Mothers and infants transmit nutrients, hormones and antibodies through the blood in umbilical cord. However, HIV permeates the blood, thus entering the fetus from the mother.

During the prenatal period, a pregnant woman transmits pathogens to her offspring, which is called vertical transmission. This kind of transmission is between the pregnant woman and the fetus. Vertical propagation corresponds to horizontal transmission. Broadly speaking, vertical transmission can include the following ways:

Transplacental transmission: the infected pregnant woman infects the fetus through placental blood, which is called trans-placental transmission. There are rubella, hepatitis B, mumps, measles, chickenpox, cytomegalovirus infection, arbovirus infection, syphilis and other diseases transmitted through the placenta. If pregnant women suffer from rubella in the early pregnancy, it often harms the fetus and causes fetal malformation and congenital cataract.

Upward transmission: the pathogen reaches the chorion or placenta through the vagina of pregnant women, which causes fetal infection, which is called upward transmission. Such as Staphylococcus, Streptococcus, Escherichia coli, Pneumococcus and Candida albicans.

Transmission caused by childbirth: The fetus comes out of the sterile amniotic cavity and is exposed to the seriously polluted birth canal of the mother, and the skin, respiratory tract and intestine of the fetus are all exposed to pathogens. If there are pathogens such as gonococcus, conjunctivitis inclusion body and herpes virus in the birth canal of pregnant women, it may lead to corresponding infection.