Infectious Diseases in Pregnancy: Baby has low risk of contracting varicella virus from mom-to-be

By Jenny Manzer

Women infected with the varicella virus during pregnancy are at low risk of having a baby with congenital varicella syndrome, a prospective multi-centre study shows.

In the past, infected women have terminated pregnancies rather than risk having a baby with the devastating syndrome, which can include chorioretinitis, congenital cataracts, brain damage, limb atrophy and other anomalies.

"In a very carefully done prospective study with thorough evaluation of the newborns up to two years of age, the incidence of congenital varicella syndrome is lower than has been reported previously," said lead researcher Dr. James Harger, a retired professor of obstetrics and gynecology at the University of Pittsburgh.

The team prospectively studied a cohort of about 350 women infected with varicella zoster virus.

Of the women's 231 infants who underwent all three follow-up exams, the team found only one definite case of the syndrome, for an incidence rate 0.4%?lower than earlier published figures.

Subjects were enrolled at 10 U.S. centres from 1993 to 1996. The women came from diverse ethnic and socioeconomic backgrounds, and contracted the virus at different stages in pregnancy.

About 39% showed rash onset in the first trimester, 34% in the second and 28% in the third.

Neonates were examined at zero to six months, seven to 18 months, and 19 to 30 months after delivery for abnormalities of their physical and developmental features. The babies had their eyes and hearing examined by specialists.

In the past, the limited information on varicella during pregnancy led physicians to cite alarming risks to exposed women, Dr. Harger said.

Early studies into the incidence of the syndrome among infected women reported rates ranging from 2% to 9%.

"The earlier studies that quoted the higher percentages were not done prospectively," Dr. Harger said. "There were flaws in the methods."

Although later, larger studies reported lower rates ranging from 0% to 1.5%, they did not include a consistent and thorough examination of the infants for eye defects.

The only case of the syndrome found in the Pittsburgh-led study was confirmed by eye examination.

The infant, born to a mother who had contracted the virus at 24 weeks, had a left retinal macular lesion and typical skin scars.

Dr. Harger's study, recently published in Obstetrics & Gynecology, follows on the heels of work by the Motherisk team at Toronto's Hospital for Sick Children.

Motherisk director Dr. Gideon Koren said their published findings suggested the risk of a varicella-infected women having a baby with the syndrome is about 1%?which is the figure they tell patients.

Dr. Koren suspects clinicians are still giving women old risk estimates, however. Many are also not aware immediate administration of antibodies can mitigate the effects of the virus, he said.

He noted a pregnant patient often becomes concerned about exposure when chicken pox is going around her children's school or daycare.

He said seven out of 10 times, women who thought they never had chicken pox will be found to have the antibodies upon testing. The test for antibodies needs to be done quickly, within a day, Dr. Koren stressed. "The time is crucial," he said, noting that during the prodromal phase the virus is highly effective at crossing the placenta. Unfortunately, it's not always possible to have the blood test done soon enough, in which case the patient should be given Varicella-zoster immune globulin (VZIG).

Research, including studies from Motherisk, has suggested VZIG can prevent or attenuate the harmful effects of the virus in exposed patients if given soon after infection. Clinicians can get VZIG free by calling the Red Cross, Dr. Koren said.

If these measures fail and the woman is infected, however, families need to be informed about the risks, he said. As both the Toronto and the Pittsburgh research indicated, the risk is very small, he said. "But it's a true risk." He also noted the 1% risk of varicella syndrome compounds the patient's existing 3% risk of having a baby with a birth defect, pushing it up to 4%. Unlike Down syndrome, there is no test for congenital varicella syndrome, which produces high anxiety in patients. Dr. Koren said women with varicella appear less likely to terminate their pregnancies if they receive good information from their doctors. "The message is, 'Be careful that women understand what you say,' " Dr. Koren advised.

Ideally, he said, now that the vaccine is available, all Canadian women of child-bearing age who suspect they did not have chicken pox should be tested, then vaccinated if they do not have the antibodies. Back to Contents

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