Pranav Pandya, consultant and lead in fetal medicine1
  1. 1Fetal Maternal Medicine, University College London Medical School, London WC1E 6BT, UK
  2. 2Nexus Health Group, London SE1 6JP
  1. Correspondence to: P Pandya pranavpandya{at}

What you need to know

  • Fetal microcephaly can be isolated or be associated with other congenital anomalies

  • Causes include genetic, chromosomal, infections, exposure to toxins (such as alcohol), metabolic, intrauterine growth restriction, or a normal variant

  • The consequences of microcephaly can include neurodevelopmental delay, cerebral palsy, epilepsy, and problems with eyesight and hearing

  • There is no treatment that can reverse the effects of microcephaly in utero

  • Advise women diagnosed with primary toxoplasmosis or cytomegalovirus infection to wait for at least six months before conception

Fetal microcephaly, a small head circumference in utero or at birth is a rare but important clinical finding that may occur as part of a range of conditions or, rarely, as a normal variant. The prevalence of prenatal microcephaly in Europe is 1.53 per 10 000,1 2.3 per 10 000 in India,2 and about 6 per 10 000 in the US.3 Identifying microcephaly is important because the smaller the fetal head circumference the greater the risk of developmental and intellectual delay.4

Although there is no treatment available, early diagnosis allows for timely investigations, as well as allowing parents to receive appropriate counselling about long term prognosis. This update discusses the diagnosis and management of fetal microcephaly, and is aimed at obstetricians, midwives, and general practitioners.

Sources and selection criteria

We searched PubMed and the Cochrane Library using the MESH term “microcephaly” and subheadings such as Zika virus, preconception counselling, prenatal diagnosis, toxoplasmosis, and cytomegalovirus. Our search included randomised controlled trials, systematic and observational reviews and relevant case reports from 1965 to 2017. We excluded non-English articles without reliable translation or other internet sources of uncertain accuracy.

What is fetal microcephaly?

Microcephaly is a head circumference significantly smaller than the average for the gestational age (fig 1).6 Fetal microcephaly has been defined as head circumference smaller than 3 standard deviations below the mean.78

Fig 1

Range of microcephaly. …

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