Infections can get into the body through several routes. Respiratory viruses enter the body through the nose and throat. There the virus takes over some cells and uses them to make more viruses. When the cells release the virus particles into the circulation, other cells are taken over by the virus. In this way, the multiplication of the virus continues. The person recovers when the body's immune (defence) system develops a protection called antibodies to fight off the viral infection. Some infections can attack pregnant women from the intestines. These include viruses, parasites and germs carried in food.
Another route of infection is from the urinary and reproductive systems, often sexually transmitted diseases. Sometimes infections can spread upwards (ascending infections) from the vagina and infect either the membranes or the waters around the baby. This is called chorioamnionitis. Organisms can do this either on their own or as a mixed infection. The woman can go into preterm labour or the baby can be born with a serious infection like pneumonia. This is an area where ongoing research is changing our ideas.
Vertical transmission refers to when an infected woman passes on her infection to the baby. The baby can be infected directly from the mother's blood stream during pregnancy, during passage down the birth canal or shortly afterwards by contact such as breast feeding. To affect the fetus, an organism has to get to the cells in the placenta. It has to cross to the baby's side of the placenta and then it has to get into the baby's blood. Finally it has to infect the baby's cells. This complex process means that not all infections the mother has will result in infections in the baby.
When a baby is born with a medical condition due to an infection of pregnancy, it is called a congenital infection or syndrome.
Rubella is also known as German measles. The danger time for this infection is very early in pregnancy, sometimes before the woman realizes she is pregnant. With German measles the effect on the baby depends on which organs are developing at the time the infection occurs. The result may be deafness, heart disease, cataracts or abnormal brain development. Immunization programs in schools have resulted in a dramatic decrease in the number of infants born with congenital rubella syndrome but it still does occur.
Chickenpox is caused by the varicella zoster virus. Only a few women with this infection will have babies that are affected. If the baby is affected early in pregnancy, the most likely problem is poor limb development. Late in pregnancy, the only likely effect is some scarring of the baby's skin due to the chicken pox that occurred. Stillbirth and preterm labour are more likely if the mother becomes severely ill. A baby whose mother gets the infection close to the time of birth is at great risk in the newborn period.
This virus causes 'Fifth Disease' or 'Slapped Cheeks Disease.' Again only a small number of infected women will have infected babies. The earlier in pregnancy that infection happens, the more severe the effect on the baby. The virus destroys the baby's red blood cells but does not cause any physical deformity. If the pregnancy is severely affected, the woman could lose the baby or have a severely anemic baby. Expert care is now available to treat these babies while they are still in the womb. Sometimes the baby's immune system will develop enough so the baby can fight off the infection and recover completely.
Cytomegalovirus or CMV is the most common congenital infection. Most women are immune to CMV. However, the babies of those who do become infected in pregnancy will develop congenital CMV about half the time. These babies may appear to be normal at birth. Only later are they found to have hearing difficulty and other problems with brain development. There is no treatment or immunization available for this virus.
Toxoplasmosis is a parasite whose life cycle includes a phase in cats (cougars to kittens). It is found in cat urine and feces. It is also found in a wide variety of meat and even water, although rarely. Again the infection has to cross the placenta and then establish itself in the baby. The danger is present throughout pregnancy. The earlier in pregnancy it occurs, the more severe the effect on the baby. Fortunately, it is more likely for the baby to become infected when the illness occurs in late pregnancy so the effects are much milder. The effects only become apparent as a child gets older when blindness, deafness and delays in development are noted. It is very important to identify the babies with this congenital infection since treatment may prevent these long term problems.
Another infection from food that can attack pregnant women is listeria. Again this is a rare infection. In my town (population 35,000) I would expect there to be one case of listeria in pregnancy every 16 years. Listeria is a soil organism found widely in nature. Unfortunately, it is quite happy living and breeding in the temperatures found in a refrigerator. One danger seems to be when prepared vegetable foods such as coleslaw contaminate prepared meats and cold cuts. Delicatessens in supermarkets have been redesigned to avoid this possible contamination. Other sources of infection are raw (unpasteurized) milk and soft cheeses. The effect on the mother may be minimal or she may become septic (feverish and severely ill), go into preterm labour, miscarry or experience a stillbirth. Prevention is easy and accomplished by avoiding risky foods.
Syphilis is one of several sexually transmitted diseases (STDs) that can cross the placenta and cause congenital abnormalities such as facial deformity and altered brain development. Syphilis is treated with penicillin or other antibiotics. It is very, very rare due to routine blood tests and effective treatment. In over 20 years on Vancouver Island, I have only heard of one case of congenital syphilis.
Group B streptococcus can be picked up in late pregnancy or during childbirth and rarely causes life-threatening infection for the baby. The doctor will screen for Group B streptococcus in one of two ways. A swab may be taken from the vagina and anus at about 36 weeks and treatment with antibiotics started if Group B strep is found. The other way is to treat the mother during labour. This works very well to prevent most cases of this disease.
Only a few babies will pick up a herpes infection during birth. For those who do, it can result in severe brain damage. The greatest danger with herpes occurs in women who have a genital infection for the first time at the time of birth and are unaware of it. Those women with active herpes infection at the time of labour are offered a caesarean section delivery.
Hepatitis B is a viral infection that results in liver damage and is often spread by sexual contact or intravenous (IV) drug use. Hepatitis B is also passed on by vertical transmission when the mother carries this virus in her blood stream. If a woman has hepatitis B, her baby is vaccinated at birth and in the first six months of life. This prevents the development of the disease in the baby.
Sexual activity, IV drug use and vertical transmission also cause HIV infections and AIDS. This virus can cause a baby to be born too small or too early. Babies born with HIV have severe medical problems throughout their short lives. HIV can be prevented in most babies by treating the mother in pregnancy and at birth and treating the baby immediately after birth. Breast-feeding is not advised for mothers who are infected with HIV.
Chlamydia and gonorrhea can affect the baby's eyes. All babies are given antibiotic eye drops or ointment shortly after birth to prevent these infections. We do not yet have effective screening for other ascending infections. Provided a woman has a stable one-to-one relationship there is no evidence that sexual activity at any stage of pregnancy will introduce infection, cause miscarriages or trigger preterm labour in an otherwise healthy woman.
Small children are the reservoir for respiratory viruses. If you are pregnant, it is not practical to cut yourself off from your own children and those of your friends. It is, however, wise to avoid children who are obviously ill as much as possible.
Prevention starts before you become pregnant. Talk to your doctor about checking to learn which infections you are immune to. If there are some for which you are not immune, be immunized if that is available. There are public health immunization programs available for rubella and hepatitis B. It is hoped there will soon be a program for chickenpox as well since this vaccine is now available.
Screening blood tests at an early prenatal visit will identify mothers who have been infected with hepatitis B, syphilis or HIV. This allows time for the treatment of the mother and baby. If you have a cat, let your partner handle cat litter while you are pregnant to avoid exposure to toxoplasmosis.
Simple food handling rules will also protect you from listeria as well as toxoplasmosis:
Although it is unlikely your baby will develop a congenital infection, it is important to report unusual infections and rashes to your prenatal care provider. If you develop one of these infections, steps may be taken to reduce the risk for you and your baby.
Enjoy your pregnancy and have a healthy baby.