Pregnancy and congenital infection
CMV (cytomegalovirus) forms part of the association known as TORCH infections that lead to congenital abnormalities. These include Toxoplasmosis, Rubella, Herpes simplex, as well as CMV, among others.
The incidence of primary CMV infection in pregnant women in the United States varies from 1% to 3%. Healthy pregnant women are not at special risk for disease from CMV infection. When infected with CMV, most women have no symptoms and very few have a disease resembling mononucleosis. It is their developing fetuses that may be at risk for congenital CMV disease. CMV remains the most important cause of congenital viral infection in the United States. CMV is the most common cause of congenital infection in humans.However, these risks appear to be almost exclusively associated with women who previously have not been infected with CMV and who are having their first infection with the virus during pregnancy. Even in this case, two-thirds of the infants will not become infected, and only 10% to 15% of the remaining third will have symptoms at the time of birth. There appears to be little risk of CMV-related complications for women who have been infected at least 6 months prior to conception. For this group, which makes up 50% to 80% of the women of child-bearing age, the rate of newborn CMV infection is 1%, and these infants appear to have no significant illness or abnormalities.
The virus can also be transmitted to the infant at delivery from contact with genital secretions or later in infancy through breast milk. However, these infections usually result in little or no clinical illness in the infant.
For infants who are infected by their mothers before birth, two potential adverse scenarios exist:
- Generalized infection may occur in the infant, and can cause complications such as low birth weight, microcephaly, seizures, petechial rash similar to the "blueberry muffin" rash of congenital rubella syndrome, and moderate hepatosplenomegaly (with jaundice). Though severe cases can be fatal, with supportive treatment most infants with CMV disease will survive. However, from 80% to 90% will have complications within the first few years of life that may include hearing loss, vision impairment, and varying degrees of mental retardation.
- Another 5% to 10% of infants who are infected but without symptoms at birth will subsequently have varying degrees of hearing and mental or coordination problems.
To summarize, during a pregnancy when a woman who has never had CMV infection becomes infected with CMV, there is a potential risk that after birth the infant may have CMV-related complications, the most common of which are associated with hearing loss, visual impairment, or diminished mental and motor capabilities. On the other hand, infants and children who acquire CMV after birth have few, if any, symptoms or complications.
Recommendations for pregnant women with regard to CMV infection:
- Throughout the pregnancy, practice good personal hygiene, especially handwashing with soap and water, after contact with diapers or oral secretions (particularly with a child who is in day care).
- Women who develop a mononucleosis-like illness during pregnancy should be evaluated for CMV infection and counseled about the possible risks to the unborn child.
- Laboratory testing for antibody to CMV can be performed to determine if a women has already had CMV infection.
- Recovery of CMV from the cervix or urine of women at or before the time of delivery does not warrant a cesarean section.
- The demonstrated benefits of breast-feeding outweigh the minimal risk of acquiring CMV from the breast-feeding mother.
- There is no need to either screen for CMV or exclude CMV-excreting children from schools or institutions because the virus is frequently found in many healthy children and adults.
Toxoplasmosis is caused by a parasite called toxoplasma gondii. This is found in different forms in raw meat, within cats that eat raw meat and their faeces. Toxoplasmosis infection is common in both men and women outside of pregnancy, however it is infection during pregnancy that is of most concern as it can lead to infection in the unborn infant: congenital toxoplasmosis. Once you have had toxoplasma infection, the bodies immunity will prevent you catching it again (IgG positive). Around 30% of women will have already had a toxoplasma infection before pregnancy. It typically causes a flu-like illness with swollen glands in the neck. Most people are unaware that it was in fact toxoplasmosis. It is not known for sure how many women catch toxoplasmosis during pregnancy (IgM and IgA positive too), but some research suggests it is of the order 2 in every 1000, which means about 1400 each year in the UK.
In only about 30-40% of women who catch toxoplasmosis during pregnancy, does the infection pass to the unborn baby. The actual risk appears to be related to the gestation at which it is acquired. It is greatest in the third trimester at 70%, whereas in early pregnancy only 15% of infants will become infected. Toxoplasmosis infection may lead to miscarriage, stillbirth, or survival with growth problems, blindness, water on the brain (hydrocephalus), brain damage, epilepsy, or deafness. If a woman is found to have acquired toxoplasmosis during pregnancy, she will be offered an ultrasound scan to look for signs of fetal infection. After 20 weeks gestation, she may be offered a definitive test - cordocentesis. This involves a scan and blood sample being taken from the umbilical cord.
Although toxoplasmosis is quite serious when it occurs, as you will see from the figures above, it is relatively rare. Women with cats do not need to get rid of them when they become pregnant; it is just necessary to take a few precautions. Be sure to only eat meat that has been cooked right through. Wash your hands, cooking utensils and food surfaces after preparing raw meat and wash all the soil from fruit and vegetables before eating. Keep raw meat and cooked foods on separate plates. If possible get someone else to clean out the dirty cat litter or use gloves and wash your hands afterwards. Always use gloves when gardening and wash your hands afterwards.
Herpes infections affect about 10% of the UK population, though only in one third of cases is an actual diagnosis as such made. It usually presents initially with a flu-like illness, followed by an outbreak of vulval sores, which are very painful and swollen glands in the groin. By a week to 10 days later these have usually healed over. Sometimes the initial attack is mistaken for a thrush infection, just causing an itch or soreness, seemingly responding to cream or pessaries. Occasionally it is completely without symptoms at all. The first (primary) attack is usually the most painful. The herpes virus stays in the nerve in the spine and can reactivate causing a secondary attack. This occurs on average at 3-4 months after the first one, and recurrences return on average 2-3 times per year, but this is extremely variable.
The risk of herpes to pregnancy is greatest if the primary attack occurs after 28 weeks. The mother's initial antibody response can take up to 12 weeks to fully develop. Secondary attacks are much less of a risk. The risk of herpes is passing the infection to the baby at the time of delivery. Primary attacks also can lead to early labour or poor growth. Because of these risks, a caesarean section is usually advised at term if a primary attack occurs during pregnancy after 28 weeks, or if there is an active secondary attack at the time of labour.
Parvovirus B19 Fifth disease, also known as erythema infectiosum, is a viral illness caused by human parvovirus B19. The term "fifth disease" refers to the fifth of the 6 rash-associated diseases of childhood.
Symptoms
Parvovirus B19 commonly causes a "slapped-cheek" rash on the face and, less commonly, fever, headaches, sore throat and joint pain. In adults, it may cause arthralgias (painful joints) in addition to the characteristic skin rash. These symptoms are more common in adult women than in men. They usually last for 2-4 weeks but may persist for months.
In some cases fifth disease can cause anemia. In healthy individuals, this anemia is mild and only lasts a short period of time.
Many people with fifth disease show no symptoms at all. Therefore, the only way to definitively diagnose it is to have a test. Approximately 50-60% of adults have had the disease and are immune. However, those who are not immune may be at risk from picking up this infection, particularly healthcare providers, childcare providers and teachers.
Transmission
Fifth disease is transmitted primarily by respiratory secretions (saliva, mucous etc.) but can also be spread by contact with infected blood. The incubation period (the time between the initial infection and the onset of symptoms) is usually between 4 and 21 days. Individuals with fifth disease are most infectious before the onset of symptoms. Typically, school children, day-care workers, teachers and mothers are most likely to be exposed to the virus. When symptoms are evident, there is little risk of transmission; therefore, infected individuals need not be isolated.
Hydrops fetalis.
Parvovirus infection in pregnant women is associated with hydrops fetalis due to severe fetal anemia, sometimes leading to miscarriage or stillbirth. The risk of fetal loss is about 10% if infection occurs before pregnancy week 20 (esp. between weeks 14-20), but minimal after then. Routine screening of the antenatal sample would enable the pregnant mother to determine the risk of infection. Knowledge of her status would allow the mother to avoid the risk of infection.The risk to the fetus will be reduced with correct diagnosis of the anemia (by ultrasound scans) and treatment (by blood transfusions). There is no evidence to suggest that Parvovirus B19 leads to developmental abnormalities in childhood.
Chicken Pox (Varicella) It's not uncommon for women who are pregnant to come into contact with someone who has chicken pox. This can cause great worry, but it is uncommon for there to be a problem.
Firstly, if you have definitely had chicken pox before, there is no risk to the baby. In any case, even if you don't recall having had chicken pox, it is likely you have antibodies (80% do) from a silent infection. So if there's any doubt about it, you should see a doctor for a blood test to check for immunity. Sometimes the laboratory can use the stored blood taken at booking to speed this up.
Risks to the baby are important at the following two times, only if mum gets chicken pox:
1. Before 20 weeks - risk of chicken-pox syndrome. This is actually quite rare. Up until 14 weeks the risk is about 0.4%, whereas between 14-20 weeks it is 2%. If a woman has VZ-Ig treatment (see below) after being exposed, the risk is even lower.
2. Mum's rash developing within a week before delivery to a month afterwards. It takes about a week for mum to pass the protective antibodies to the baby, so if born before that time, the baby is at risk of overwhelming infection after birth.
Between 20 weeks and term there is no risk to the baby.
VZ-Ig is a form of antibody treatment that can reduce the risk of chicken-pox syndrome and should be given by 10 days after the initial attack.
Vaginal Infections
Thrush Pregnancy makes a woman more likely to get a thrush infection, most commonly caused by the yeast Candida albicans. This yeast is commonly found in the vagina in up to 16% of non-pregnant women and 32% during pregnancy. It does not always cause symptoms and only requires treatment if it causes troublesome itching, soreness or the typical thick, white discharge. It is more common in second and subsequent pregnancies, in the third trimester , during summer months, following a course of antibiotics and in diabetic women. Treatment with Clotrimazole (Canesten) vaginal suppositories is usually effective. The tablet treatment Fluconazole (Diflucan) is not advised during pregnancy.
Men can be affected by thrush, it causing a redness and soreness of the glans of the penis, with a pin-point spotty appearance. Thrush affecting men is a lot less common than for women and it is even less frequent for a man to act as a 'reservior' of infection where the woman keeps getting it back from him. It is not necessary for your partner to get treatment unless they have symptoms.
Group B Streptococcus (GBS) Group B streptococcus is a bacterium that around 15-20% of pregnant women carry in the vagina, usually causing no problems at all. In a small number of cases, the bug is passed to the baby during delivery and it can lead to a blood-borne infection or even meningitis. This condition affects only 3 per 10,000 babies in the UK. The incidence is much higher in the US, and Hungary so they have developed a comprehensive screening program for GBS at the 36th weeks of pregnancy. The mother infected with GBS should be treated during delivery to avoid contact infections of the newborn baby.
In the UK treatment is usually only advised in one of a number of 'high risk' scenarios. These include: early labour (before 37 weeks), prolonged or early rupture of the membranes, if there is a temperature during labour or if a previous baby has been affected with the condition. The treatment involves antibiotics through a drip during labour - tablet treatment cannot reliably eradicate the infection.
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Testing for Down Syndrome
Introduction
We already know that as the mother's age advances, the risk of having a baby with Down syndrome increases. Because the risk of having a baby with Down syndrome rose above the 1 in 250 mark at the 35th birthday for women, it had become the standard of care to offer the screen for Down syndrome to all mothers 35 years and older. At the beginning of 2007, the American College of Obstetricians and Gynecologists stated that all women regardless of age should be offered the opportunity for screening.
Over the last two decades, the screening was done between the 15th and 20th week of gestation, but it was most accurate between the 16th week and the 18th week. However, research in the last 6 years has concentrated on finding a way to screen in the first trimester to enable parents to have time to make choices when given the results of a positive screen test. The first trimester screen (11-13 weeks of pregnancy) now uses a combination of the maternal age, the serum screen (PAPP-A and BHCG) and an ultrasound measurement of nuchal transluceny (thickness of fluid at the neck) and nasal bone. When used correctly, this first trimester screen has a detection rate of approximately 95% of all cases of Down syndrome, with a false-positive rate of 5
Over the last 20 years, new technology has improved the methods of detection of fetal abnormalities, including Down syndrome. While there are ways to diagnose Down syndrome by obtaining fetal tissue samples by amniocentesis or chorionic villus sampling, it would not be appropriate to examine every pregnancy this way. Besides greatly increasing the cost of medical care, these methods do carry a slight amount of risk to the fetus. So screening tests have been developed to try to identify those pregnancies at "high risk." These pregnancies are then candidates for further diagnostic testing.
What is the difference between a screening test and a diagnostic test? In diagnostic tests, a positive result very likely means the patient has the disease or condition of concern. In screening tests, the goal is to estimate the risk of the patient having the disease or condition. Diagnostic tests tend to be more expensive and require an elaborate procedure; screening tests are quick and easy to do. However, screening tests have more chances of being wrong: there are "false-positives" or "screen-positives" (test states the patient has the condition when the patient really doesn't) and "false-negatives" (patient has the condition but the test states he/she doesn't).
Maternal Serum Screening
The mother's blood is checked for a combination of different markers: alpha-fetoprotein (AFP), unconjugated estriol (uE3), and human chorionic gonadotropin (hCG) make up the standard tests, known together as the "triple test." Sometimes a marker called inhibin A is added, making the "quadruple screen." These tests are independent measurements, and when taken along with the maternal age (discussed below), can calculate the risk of having a baby with Down syndrome. Over the last fifteen years, these were done in the 15th to 18th week of pregnancy. Recently, another marker called PAPP-A and human chorionic gonadotropin (hCG) was found to be of use even earlier at the 11-13 weeks of pregnancy with combination of an ultrasound scan (nuchal translucency and nasal bone measurement. see below).
- Alpha-fetoprotein is made in the part of the womb called the yolk sac and in the fetal liver, and some amount of AFP gets into the mother's blood. In neural tube defects, the skin of the fetus is not intact and so larger amounts of AFP is measured in the mother's blood. In Down syndrome, the AFP is decreased in the mother's blood, presumably because the yolk sac and fetus are smaller than usual.
- Estriol is a hormone produced by the placenta, using ingredients made by the fetal liver and adrenal gland. Estriol is decreased in the Down syndrome pregnancy. This test may not be included in all screens, depending on the laboratory.
- Human chorionic gonadotropin (BHCG) hormone is produced by the placenta, and is used to test for the presence of pregnancy. A specific smaller part of the hormone, called the beta subunit, is increased in Down syndrome pregnancies.
- Inhibin A is a protein secreted by the ovary, and is designed to inhibit the production of the hormone FSH by the pituitary gland. The level of inhibin A is increased in the blood of mothers of fetuses with Down syndrome.
- PAPP-A, which stands for pregnancy-associated plasma protein A, is produced by the covering of the newly fertilized egg. In the first trimester, low levels of this protein are seen in Down syndrome pregnancies.
A very important consideration in the screening test is the age of the fetus (gestational age). The correct analysis of the different components depends on knowing the gestational age precisely. The best way to determine that is by ultrasound.
Once the blood test results are determined, a risk factor is calculated based on the "normal" blood tests for the testing laboratory. The average of normals is called the "population median." Test results are sometimes reported to doctors as "Multiples of the Median (MoM)." The "average" value is therefore called 1.0 MoM. Down syndrome pregnancies have lower levels of AFP and estriol, so their levels would be below the average, and therefore less than 1.0 MOM. Likewise, hCG in a Down syndrome pregnancy would be greater than 1.0 MoM. In the serum screening, the lab reports all results in either this way or as a total risk factor calculated by a software program.
Calculating the Risk
In the 1980s and 90s, the results of the prenatal tests were expressed to parents as "high risk" and "low risk," depending on whether the risk result was above or below an arbitrary cutoff point at 1 in 250. (I have seen the cutoff as low as 1 in 200 and as high as 1 in 270.) The reason for choosing that cutoff value was based on the risk of complications from an amniocentesis procedure. If the mother's risk was less than 1 in 250 of having a child with Down syndrome, then the risk of amniocentesis was greater and the mother was called "low risk." Likewise, if the mother's results showed a greater risk than 1 in 250, the pregnancy was called "high risk."
Recently, however, the American College of Obstetricians and Gynecologists ("ACOG") have advocated not using the terms "high risk" and "low risk," but instead presenting the parents with the actual numerical risk value.
Ultrasound Screening
The main usefulness of ultrasound (also called sonography) is to confirm the gestational age of the fetus (it's more accurate than dating from the mother's last menstrual cycle). Another benefit of the ultrasound can also pick up problems of a serious medical nature, such as blockage of the small intestine or heart defects. Knowing these defects exist as early as possible will benefit the treatment of the child after birth.
Studies in the mid-1990s showed that there was a strong association between the size of a collection of fluid at the fetal neck, called nuchal transluceny, and the risk of Down syndrome. Early attempts to use a measurement of the nuchal area were limited by a wide variety in measurement techniques. Recently, standardized guidelines on measuring nuchal translucency along with specific training and certifications have been instituted, making this ultrasound measurement useful as part of the first trimester screen. There are now computer programs that can use this measurement to help calculate the risk of having a baby with Down syndrome.
Amniocentesis
This procedure is used to collect amniotic fluid, the liquid that is in the womb. It's performed in the doctor's office or in the hospital on an "out-patient" basis. A needle is inserted through the mother's abdominal wall into the uterus, using ultrasound to guide the needle. Approximately one ounce of fluid is taken for testing. This fluid contains fetal cells that can be examined for chromosome tests. It takes about 2 weeks to determine if the fetus has Down syndrome or not.
There is a slight increase in the risk of miscarriage: the normal rate of miscarriage at this time of pregnancy is 2 to 3%, and amniocentesis increases that risk by an additional 1/2 to 1%. Amniocentesis is not recommended before the 14th week of pregnancy due to a higher risk of complications and loss of pregnancy.
Which mothers should have an amniocentesis? The current recommendations by professional obstetric groups is that women with a risk of having a child with Down syndrome of 1 in 250 or greater should be offered amniocentesis.
Chorionic Villus Sampling (CVS)
In this procedure, instead of amniotic fluid being taken, a small amount of tissue is taken from the young placenta (also called the chorionic layer). These cells contain the fetal chromosomes that can be tested for Down syndrome. The cells can be collected the same way as the amniocentesis, but another method is to insert a tube into the uterus through the vagina. The method depends on the mother's anatomy.
CVS is usually carried out between the 11th and 14th weeks of pregnancy. Side effects to the mother are the same as with amniocentesis. The risk of miscarriage after CVS is slightly higher than with amniocentesis, increasing the normal risk of miscarriage to 3 to 4%. Studies have shown that the more experienced the doctor performing the CVS, the less the miscarriage rate.
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