First Trimester Testing
Can Screening Detect All Birth Defects?
First trimester screening is not diagnostic, but it can be used to guide decision making. To determine whether the fetus has a chromosomal abnormality, amniocentesis or chorionic villus sampling (CVS) must be performed. These procedures carry a small risk of miscarriage and therefore have traditionally been recommended to women who are over 35 or who have a positive medical history.
How is First Trimester Screening Performed?
This screening requires a sonogram and maternal blood work performed between 11–14 weeks of pregnancy. The sonogram will confirm how far along your pregnancy is by measuring the fetal crown rump length (CRL). In addition, a measurement of the skin fold along the back of the baby's neck, called the nuchal translucency (NT), will be taken. A maternal blood sample is used to analyze two biochemical markers called free beta-human chorionic gonadotropin (hCG) and pregnancy associated plasma protein-A (PAPP-A), which are found in the blood of all pregnant women. In some pregnancies when the baby has Down syndrome or trisomy 18, there is extra fluid behind the baby's neck and the hCG and PAPP-A results are abnormal. Combining your age-related risk with the NT measurement and blood work provides a risk figure for Down syndrome and trisomy 18. The blood test and the NT measurement can detect approximately 83% of babies with Down Syndrome or Trisomy 18.
How Accurate is First Trimester Screening?
Because this is a screening test, a positive result (showing an increased risk) does not mean your baby has a problem, only 1 in 25 is a true positive. Further diagnostic tests are options for you to consider. Also, a negative or normal result (one that shows a decreased risk) does not mean the baby will not have Down syndrome or trisomy 18. The first trimester screen detects about 83% of pregnancies in which the baby has Down syndrome or trisomy 18. Finally, this screen is not designed to provide information about the possibility of other chromosomal conditions, nor about many other genetic syndromes, genetic disorders, birth defects, or causes of mental retardation.
What is the Integrated Screen?
The integrated screen combines the biochemical markers from the first screen, NT measurements, and a second trimester maternal serum screening test, also known as the “Quad screen”, to provide the highest detection rate for Down syndrome and Trisomy 18. This test requires two separate blood draws and a NT measurement; the results are combined into one risk assessment, reported only in the second trimester. The detection rate of the integrated screen is 92% for Down Syndrome, 90% for Trisomy 18. In addition, the alpha fetal protein (AFP) portion of the Quad screen can identify pregnancies at an increased risk for open neural tube defects such as spina bifida at a rate of 80%. The ability to detect open neural tube defects is not available with first trimester screening.
Who Should Consider Screening?
Screening tests should be offered to all pregnant women who are less than 35 years of age and who are at low risk for genetic abnormalities. The American College of Obstetricians and Gynecologists (ACOG) 2004 Position Paper acknowledges first-trimester screening as a viable option for women under 35 and those 35 and over who choose not to have invasive testing. ACOG continues to recommend chorionic villi sampling or amniocentesis for women who are 35 and over at delivery or high risk to accurately diagnose 99.9% of all chromosome abnormalities.
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Genetic / Preconceptual Consultation
What is Genetic Counseling?
Genetic counseling is the process by which a healthcare professional gathers and provides information about a real or potential genetic issue that may affect a current or future pregnancy. In our office, the physician, certified nurse-midwife or nurse practitioner provides this service. We also work closely with genetic counselors in the community and other parts of the country.
Who May Need Genetic Counseling?
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Any pregnant woman who will be 35 years or older at the time of delivery.
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Individuals who have a personal and/or family history of chromosomal anomaly, birth defect, or mental illness.
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Couples at risk for having a child with a genetic condition such as Tay Sachs disease, cystic fibrosis, or sickle cell disease/anemia.
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Couples with increased risk of Spina Bifida.
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Women who have had an abnormal AFP/Triple Screen/First Trimester Screen/Quad Screen, indicating an increased risk of Down’s Syndrome, trisomy 18 or neural tube defect.
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Patients with abnormal ultrasound findings.
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Individuals who have experienced two or more pregnancy losses.
What Happens During Counseling?
A healthcare provider will ask you to complete a genetic questionnaire. You will discuss your personal health history and your family history. The healthcare provider will explain the genetic issue and identify any genetic testing that may be available. They will provide you with community resources and very often, written information. Genetic counseling is non-directive, meaning the practice does not push for any particular resolution. This leaves the provider free to support the individual, couple, and/or family in their decisions regarding testing and pregnancy management.
What is Preconceptual Counseling?
Preconceptual counseling is the process by which a healthcare professional provides information about a real or potential health issue, prior to pregnancy.
Who May Need Preconceptual Counseling?
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Individuals who have experienced two or more pregnancy losses.
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Individuals who have a personal and/or family history of chromosomal anomaly, birth defect, or mental illness.
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Couples at risk for having a child with a genetic condition such as Tay Sachs disease, cystic fibrosis, or sickle cell disease/anemia.
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Couples with increased risk of Spina Bifida.
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Individuals with a history of chronic disease such as diabetes, sickle cell disease/anemia, Lupus, or other serious medical conditions.
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Individuals with exposure to harmful substances such as radiation, chemicals, drugs or alcohol.
What Happens During Counseling?
A healthcare provider will ask you to complete a genetic questionnaire. You will discuss your personal health history, social history, and family history. The healthcare professional will provide information regarding potential testing and/or health risks which may be involved with your pregnancy.
