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
|
