Varicella in Pregnancy
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Direct answer
Chickenpox in a pregnant woman threatens three patients at once: the mother (pneumonitis, worst in the third trimester and in smokers), the fetus (congenital varicella syndrome when infection strikes before 20 weeks — overall fetal risk roughly 1-2 per cent, highest at 13-20 weeks), and the newborn (severe disseminated varicella when the mother's rash appears from five days before to two days after delivery, before antibody crosses). Oral aciclovir 800 mg five times daily for seven days, started within 24-48 hours of rash onset, treats the mother; varicella-zoster immunoglobulin 125 IU per 10 kg body weight (maximum 625 IU) is given within ten days of a significant exposure to a non-immune woman; and the peripartum newborn with exposure receives varicella-zoster immunoglobulin plus aciclovir.
What you must remember
- Trimester logic: before 20 weeks, congenital varicella syndrome (limb hypoplasia, cutaneous scarring in a dermatomal pattern, cataract, cortical atrophy, microcephaly); around 13-20 weeks carries the peak (about 2 per cent) risk; maternal rash at 5 days before to 2 days after delivery risks severe neonatal disease.
- Maternal risk: varicella pneumonia, likelier in the third trimester and in smokers — these women need intravenous aciclovir 10 mg/kg every eight hours and hospitalisation.
- Treatment dose: oral aciclovir 800 mg five times daily for seven days if within 24-48 hours of rash onset, beyond 20 weeks of gestation; before 20 weeks the decision is individualised but aciclovir is commonly used.
- Post-exposure prophylaxis: varicella-zoster immunoglobulin 125 IU per 10 kg intramuscularly, maximum 625 IU, as soon as possible within 10 days of exposure, for pregnant women without evidence of immunity.
- Immunity check: a reliable history counts; if uncertain, test varicella-zoster IgG urgently — a result within 24-48 hours decides whether immunoglobulin is needed.
- Neonatal protocol: rash in the mother from 5 days before to 2 days after birth — the neonate receives varicella-zoster immunoglobulin and aciclovir is considered; rash more than 5 days before delivery transfers protective IgG, and rash more than 2 days after delivery leaves the baby exposed but partly protected.
- Prevention: varicella vaccine (live) is contraindicated in pregnancy and pregnancy should be avoided for one month after vaccination — a preconception-care checkpoint; and herpes zoster in the mother does not cause congenital varicella syndrome.
A worked timeline
A primary school teacher at 16 weeks has never had chickenpox; her son develops vesicles on a Monday. Her IgG is negative, so within the window she receives varicella-zoster immunoglobulin 625 IU intramuscularly (60 kg, five 125 IU vials), which attenuates rather than prevents infection. She still develops a centripetal vesicular rash two weeks later — oral aciclovir 800 mg five times daily begins, with isolation from other pregnant women and neonates and a low threshold for admission: breathlessness or chest pain means a chest radiograph and intravenous aciclovir for pneumonitis. Infection at 16 weeks leaves the fetus about a 2 per cent risk; detailed anomaly scans look for limb hypoplasia, but no prenatal test reliably excludes the syndrome.
Rewind to 38 weeks: the same rash now puts the delivery date in the danger window. The plan — delay delivery a few days where feasible to let IgG cross (after day five post-rash), and keep varicella-zoster immunoglobulin and aciclovir ready in the nursery; a baby receiving prophylaxis need not be separated from the mother.
How the exam frames it
The screening question is almost always date arithmetic: "rash two days after delivery — what does the neonate need?" (varicella-zoster immunoglobulin with or without aciclovir), or "at which gestation is congenital varicella syndrome most likely?" (13-20 weeks, not the whole pregnancy). Distractors include zoster reactivation (shingles transmits chickenpox to susceptible contacts but the immune fetus is protected) and the vaccine (live, contraindicated, avoid conception for a month). The aciclovir dose (800 mg five times daily) and the immunoglobulin dose (125 IU per 10 kg, maximum 625 IU) are the two pure number items this topic yields; both are verified in current guidance, though varicella-zoster immunoglobulin supply in India is limited and pooled immunoglobulin is sometimes the practical substitute.
Frequently asked questions
What is the risk period for congenital varicella syndrome?
Maternal primary chickenpox before 20 weeks, the highest fetal risk (about 2 per cent) between 13 and 20 weeks.
When does the newborn face severe varicella?
When the mother's rash onset falls between five days before and two days after delivery, leaving no time for protective IgG transfer; the neonate receives varicella-zoster immunoglobulin and aciclovir is considered.
What is the dose of varicella-zoster immunoglobulin in pregnancy?
125 IU per 10 kg body weight intramuscularly, maximum 625 IU, given as soon as possible within 10 days of significant exposure to a woman without immunity.
What aciclovir regimen treats chickenpox in the pregnant mother?
Oral aciclovir 800 mg five times daily for seven days when started within 24-48 hours of rash onset; intravenous aciclovir 10 mg/kg every eight hours for pneumonitis or other severe disease.
Can the varicella vaccine be given during pregnancy?
No — it is a live attenuated vaccine, contraindicated until after delivery, with pregnancy advised against for one month following vaccination.