Error found in standard guidelines on fetal varicella syndrome

The UK’s Drug and Therapeutics Bulletin (DTB), published by Which?, has identified an important error in standard guidelines on fetal varicella syndrome. This finding has major implications worldwide for advice given to women with chickenpox in late pregnancy.

Fetal varicella syndrome is an uncommon but potentially fatal condition that can affect the unborn child of a pregnant woman who catches chickenpox. It can cause problems such as skin loss or scarring, under-development or weakness of limbs and low birth weight.

National guidelines in, for example, the UK, USA, Ireland, New Zealand, Holland and Spain, have suggested that the risk of fetal varicella syndrome is confined to maternal chickenpox infection in the first 20 weeks of pregnancy. However, DTB has reported evidence that undermines this view, as do guidelines in Australia and Canada.

Recently published data have estimated the risk of fetal varicella syndrome in children exposed to chickenpox in the uterus at around 0.5 per cent after maternal infection at between two and 12 weeks of pregnancy; 1.4 per cent after infection at 12-28 weeks; and 0 per cent from 28 weeks onwards.1

These data are based on a recently published collation of evidence.2 Crucially, this collation includes a study that reported a case of fetal varicella syndrome following maternal infection at 24 weeks of pregnancy (in a total of 157 women infected after 20 weeks).3 The collation also included eight other published cases, from various countries, of fetal varicella syndrome where the mother was infected after the 20th week of pregnancy.4-11 There has also been a recently reported case, in France, of the syndrome after maternal infection in the 22nd week of pregnancy.12

In view of this evidence, DTB is urging advisory bodies worldwide to review their advice on the risk of fetal varicella syndrome. Already, in the UK, the Department of Health, Royal College of Obstetricians and Health Protection Agency have said they will be amending their guidance in response to DTB’s call for such action. Their advice will now reflect evidence that fetal varicella syndrome can occur following maternal chickenpox infection in the second half of pregnancy.

Dr Ike Iheanacho, editor, DTB, said:

“Guidance suggesting that fetal varicella syndrome can only occur in the first 20 weeks of pregnancy is at odds with published evidence.

“Such advice therefore needs to be revised worldwide as a matter of urgency. Until this happens, parents and healthcare professionals will be misinformed about an uncommon but highly dangerous complication of chickenpox infection in pregnancy.”