Case 63: Chicken pox exposure in pregnancy

 

Case 63: Chicken pox exposure in pregnancy

CASE 63: CHICKEN POX EXPOSURE IN PREGNANCY

A woman has telephoned the antenatal clinic for advice. She is 16 weeks’ gestation in her

second pregnancy. She took her son to a birthday party yesterday and has been telephoned

now by the party host to say that one of the other children at the party has just developed a

typical chicken pox rash.

She is worried about the effect of chicken pox on her pregnancy.

Questions

• What, if any, further questions do you need to ask her?

• What investigations should be performed?

• How will you advise and manage the case depending on the investigation results?100 Cases in Obstetrics and Gynaecology

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ANSWER 63

Chicken pox (caused by varicella zoster virus) is a very common, highly contagious and generally self-limiting mild childhood illness, mostly spread by respiratory droplets. Ninety per cent

of antenatal women will have been previously infected with chicken pox and immunity can

be demonstrated by the presence of varicella zoster virus (VZV) IgG antibodies in the serum.

Questions to be asked

• Does the woman know whether she has had chicken pox before?

• What was the nature of her contact with the affected child?

• What was the duration of her contact with the affected child?

When asked she can’t remember whether or not she had chicken pox as a child. It was an

indoor party and she herself had stayed at the party with her son for about 30 minutes.

Investigations to be performed

In many cases, a blood sample will have been retained from the antenatal booking blood tests

that can be tested for VZV immunoglobulin (IgG). Otherwise the woman should be asked

to have blood taken urgently for VZV IgG (ideally taken at the general practitioner’s practice

so that she does not attend the antenatal clinic and potentially infect other non-immune

pregnant women).

Advice and management

If the serum varicella IgG is positive then immunity is confirmed and the woman can be

reassured that neither she nor her fetus is at risk of infection.

Maternal risks

If the IgG is negative then she is not immune and more than 15 minutes in the same room

as the infected individual is sufficient to place her at risk of infection. She should be given

varicella immunoglobulin VZIG as soon as possible (effective if given up to 10 days after contact). She should then be advised that she is still potentially infectious and to avoid any other

pregnant women during the infectious period of 8–28 days after exposure.

The risk of maternal varicella to the mother is greater than in the mild childhood form of

the illness. Pneumonia, encephalitis and hepatitis are the potential complications. Maternal

death is reported in 1 per cent of affected pregnant women (five times higher than in nonpregnant women). If she is infected then the rash would be expected to appear within 1–3

weeks. She must be advised to seek medical attention at the outset of a rash developing and

should be prescribed acyclovir orally at the start of symptoms. She must be referred to hospital for supportive care and intravenous acyclovir if chest symptoms, neurological symptoms

or a haemorrhagic rash occurs.

Fetal risks

The risk of miscarriage is not increased in women who develop chicken pox in the first trimester. However fetal varicella syndrome (skin scarring, limb hypoplasia and neurological

abnormalities) may occur in 1 per cent of fetuses of women infected up to 28 weeks, as a result

of herpes zoster reactivation after the initial infection. Specialist fetal medicine ultrasound

5 weeks after initial infection may detect the anatomical abnormalities. If infection occurs

before 12 weeks’ gestation the chance of varicella syndrome is much lower.Case 63: Chicken pox exposure in pregnancy

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Maternal infection at term carries the risk of varicella of the newborn which is a severe

infection with up to 30 per cent mortality if untreated. The risk is approximately 30 per

cent in infants of mothers infected 1–4 weeks before delivery, with highest risk conferred if

infection is within 7 days of delivery. If possible delivery should therefore be delayed until

after recovery from maternal infection to allow transplacental transfer of maternal antibodies to the fetus. VZIG should be given to the susceptible neonate.

If the woman is non-immune but does not develop the infection then vaccination should be

recommended after delivery.

KEY POINTS

• Chicken pox in pregnancy is potentially much more severe than in nonpregnant

adults, with maternal death reported in up to 1 per cent of affected women.

• VZV is spread by respiratory droplets with same room contact for more than 15

minutes considered to place a nonimmune woman at high risk.

• VZIgG should be given as soon as possible after exposure.

• Fetal risks of maternal chicken pox infection are fetal varicella syndrome (if mother

infected before 28 weeks) or varicella of the newborn (if mother infected 1–4 weeks

before delivery).