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Individual differences |
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Advanced Maternal Age - Amniocentesis
- Welcome and acknowledge any prior phone contact.
- Discuss the reason for referral. Do they understand why they were sent to genetics?
- Assess their concerns and what they hope to gain from the session.
- Assess their degree of knowledge about genetics, heredity, AMA, etc.
- Provide overview of the session and discussion topics.
- Obtain client and partner information (age, occupation, ethnicity, religion, consanguinity, health)
- Elicit family history and construct pedigree.
- Pregnancy history (dates, procedures, exposures, complications)
- Discuss population pregnancy information - every pregnancy has a 3-5% risk for congenital malformations; every pregnancy has a 2-3% risk of miscarriage.
What is AMA?Edit
- Advanced maternal age applies to anyone aged 35 years or above at the expected date of delivery.
- As maternal age increases, the risk of birth defects (particularly chromosomal abnormalities) increases.
- Age 35 is the cutoff for AMA because this is the point where the procedural risk equals the risk of aneuploidy.
What are chromosomal abnormalities?Edit
- Explanation of chromosomes.
- Explanation of meiosis, haploid germ cells, fertilization to a diploid zygote.
- Explanation of non-disjunction. Focus on how women are born with all their eggs and they mature with age.
- Discuss common trisomies/monosomies (13, 18, 21, 47XXY, 45X), show karotypes, and give general description of clinical features and prognoses.
- Discuss client's age-related mid-trimester risks for any chromosomal abnormalities and for Down syndrome in particular.
- Record data on intake.
What are the testing options?Edit
- Triple Marker Screening:
- Maternal blood test performed at 15-22 weeks.
- Screening test only, NOT diagnostic.
- Indirect measurement of fetal AFP, hCG, uE3 production.
- Detects approx. 85% NTDs, up to 85-90% of DS, and up to 80% of Trisomy 18 in women with AMA.
- False-positive rate of 25% in women over 35 years of age.
- Does not detect all chromosomal abnormalities assoc. with AMA
- Can detect many major birth defects.
- Some fetuses with chromosomal abnormalities have characteristics that can be seen by ultrasound as "markers", but others have no visible anomalies.
- Ultrasound can NOT diagnose chromosome abnormalities.
- Medical procedure that removes a small sample of amniotic fluid (made of fetal urine, contains fetal skin cells) from the amniotic sac surrounding the fetus.
- Usually performed between 15-18 weeks (although some labs will interpret data from 13.5 to 21 weeks)
- Fluid is used for genetic analysis - fetal karyotyping, biochemical studies, DNA studies, alpha-fetoprotein and acetyl cholinesterase measurements.
- Procedure takes 20-45 minutes (1-2 minutes for needle insertion).
- May be required to have a full bladder.
- Lie down on back with hands folded behind your head.
- Abdomen cleansed with betadeine.
- Local anesthetic (xylocaine) may be used to numb the outer layer of skin - this may feel like a pin prick followed by a stinging or burning sensation.
- Ultrasound is used to locate the fetus and placenta, identify the pocket of fluid, and guide the needle.
- Physician inserts the needle (22 gauge with a stylet) through the abdomen and into the uterus - some discomfort may be felt when the needle enters the skin and then the uterus (may feel like a menstrual cramp); a sharp pain lasting a few seconds may be felt when the needle enters the amniotic sac.
- Stylet is removed and the first few cc of fluid are discarded due to possible maternal cell contamination. About 20 cc (1 tablespoon) of amniotic fluid is removed - may feel pressure in the lower abdomen when the fluid is withdrawn; is quickly replaced by the fetus.
- Needle is removed, bandage applied, fetal heart activity is monitored by ultrasound, no overnight hospital stay.
- Fluid is sent to lab and results are available in 1-2 weeks. Discuss how results will be received.
- About 95% of women receive a negative result.
- Total cost is $600-$900.
- Afterwards, no strenuous activity for 24 hours. Follow up with MSAFP at 16-18 weeks and ultrasound at 18-20 weeks.
Benefits of AmnioEdit
- Accuracy of karyotype is >99% (NTD detection is about 90-96%).
- Can detect chromosomal abnormalities (aneuploidies).
- Can detect neural tube defects (spina bifida, anencephaly).
- Tells the sex of the fetus.
Limitations of AmnioEdit
- Does not detect all possible birth defects (only about 10% of 400 known congenital malformations).
- Cannot predict the severity of the defect/disorder.
- If first procedure fails, a second may be attempted that same day. If it doesn't work, then additional procedures should be postponed for 3-7 days.
- Cell culture failure could occur (rare, <1%).
Risks Associated with AmnioEdit
- Risk of miscarriage - 1/200 (0.5% beyond background risk).
- Rh (-) mothers must be given RhoGam in order to prevent blood group sensitization.
- Uterine cramping is not uncommon.
- Notify your doctor is you have transient spotting or leakage of amniotic fluid (2-3% of cases).
- Very rare chance of infection to uterus, hemorrhage, or maternal death.
- Risk of birth defects due to amnio is remote (risk of clubfoot increased during early amnio).
- Discuss psychosocial issues that may arise.
- Remind that no decision has to be made today.
- Review and summarize.
- Answer final questions and concerns.
- Give out patient resources.
The information in this outline was last updated in 2001.
Material obtained under GFDL Licence from http://en.wikibooks.org/wiki/Handbook_of_Genetic_Counseling