10.4 The physiology of the placenta:
Role of the placenta in the feto-maternal exchange processes

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Sexually transmitted diseases:

• After the 5th month of pregnancy treponema pallidum bacteria, the syphilis pathogen, can pass through the placental barrier. The infection of the fetus can lead to a miscarriage or leave behind congenital abnormalities.
  
• In industrialized countries, the HIV transmission from the mother to the fetus amounts to roughly 15 to 25%. It depends on the viremia status of the mother. There are a variety of transmission possibilities, but the transplacental infection with HIV during or shortly before birth appears to be the most frequent. Probably infection frequently also occurs during the passage of the child through the maternal birth canal (HIV in the cervix mucus).
  
  The following precautionary measures can be taken.
  
  • Anti-HIV treatment during the pregnancy and birth as well as further treatment of the newborn during the first few weeks.
  • Birth via caesarian section
  • No breastfeeding of the child
    
    When all of these measures have been carried out the risk of infection for the baby can be reduced to below 1%.
    
    
• Gonorrhea (Neisseria gonorhoeae) arises through infection with gonococci. The child can be infected via vertical transmission (during birth) and develop an infection of the eyes (blennorrhoea neonatorum).

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Fetotoxic infections:

• The rubella virus may be responsible for a miscarriage during pregnancy (before the first month), for embryopathies (when the virus invades between the 1rst and 3rd month) or for fetopathies (after the 3rd month).
• Toxoplasmosis (caused by a protozoic parasite) is harmless for the mother, but can cause severe anomalies in the fetus.
• Listeriosis (traced back to a gram-positive Listeria monocytogenes) can be responsible for miscarriages, intrauterine death or neonatal sepsis due to transplacental infection or for secondary late meningitis due to a contaminated birth passage.
• The cytomegalovirus is generally the cause of infections that remain subclinical. It can also be responsible for miscarriages as well as for microcephaly and growth retardation. The infection happens transplacental or during birth.
• With herpes simplex genitalis a risk of neonatal contamination exists through infection in the birth canal.
• The parvovirus B19 is responsible for aplastic crises in utero (marked decrease of blood cells).
• Myobacterium tuberculosis, the tuberculosis pathogen, practically never passes through the placental barrier.

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The same is true for certain medications the teratogenic effects of which are today well documented.
Thalidomide, mainly responsible for phocomelia (prescribed in the 60's), as well as Roaccutane ® (retinoic acid, commonly used for treating acne), are highly teratogenic. The consumption of barbiturates, drugs and alcohol during pregnancy are also to be avoided!