If you’re pregnant and not already immune to hepatitis B, vaccination is recommended during pregnancy itself, particularly if you have risk factors for infection. There is no single “best trimester” mandated by guidelines. The timing depends on your screening results and risk level, but the vaccine is considered safe at any point during pregnancy.
Screening Comes First
Every pregnant person should be screened for hepatitis B surface antigen (HBsAg) during each pregnancy, preferably in the first trimester. This applies regardless of whether you’ve been vaccinated before, tested negative in a previous pregnancy, or have no known risk factors. A positive result means you currently have an active hepatitis B infection, which changes the plan entirely: instead of vaccination, your care team will focus on preventing transmission to your baby at birth.
If your screening comes back negative, the next question is whether you’re already immune from past vaccination. If blood work shows you’re susceptible (no protective antibodies) and you have risk factors for hepatitis B, such as a sexual partner who is infected, exposure to blood through your work, or injection drug use, vaccination during pregnancy is recommended. If you don’t have clear risk factors, your provider may offer vaccination after delivery instead.
Timing During Pregnancy
Guidelines do not restrict the hepatitis B vaccine to a particular trimester. Unlike some vaccines that are specifically timed (the Tdap shot, for example, is typically given between weeks 27 and 36), the hepatitis B vaccine can be given whenever it’s needed. In practice, if you’re identified as susceptible and at risk during that first-trimester screening, vaccination can begin right away.
The standard hepatitis B vaccine series requires multiple doses. Depending on the vaccine used, that means either two or three shots spread over weeks to months. It is perfectly acceptable to start the series during pregnancy and finish it after delivery. You don’t need to restart the series if there’s a gap between doses.
Which Vaccines Are Approved
As of September 2024, all four hepatitis B vaccines available in the United States are approved for use in pregnant people: Engerix-B, Recombivax HB, Heplisav-B, and Twinrix (a combination hepatitis A and B vaccine). This is a meaningful update because Heplisav-B, which uses a newer type of immune-boosting ingredient and requires only two doses instead of three, was previously not labeled for use during pregnancy. The FDA updated its labeling in 2024 to include pregnant patients, giving providers more flexibility.
Safety for You and the Baby
Hepatitis B vaccines are inactivated, meaning they contain no live virus. They cannot cause hepatitis B infection in you or your baby. Post-marketing safety data comparing the two main vaccine types found no increased risk of miscarriage, preterm birth, low birth weight, or birth defects among vaccinated pregnant people. Miscarriage rates were 7.4% with the newer vaccine and 16.8% with the traditional version, both within or below the general population’s expected range of 10% to 20%. Preterm birth rates were essentially identical between groups at around 14%. No major birth defects were identified in infants followed through six months of age.
Why It Matters During Pregnancy
Hepatitis B passes from mother to baby during childbirth. Without intervention, a baby born to an infected mother has up to a 90% chance of developing chronic hepatitis B, which can lead to serious liver disease later in life. The point of screening and vaccinating during pregnancy is to close that window of risk. If you’re already immune before delivery, you can’t become infected late in pregnancy and unknowingly pass the virus to your newborn.
Even with perfect maternal screening, the system has a backup layer. All newborns receive their first hepatitis B vaccine dose within 24 hours of birth, regardless of the mother’s status. Babies born to mothers who test positive also receive a protective antibody injection (immunoglobulin) at the same time. The infant series continues with additional doses at one to two months and again at six months of age, with the final dose given no earlier than 24 weeks (about five and a half months).
Finishing the Series After Delivery
If you start your vaccine series during pregnancy but don’t complete all doses before giving birth, you can safely finish it while breastfeeding. The vaccine does not affect breast milk safety or your baby’s health. In fact, breastfeeding has been shown to improve an infant’s immune response to their own hepatitis B vaccination series. There’s no need to delay doses or pump and discard milk after receiving a shot.
The 2024 Universal Recommendation
The Advisory Committee on Immunization Practices now recommends universal hepatitis B vaccination for all adults aged 19 to 59, including pregnant people. This means the conversation about hepatitis B vaccination is no longer limited to those with obvious risk factors. If you’re under 60, were never vaccinated as a child or young adult, and are now pregnant, your provider should be offering you the vaccine as part of routine prenatal care. Adults 60 and older can also receive the vaccine if they have risk factors.
This universal recommendation simplifies things: rather than trying to assess every patient’s individual risk profile (which can miss people), the default is to vaccinate anyone who isn’t already protected. For pregnant patients specifically, this means the question has shifted from “should I get this vaccine?” to “which dose am I on?”