Chickenpox exposure during pregnancy

By trimester

Weeks 1–13

1st trimester

A first infection now sits inside the window associated with congenital varicella syndrome, described as up to a 3 percent chance with first or early second trimester infection. Most babies in this situation are still healthy.

Weeks 14–27

2nd trimester

Weeks 13 to 20 carry the highest congenital varicella syndrome risk, around 2 percent, and that risk drops substantially once the fetus develops its own immune response after 20 weeks.

Weeks 28–birth

3rd trimester

The concern flips to timing around birth. Infection from 5 days before delivery to 1 or 2 days after leaves the newborn without transferred antibodies, while infection 6 to 21 days before delivery usually means a milder course.

What does the evidence show for chickenpox exposure?

• Varicella is highly contagious, with roughly a 90 percent chance of transmission within a household, and a blood test can show both an active infection and past immunity. 1
• Once someone recovers from varicella their body makes antibodies that usually last a long time and keep them from getting it again, which is why prior infection or vaccination changes the whole conversation. 1
• With a first or early second trimester infection the fetus has up to a 3 percent chance of congenital varicella syndrome, which can involve scarring, eye problems, growth restriction, or underdeveloped limbs, and most babies born to people who have varicella in pregnancy are healthy. 1
• The highest congenital varicella syndrome risk, roughly 2 percent, falls between 13 and 20 weeks of gestation, and drops substantially after 20 weeks as fetal immunity develops. 2
• Post-exposure steps are described on a tight clock, with serologic testing within about 48 hours of exposure and varicella-zoster immunoglobulin given to susceptible pregnant people within 72 to 96 hours. 2

When should I call my provider about chickenpox exposure?

Fever and body aches often appear before any rash does, then small reddish spots show up that blister and scab over, with new spots continuing to form for 3 to 5 days. Pregnant adults develop varicella pneumonia more often than children do, and it typically appears within the first week of the rash as fever, a dry cough, and shortness of breath, so those symptoms call for urgent same-day evaluation rather than home monitoring. Because post-exposure immunoglobulin is timed to a 72 to 96 hour window after exposure, call your provider the same day you learn of an exposure rather than waiting to see if a rash appears. Whatever the pattern, any symptom that feels beyond your usual range is a reason to call: obstetric teams expect these questions and would rather hear early than late.