Hepatitis B pada Kehamilan

01Pathophysiology

HBV is a partially double-stranded DNA virus that replicates through an RNA intermediate using its own reverse transcriptase. The virus itself is not directly cytopathic. Instead, liver damage results from the host immune response directed against infected hepatocytes displaying viral antigens on their surface. This is why immunotolerant patients (such as those infected perinatally) can carry very high viral loads for decades with minimal liver inflammation, while a robust immune response in adulthood causes more symptomatic hepatitis but also a higher chance of viral clearance.

In pregnancy, the critical concern is vertical transmission, which occurs predominantly during labor and delivery through the neonate's exposure to maternal blood and cervicovaginal secretions. The risk of transmission correlates directly with maternal viral load and HBeAg status. Mothers who are both HBsAg (+) and HBeAg (+) with high viral loads carry a vertical transmission rate of 70 to 90% without intervention. Mothers who are HBsAg (+) but HBeAg (-) have a lower but still notable risk of roughly 10 to 40%.

The reason perinatal infection is so consequential is the inverse relationship between age at infection and chronicity. Neonates infected at birth have a 90% chance of developing chronic HBV infection, compared to roughly 5% in immunocompetent adults. Chronic infection acquired perinatally leads to decades of viral replication, progressive hepatic fibrosis, and a significantly elevated lifetime risk of hepatocellular carcinoma and cirrhosis. This is the foundational rationale behind universal prenatal screening and aggressive neonatal immunoprophylaxis.

Transplacental transmission (in utero) accounts for a smaller fraction of cases and is thought to occur through placental breaches or high-level viremia crossing the placental barrier. This route is less amenable to postnatal immunoprophylaxis alone, which is precisely why maternal antiviral therapy in the third trimester has been added to guidelines for women with very high viral loads.

02Classification and Clinical Manifestation

HBV Serologic Phases in Chronic Infection

03Diagnostic Workup

HBsAg is the universal prenatal screening test and is recommended for all pregnant women at the first prenatal visit, regardless of vaccination history or prior testing. This is the single most important step and the one most commonly tested. A positive HBsAg triggers the full serologic workup.

Once HBsAg is confirmed positive, the next step is to check HBeAg, Anti-HBe, and a quantitative HBV DNA viral load. The viral load is the key decision point for antiviral therapy. ALT should also be obtained to determine whether the patient is in an immune-active phase. If ALT is elevated and the patient has not been previously evaluated, hepatology or infectious disease referral is appropriate.

A common exam scenario presents a woman who was vaccinated but still tests HBsAg (+). This tests your understanding that the vaccine contains only recombinant HBsAg protein and produces Anti-HBs antibodies. A vaccinated person should be HBsAg (-) and Anti-HBs (+). If HBsAg is positive, the patient has true infection, not a vaccine artifact.

For women with unknown HBsAg status at the time of delivery, rapid HBsAg testing should be performed, and the neonate should receive the HBV vaccine birth dose within 12 hours regardless. HBIG should be administered as soon as the maternal result returns positive (and no later than 7 days of life).

04Management and Treatment

Maternal antiviral therapy is the primary exam-tested intervention. Current guidelines recommend initiating tenofovir disoproxil fumarate (TDF) 300 mg orally once daily beginning at 28 to 32 weeks of gestation in women with HBV DNA levels exceeding 200,000 IU/mL. The goal is to reduce viral load before delivery, thereby decreasing the risk of immunoprophylaxis failure in the neonate. TDF is the preferred agent because of its Pregnancy Category B safety profile, high barrier to resistance, and extensive safety data in pregnancy (largely from HIV treatment cohorts). Tenofovir alafenamide (TAF) has less pregnancy safety data and is generally not the first-line choice, though emerging data suggest comparable safety.

Entecavir is not recommended in pregnancy (Category C, limited data, embryotoxic in animal studies). If a woman is on entecavir pre-conception, she should be switched to TDF before or early in pregnancy.

Regarding timing of discontinuation, if antiviral therapy was started solely for prevention of vertical transmission (not for maternal disease), TDF can be discontinued after delivery or at the time of the first postpartum visit. However, close monitoring of ALT is required in the postpartum period because hepatitis flares can occur after withdrawal of antiviral therapy or after the immune reconstitution that follows delivery. If the mother has underlying chronic active hepatitis requiring long-term treatment, TDF should be continued indefinitely.

Neonatal immunoprophylaxis consists of two components administered within 12 hours of birth: the first dose of the HBV vaccine series (given intramuscularly in the anterolateral thigh) and HBIG 0.5 mL intramuscularly at a separate injection site. The vaccine series is then completed at 1 month and 6 months of age. Post-vaccination serologic testing (HBsAg and Anti-HBs) should be performed at 9 to 12 months of age (or 1 to 2 months after the final vaccine dose) to confirm successful immunization and rule out chronic infection.

Breastfeeding is not contraindicated in HBsAg-positive mothers, provided the neonate has received appropriate immunoprophylaxis. HBV is present in breast milk in small quantities, but the combination of vaccine and HBIG is sufficient to prevent transmission through this route. The only contraindication to breastfeeding would be cracked or bleeding nipples with active viral shedding, though even this is debated and not universally agreed upon.

Mode of delivery: HBV status alone is not an indication for cesarean section. Unlike hepatitis C or HIV (where viral load-driven cesarean recommendations exist), elective cesarean delivery has not been shown to reduce vertical HBV transmission when immunoprophylaxis and maternal antivirals are properly administered. Prolonged rupture of membranes should be avoided when possible, but this is general obstetric management and not an HBV-driven recommendation tested in isolation.

05Differential Diagnosis and Distractors

06Traps and High-Yield Pearls

The single most common trap on this topic involves confusing serologic markers. Vignettes will present a pregnant woman who is HBsAg (+) and HBeAg (+) and ask for the next best step. Students who do not check the viral load before initiating therapy, or who initiate the wrong antiviral (entecavir instead of tenofovir), will get the question wrong. The tested concept is recognizing that HBeAg positivity alone does not automatically trigger antiviral therapy in pregnancy; it is the quantitative HBV DNA level exceeding 200,000 IU/mL that determines the need for TDF.

Another frequently tested trap involves the timing and components of neonatal immunoprophylaxis. The exam will test whether you know that both vaccine and HBIG must be given within 12 hours, not 24 or 48 hours. Students who select "administer vaccine at routine well-child visit" will miss the critical birth-dose timing. Additionally, HBIG alone without vaccine (or vaccine alone without HBIG) is an incomplete answer for infants born to HBsAg-positive mothers.

A third trap involves breastfeeding. The vignette may present a newly postpartum HBsAg-positive mother and ask whether breastfeeding should be restricted. The correct answer is that breastfeeding is permitted after the neonate has received immunoprophylaxis. Selecting "contraindicated" is a common error driven by the misconception that HBV in breast milk poses a meaningful risk after proper vaccination and HBIG.

Finally, do not recommend cesarean section solely based on HBV status. Unlike certain HIV scenarios, there is no evidence that elective cesarean reduces vertical HBV transmission when appropriate antiviral and immunoprophylaxis measures are in place. The core competency being tested across all these scenarios is your ability to sequence interventions correctly: screen universally with HBsAg, risk-stratify with HBeAg and viral load, treat with TDF when indicated at 28 to 32 weeks, and ensure dual neonatal immunoprophylaxis within 12 hours of birth.