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Zika and pregnancy ultrasound guidance (perhaps not just microc. and 1st trimester)– March 2016

ISUOG Interim Guidance on ultrasound for Zika virus infection in pregnancy: information for healthcare professionals

Note: ISOG = International Society of Ultrasound in Obstetrics and Gynecology
Ultrasound Obstet Gynecol 2016; 47: 530-532. 10 March 2016, DOI: 10.1002/uog.15896
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In response to the World Health Organization (WHO) statements and international concerns regarding the Zika virus (ZIKV) outbreak, ISUOG is publishing the following guidance for ultrasound during pregnancy.
With the current uncertainty regarding many aspects of the diagnosis and clinical course of ZIKV infection in pregnancy, potentially valuable information may be obtained by ultrasound practitioners that may help in counseling pregnant women and further improve our understanding of the pathophysiology of ZIKV infection in pregnancy.
This statement is not intended to replace previously published interim guidance on evaluation and management of ZIKV-exposed pregnant women.
It should therefore be considered in conjunction with other relevant advice from organizations such as:

There is an outbreak of ZIKV infection in the Americas, Caribbean and South Pacific1,2. The infection is spread mainly by Aedes mosquitoes, although a small number of cases from sexual transmission have been reported3. The wide distribution of the mosquito, combined with the lack of immunity in the population, has led to rapid evolution of the outbreak.
Most cases of ZIKV infection are self-limiting and without sequelae, but there have been cases of Guillain-Barre disease post-infection. In addition, clusters of cases of brain anomalies and microcephaly in some areas with known ZIKV transmission have been reported. This increased number of children with microcephaly has led to a high level of concern among pregnant women living in or traveling to endemic areas. ZIKV can cross the placenta and has been detected using polymerase chain reaction (PCR) analysis of amniotic fluid of pregnancies affected with fetal structural brain abnormalities and microcephaly4, and ZIKV has been isolated postmortem from the brain of a fetus with microcephaly5. A causal relationship between in-utero exposure to ZIKV and microcephaly is now likely, though not yet fully established6.
It should be remembered that, for fetal abnormalities to occur due to congenital infection, a number of steps are needed:

  • maternal exposure;
  • maternal infection;
  • fetal infection; and
  • fetal affection.

How these steps progress in ZIKV infection is unknown: we do not know how many women exposed in pregnancy become infected, how many of those infected will transmit to the fetus, and what proportion of infected fetuses will suffer effects. It is also important to note that, although microcephaly has been observed, this may well represent the severe end of the spectrum of effects and the co-existence of other abnormalities, while unknown, is likely. The gestational age at which infection occurs is important in other congenital infections, such as cytomegalovirus and toxoplasmosis, and it is probable that ZIKV infection poses the greatest risk in early pregnancy, although effects throughout pregnancy cannot be excluded confidently7.
As the situation is evolving rapidly, this guidance will be updated periodically.


National guidelines should be followed regarding testing. Expert opinion should be sought from national reference laboratories. In general, testing for ZIKV is possible in maternal serum by reverse transcription PCR (RT-PCR) or detection of ZIKV-specific IgM antibodies8,9. The limitation of RT-PCR testing is that it can detect ZIKV only during, or immediately following, acute infection. ZIKV IgM testing is problematic because of cross-reactivity with other Flaviviruses and some immunizations. This may lead to an unreliably high false-positive rate of ZIKV serological testing, but negative serology results may be of value in ‘ruling out’ past ZIKV infection. Expert interpretation of both is required and is beyond the scope of this guidance.

In pregnant women with ZIKV exposure and symptoms, positive Flavivirus serology or proven ZIKV infection, or in those with exposure and/or symptoms but who have not had positive serology results, referral for detailed ultrasound assessment is appropriate.
1) Accurate assignment of gestational age

  • Accurate estimation of gestational age (GA) is of the utmost importance in order to plot appropriately fetal growth, in particular head circumference (HC) growth.
  • Therefore, a careful assessment of existing scan results should be undertaken.
  • Fetal crown-rump length (CRL) measurement before 14 weeks is the most accurate method for GA assessment.
  • If this is not available a careful history should be taken to establish the last menstrual period and its reliability, and compared with the first reliable ultrasound.
  • The use of HC for GA estimation, especially in the third trimester, should be avoided.

2) Baseline ultrasound scan

  • A baseline ultrasound scan should be performed on referral. As a minimum this should involve the following.
  • In cases referred < 14 weeks:
    Measurement of fetal CRL, biparietal diameter (BPD) and HC.
    Assessment of fetal anatomy10.
  • In cases referred > 14 weeks:
  • Fetal biometry, including BPD, HC, abdominal circumference (AC) and femur length (FL)10,11.
  • Assessment of fetal anatomy11.
  • Measurement of the lateral ventricles and transcerebel- lar diameter (TCD)12.
  • In addition, and until more knowledge is acquired, assessment for intracerebral findings associated with other congenital infections, including presence of calcifications, periventricular or intraventricular echogenicities and irregularly shaped lateral ventricles13.

3) Subsequent ultrasound scans

  • It is not known if, or when, fetal signs occur following maternal ZIKV infection. Given the uncertainties around diagnosis, the ISUOG panel consensus is as follows:
    Careful assessment of the availability of resources should be undertaken, in order to prevent loss of important routine ultrasound examinations at population level for those women not exposed to ZIKV.
    On balance, ultrasound assessment as described above, should be performed every 4-6 weeks, if local resources permit.
    Given that interval growth is particularly relevant, an interval of 6 weeks is more likely to produce a robust diagnosis and reduce false-positive rates, but this needs to be balanced against later diagnosis.

4) Deviation from normal
If ultrasound assessment shows a fetal HC of 2 SD below the expected mean for gestational age, or a fetal brain abnormality (such as intracranial calcifications or ventriculomegaly), referral to a specialist center for detailed assessment, including neurosonography of the fetal brain, should be undertaken12.
Most fetuses in which the only finding is a HC of 2 SD below the mean would be expected to represent the lower end of the normal population distribution. An interval scan in 2-3 weeks should be arranged14,15.
Given the current uncertainty, existing evidence and experience from prenatal imaging findings in other infections should be taken into account; these include the presence of irregularly shaped ventricular margins, increased periventricular echogenicity with or without cystic lesions, intraventricular adhesions, calcifications, callosal or ver- mian dysgenesis, small TCD, enlarged cisterna magna and/or increased amount of cerebrospinal fluid around the brain4,13.
In cases in which subsequent scans show a further decline in fetal HC growth, to below -3 SD, or in those with definitive coexistent brain abnormalities, further assessment should include the following:
Discussion of the advantages and risks of an amniocentesis for ZIKV RT-PCR. Expert virology advice should be sought before any such procedure. The mother should be made aware that the sensitivity and specificity of this test for detecting congenital infection are unknown and that the likelihood of the fetus being affected is also unknown. However, in the case of a fetal brain abnormality on ultrasound and a positive ZIKV RT-PCR result, the likelihood of the two being associated is high.
Consideration of performance of fetal brain magnetic resonance imaging, if available, which may detect abnormalities that are not visible on ultrasound.
Depending on local laws, pregnancy termination may be discussed, based on GA and severity of the findings. Uncertainties regarding the condition should be made clear.
5) Postnatal assessment
Standardized HC measurements should be undertaken and plotted on standards that take into account GA at birth and sex16,17. The use of a single cut-off regardless of GA is not recommended18.
When there has been laboratory confirmation of maternal or fetal ZIKV infection8:
Placental histopathological examination and ZIKV testing of placental tissue and umbilical cord blood should be considered.
Babies should be followed up into childhood for signs of any adverse effects of congenital ZIKV infection.


This Interim Guidance was produced by the ISUOG ZIKV Rapid Response Group, members of which are:

  • T. Papageorghiou, Fetal Medicine Unit, St George’s University Foundation Hospitals NHS Trust, London, and Nuffield Department of Obstetrics and Gynaecology, University of Oxford, Oxford, UK
  • Thilaganathan, Fetal Medicine Unit, St George’s University Foundation Hospitals NHS Trust, London, UK
  • M. Bilardo, Department of Obstetrics, University Medical Centre Groningen, University of Groningen, Groningen, The Netherlands
  • A. Ngu, East Melbourne Ultrasound, East Melbourne, VIC, Australia
  • G. Malinger, Division of Ultrasound in Obstetrics & Gynecology, Lis Maternity Hospital, Tel Aviv Sourasky Medical Center, Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv, Israel
  • M. Herrera, Maternal Fetal Medicine Department, Colombian University Clinic, Colsanitas Clinic, Bogota, Colombia
  • L. J. Salomon, Department of Obstetrics and Maternal- Fetal Medicine, Necker-Enfants Malades Hospital, Assistance Publique-Hdpitaux de Paris, Universite Paris Descartes, Paris, France
  • L. E. Riley, Obstetrics and Gynecology, Massachusetts General Hospital, Boston, MA, USA J. A. Copel, Department of Obstetrics, Gynecology and Reproductive Sciences, Yale School of Medicine, New Haven, CT, USA


  1. European Centre for Disease Prevention and Control. Rapid risk assessment: Zika virus epidemic in the Americas: potential association with microcephaly and Guillain-Barre syndrome - 10 December 2015. Stockholm: ECDC; 2015. http://ecdc.europa.eu/en/publications/Publications/zika-virus-americas-association-with-microcephaly-rapid-risk-assessment.pdf [Accessed 7 February 2016].
  2. World Health Organization. Pregnancy management in the context of Zika virus. Interim guidance.
    http://www.who.int/csr/resources/publications/zika/pregnancy-management/en/ [Accessed 11 March 2016].
  3. Oster AM, Brooks JT, Stryker JE, Kachur RE, Mead P, Pesik NT, Petersen LR. Interim guidelines for prevention of sexual transmission of Zika virus - United States, 2016. MMWR Morb Mortal Wkly Rep 2016; 65: 120-121.
  4. Oliveira Melo AS, Malinger G, Ximenes R, Szejnfeld PO, Alves Sampaio S, Bispo de Filippis AM. Zika virus intrauterine infection causes fetal brain abnormality and microcephaly: tip of the iceberg? Ultrasound Obstet Gynecol 2016; 47: 6-7.
  5. Mlakar J, Korva M, Tul N, Popovic M, Poljsak-Prijatelj M, Mraz J, Kolenc M, Resman Rus K, Vesnaver Vipotnik T, Fabjan Vodusek V, Vizjak A, Pizem J, Petrovec M, Avsic Zupanc T. Zika Virus Associated with Microcephaly. N Engl J Med 2016 Feb 10. DOI: 10.1056/NEJMoa1600651. [Epub aheadofprint].
  6. Victora CG, Schuler-Faccini L, Matijasevich A, Ribeiro E, Pessoa A, Barros FC. Microcephaly in Brazil: how to interpret reported numbers? Lancet 2016; 387: 621-624.
  7. Schuler-Faccini L, Ribeiro EM, Feitosa IM, Horovitz DD, Cavalcanti DP, Pessoa A, Doriqui MJ, Neri JI, Neto JM, Wanderley HY, Cernach M, El-Husny AS, Pone MV, Serao CL, Sanseverino MT; Brazilian Medical Genetics Society-Zika Embryopathy Task Force. Possible association between zika virus infection and microcephaly - Brazil, 2015. MMWR Morb Mortal Wkly Rep 2016; 65: 59-62.
  8. Royal College of Obstetricians & Gynaecologists. Interim RCOG/RCM/ PHE/HPS clinical guidelines on Zika Virus Infection and Pregnancy: Information for Healthcare Professionals. https://www.rcog.org.uk/globalassets/documents/news/zika-virus-interim-guidelines.pdf.
  9. http://www.cdc.gov/zika/hc-providers/diagnostic.html Accessed 7 February 2016.
  10. Salomon LJ, Alfirevic Z, Bilardo CM, Chalouhi GE, Ghi T, Kagan KO, Lau TK, Papa- georghiou AT, Raine-Fenning NJ, Stirnemann J, Suresh S, Tabor A, Timor-Tritsch IE, Toi A, Yeo G. ISUOG practice guidelines: performance of first-trimester fetal ultrasound scan. Ultrasound Obstet Gynecol 2013; 41: 102-113.
  11. Salomon LJ, Alfirevic Z, Berghella V, Bilardo C, Hernandez-Andrade E, Johnsen SL, Kalache K, Leung KY, Malinger G, Munoz H, Prefumo F, Toi A, Lee W; ISUOG Clinical Standards Committee. Practice guidelines for performance of the routine mid-trimester fetal ultrasound scan. Ultrasound Obstet Gynecol 2011; 37: 116-126.
  12. International Society of Ultrasound in Obstetrics & Gynecology Education Committee. Sonographic examination of the fetal central nervous system: guidelines for performing the ‘basic examination’ and the ‘fetal neurosonogram’. Ultrasound Obstet Gynecol 2007; 29:109-116.
  13. Malinger G, Lev D, Zahalka N, Ben Aroia Z, Watemberg N, Kidron D, Sira LB, Lerman-Sagie T. Fetal cytomegalovirus infection of the brain: the spectrum of sonographic findings. Am J Neuroradiol 2003; 24: 28-32.
  14. Deloison B, Chalouhi GE, BernardJP, Ville Y, Salomon LJ. Outcomes of fetuses with small head circumference on second-trimester ultrasonography. Prenat Diagn 2012; 32: 869-874.
  15. Leibovitz Z, Daniel-Spiegel E, Malinger G, Haratz K, Tamarkin M, Gindes L, Ben-Sira L, Lev D, Shapiro I, Bakry H, Weizman B, Zreik A, Egenburg S, Arad A, Tepper R, Kidron D, Lerman-Sagie T. Microcephaly at birth - the accuracy of three references for fetal head circumference. How can we improve prediction? Ultrasound Obstet Gynecol 2015 Oct 29. DOI: 10.1002/uog.15801. Epub ahead of print.
  16. World Health Organization. The WHO Child Growth Standards. http://www.who.int/childgrowth/standards/en/. Accessed 26 February 2016.
  17. Villar J, Cheikh Ismail L, Victora CG, Ohuma EO, Bertino E, Altman DG, Lambert A, Papageorghiou AT, Carvalho M, Jaffer YA, Gravett MG, Purwar M, Frederick IO, Noble AJ, Pang R, Barros FC, Chumlea C, Bhutta ZA, Kennedy SH; International Fetal and Newborn Growth Consortium for the 21st Century (INTERGROWTH-21st). International standards for newborn weight, length, and head circumference by gestational age and sex: the Newborn Cross-Sectional Study ofthe INTERGROWTH-21st Project. Lancet 2014; 384: 857-868.
  18. World Health Organization. Assessment of infants with microcephaly in the context of Zika virus. Interim guidance.
    http://www.who.int/csr/resources/publications/zika/assessment-infants/en/ Accessed 26 February 2016.

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