What is Genetic Counseling?
Genetic counseling is a communication process that has at its goal, the alleviation of human suffering associated with the occurrence, or risk of occurrence, of a genetic disorder in a family. The counseling tries to achieve this goal by helping the counselee to:
- Comprehend the medical facts, including the diagnosis, probable course of the disorder, and the available management
- Appreciate the way heredity and environment contribute to the disorder, and the risk of recurrence in specified relatives
- Understand the alternatives for dealing with the risk of recurrence
- Choose the option which seems appropriate in view of their risks and their values, and act in accordance with the decision
- Make an optimal adjustment to the disorder in an affected family member and/or to the risk of recurrence of that disorder
Common Genetic Tests
This two part screen offers high detection rates, early answers and a low false positive rate for Down Syndrome, trisomy 18 (a rare but severe chromosome problem) and the open neural tube defect (spina bifida). The first part of the screen is performed between 11 weeks and 13 weeks, 6 days of pregnancy and involves a fetal sonogram to measure the size of the baby's neck (nuchal translucency). Also at this time blood is taken from the mother to measure two proteins, PAPP-A and HCG. The fetal neck measurement and proteins combined can provide an early screen for Down syndrome and trisomy 18. If these results are normal, a second sample of blood is taken from the mother between 15 and 21 weeks 6 days of pregnancy to measure four additional fetal proteins. The first and second parts of the sequential screen are combined to provide a detection rate for Down syndrome and trisomy 18 at 90%, with an open neural tube detection rate of 80%. If either the first of combined results are abnormal, diagnostic testing such as chorionic villi sampling (CVS) or amniocentesis can be considered.
Maternal Serum AFP Screening for Open Neural Tube Defects
Maternal serum alpha-fetoprotein testing (MSAFP) is a blood test which is offered as a part of routine obstetrical care. This screening test checks alpha-fetoprotein levels in the mother's blood. Elevated levels of MSAFP can be associated with fetal anomalies, such as spina bifida and abdominal wall defects. However, elevated MSAFP results are not always associated with fetal anomalies. If MSAFP is abnormally high, a repeat test is offered. If a repeat MSAFP is elevated, additional tests such as detailed ultrasound evaluation and genetic amniocentesis may be recommended.
Maternal Serum Quadruple Screening
Maternal serum quadruple screening for Down syndrome checks levels of alpha-fetoprotein and unconjugated estriol (made by the baby), human chorionic gonadotropin and dimeric inhibin-A (made by the placenta). These substances cross into the mother's bloodstream. Abnormal levels of these substances may indicate an increased risk for fetal Down syndrome. Babies with Down syndrome have three copies of chromosome 21 in each of their cells instead of two (the usual number). Babies with Down syndrome have developmental disabilities and a variety of birth defects. If quadruple screening reveals an increased risk for Down syndrome, detailed ultrasound evaluation and the option of genetic amniocentesis may be recommended.
Non-invasive Prenatal Testing (NIPT)
Non-invasive Prenatal Testing (NIPT) is a screening test, carried out on a maternal blood sample, which can be performed on women at or after 10 weeks' gestation to help identify fetuses at risk for Down syndrome (trisomy 21), trisomy 18 and trisomy 13. NIPT can also tell the gender of the baby and can identify sex chromosome abnormalities, such as Turner syndrome and Klinefelter syndrome. The detection rates for trisomy 21, trisomy 18, and trisomy 13 are up to 99%. The detection rate for Turner syndrome and Klinefelter syndrome is at least 95%. Testing is limited to the chromosomes and conditions listed above. This test will not identify other abnormalities of those chromosomes and does not detect abnormalities of other chromosomes not tested.
At the present time, per ACOG recommendations, NIPT is only being offered to women at increased risk for the conditions listed above. This includes women who will be 35 years or older at the time of delivery, women who have had an abnormal serum screening test (such as abnormal sequential screening or quadruple marker screening), women who have an abnormal prenatal sonogram with findings suggestive of a fetal chromosome abnormality, parental balanced Robertsonian translocation with increased risk of fetal trisomy 13 or trisomy 21, or women who have had a prior pregnancy affected with one of the chromosome abnormalities listed above. NIPT is a highly accurate screening test, but is not intended to replace diagnostic prenatal testing. Patients with a high-risk result should be referred for genetic counseling and be offered a fetal karyotype by chorionic villus sampling (CVS) or amniocentesis. Non-invasive Prenatal Testing does not screen for fetal open neural tube defects. A second trimester blood test called maternal serum alpha fetoprotein screening (MSAFP screening) is available to screen for open neural tube defects.
Chorionic Villus Sampling (CVS)
CVS is performed from 1013 weeks of pregnancy. It is a technique for removing a small piece of the developing placenta from within the uterus. Because the placenta and the fetus are genetically the same the placental tissue provides a reliable source of material for performing genetic testing. Due to the small risk of pregnancy complications associated with chorionic villus sampling, genetic counseling prior to this procedure is recommended.
Amniocentesis, usually carried out between 16 and 20 weeks of pregnancy, is a procedure which allows a pregnancy to be tested for certain kinds of birth defects. During an amniocentesis procedure, the physician uses ultrasound imaging to guide a thin needle into the amniotic sac and withdraws a small amount of fluid (approximately two tablespoons). The fluid is sent for testing to detect specific disorders such as chromosomal abnormalities and open neural tube defects. Deciding whether or not to have amniocentesis depends on the patient's special risks and concerns. Due to the small risk of pregnancy complications associated with amniocentesis, genetic counseling prior to the procedure is recommended.
Cystic Fibrosis Carrier Screening
Cystic fibrosis (CF) is one of the most common recessive genetic disorders in Caucasians of Northern European descent, affecting approximately 1 in 2500 newborns. Cystic fibrosis causes the body to produce abnormally thick mucous secretions, which prevent the normal functioning of a number of organ systems, most notably the respiratory and digestive systems. Approximately 4% of Caucasians of Northern European descent carry one abnormal CF gene. If both parents are CF carriers, each of their offspring will have a 25% chance to be affected with cystic fibrosis. Genetic testing on a blood sample can detect approximately 97% of CF carriers among Ashkenazi Jews and 90% of CF carriers in the Northern European Caucasian population. The carrier detection rate is slightly lower in other ethnic groups. If carrier testing shows that both parents are carriers, prenatal diagnosis for cystic fibrosis may be available.
Indications for Referral for Preconception or Prenatal Genetic Services
- Advanced maternal age (35 years or older at delivery)
- Abnormal maternal serum marker screening results
- Fetal anomalies noted on ultrasound evaluation
- Multiple pregnancy losses (equal or greater than two) and/or stillbirths
- Either parent or other family member with a chromosomal rearrangement
- Previous child or family history of chromosomal abnormality
- Either parent or child with a known or suspected inborn error of metabolism
- Parent or child with a known hereditary/genetic disorder
- Either parent or child with history of a structural abnormality (such as neural tube defect, cleft lip and palate, or congenital heart defect)
- Family history of mental retardation or developmental disabilities
- Member of an at-risk ethnic or racial group for which carrier testing and/or prenatal diagnosis may be available
Genetic Counselors at the Regional Perinatal Center
Tanya McGuire, MS
Ms. McGuire has been a Genetic Counselor at the Perinatal Center since 1994. Prior to obtaining her Master's of Science degree in Genetic Counseling, she worked in the Cytogenetics Laboratory at Upstate Medical University in Syracuse. She is a member of the National Society of Genetic Counselors, Inc.
Lindsey Guzewicz, MS
Ms. Guzewicz has been a Genetic Counselor at the Perinatal Center since June, 2020. She received her Masters Degree in Genetic Counseling from the University of Colorado Anschutz Medical Campus in May 2020. She is a certified Genetic Counselor by the American Board of Genetic Counseling. She is a member of the National Society of Genetic Counselors. Inc.