What Genetic Screening is Needed in Pregnancy?
Frederick R. Jelovsek MD
Many pregnant women want to know whether their baby will be normal; some do not. They may not want to know because they are afraid of undergoing a diagnostic procedure such as amniocentesis. They may not want to know because it doesn't matter anyway, they wouldn't terminate a pregnancy if the baby was abnormal so why know and just worry about it? Physicians like to know in case there is something wrong that might be made worse with a vaginal delivery such as a neural tube defect, hydrocephalalus or brittle bones in the baby's head called ostogenesis imperfecta. For certain conditions, physicians would like to have specialists on hand right at the time of delivery if the baby had a diaphragmatic hernia (bowels up in the chest cavity) or gastroschisis (bowels outside abdominal cavity on skin) or even certain heart defects.
The problem with genetic diagnosis is that each birth defect is fairly rare so a significant amount of money is spent in trying to diagnose a specific anomaly. All of the screening tests have a moderate number of false positives that cause major anxiety among those women who screened as possibly positive but didn't end up having a baby with that anomaly. Ultrasound exams can routinely miss up to 50% of anomalies although most of the ones missed are the more minor ones. The question remains, what strategy should be used to determine if a woman is at high risk for a baby with a specific birth anomaly.
A recent medical educational article, Dugoff L: Genetic screening of gravidas: What is called for today? OBG Mangement 1998;Sept:54-64, identified 12 key questions that can identify an increased risk:
Genetic Screening Questions
| Age 35 or older | After age 35, the incidence of chromosomal anomalies detectable by amniocentesis exceeds the pregnancy loss rate from the procedure itself |
| Ethnic origin of each parent | Certain conditions are much more frequent in individuals of certain ethnic background. Ashkenazi Jews have a higher incidence (1 in 3600) of Tay-Sachs disease as do French Canadians and people of Cajun descent. Sickle cell anemia and other hemoglobinopathies are more common among individuals of African, Mediterranean, Middle Eastern, Carribean, Latin American or Indian descent. |
| Family history of Down syndrome or other chromosome anomaly | Some chromosomal anomalies are spontaneous occuring but many are inheritable and should be investigated. |
| Family history of mental retardation (and cause) | Down syndrome and Fragile X syndrome are 2 conditions that cause mental retardation. Chromosomal anomalies only account for about 35-40% of mental retardation. |
| Family history of genetic conditons for which testing is available | There are prenatal tests available for Tay-Sachs disease, cystic fibrosis, Down syndrome, thalassemia, Sickle cell disease among the many possible genetic problems. |
| Family history of defects which can be picked up by ultrasound | Congenital heart problems, polycystic kidney, Potter's syndrome, and other conditions that are inheritable can be detected by ultrasound. Some more minor anomalies such as club foot, cleft lip or palate and some heart defects are frequently missed on ultrasound exam. |
| History of previous stillbirth, recurrent miscarriages or 2nd trimester fetal death | These conditions can be associated with certain chromosomal anomalies such as all trisomies, Potter's syndrome (missing or undeveloped kidneys) |
| Are parents related to each other | Any relationship closer than second cousins presents a higher risk of birth defects. |
| Does mother have history of diabetes, phenlyketonuria or epilepsy | These conditions can lead to birth defects which can be assessed prior to the babies birth. |
| Does either parent have a history of vascular clotting | Hereditable hemoglobinopathies and other conditions can manifest mainly as vascular clotting or thrombosis. |
| Taken any prescribed or OTC medicines or supplements since became pregnant | Certain antibiotics, anti-convulsant medications, blood thinners, hormones and steroids, anti-cancer agents and other agents can cause birth defects. |
| Consumed alcohol or recreational/street drugs since pregnancy start | Fetal alchohol syndrome is caused not only by alcohol, but other sedatives and street drugs can cause similar changes. |
For a sample of genetic testing for syndromes other than just chomosomal
number abnormalities such as Down syndrome, see a sample lab offering:
Celtek genetic testing
| Other Related Articles |
Ultrasound Can Miss Fetal Anomalies Can Ultrasound Detect Down Syndrome? |
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