Highest transmission of hepatitis B from mother to fetus occurs if the mother is infected during:
Viral hepatitis is the commonest cause of jaundice in pregnancy in the tropics.
Hepatitis A (HAV):

Infection is spread by faecal-oral route.
Diagnosis is confirmed by detection of IgM antibody to hepatitis A (anti HAV Igm).
Disease is usually self limited and fulminant hepatitis is rare.
Perinatal transmission is rare, chronic carrier state does not exist.
The virus is not teratogenic.
Pregnant woman exposed to HAV infection should receive immunoglobulin 0.02 ml/kg within 2 weeks of exposure. She should also have hepatitis A vaccine single dose 0.06 ml IM. It is safe in pregnancy.

Hepatitis B virus (HBV):

The virus is transmitted by parenteral route, sexual contact, vertical transmission and also through breast milk.
The risk of transmission to fetus ranges from 10% in first trimester to as high as 90% in third trimester and it is specially high (90%) from those mothers who are seropositive to hepatitis B surface antigen (HBsAg) and ‘e’-antigen (HBeAg).
Neonatal transmission mainly occurs at or around the time of birth through mixing of maternal blood and genital secretions. Approximately 25% of the carrier neonate will die from cirrhosis or hepatic carcinoma, between late childhood to early adulthood.
HBV is not teratogenic.
Ist trimester
IInd trimester
IIIrd trimester
At the time of implantation