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OB Genetics
| Question | Answer |
|---|---|
| Candidates for Prenatal Diagnosis Reasons for referral | AMA, Abnl screening results, fm hx of birth defect, chromosome condition or genetic dz, multiple pregnancy losses, maternal conditions, teratogens, consanguinity, ethnicity |
| Increased/Advanced maternal age | Mothers who will be 35 years or older on the day of delivery |
| 47, XX + 21 | Down Syndrome |
| ___ is the only thing that truly influences chromosomal changes | maternal age |
| Single gene conditions | ex: cystic fibrosis, sickle cell dz |
| Mulitfactorial conditions | ex: club foot, cleft lip, neural tube defect |
| Multiple pregnancy Losses | defined as 3 or more pregnancy losses. This is changing to 2 or more in women who are 35 or older |
| Maternal conditions that can influence birth defects and pregnancy complications | insulin dependent DM, Lupus (more miscarriages), seizure disorders, substance abuse |
| Teratogens: An exposure during embryogenesis which has a harmful effect on the developing fetus. Examples: | Maternal conditions, Medications (Valproic Acid, accutane), Excessive heat, hypoxia, Recreational drugs (ethanol, cocaine, tobacco) |
| Two systems that develop throughout pregnancy | brain and gonads. |
| Cosanguinity is more common in | Middle Eastern Countries |
| First trimester screening "Nuchal translucency Screening" | earlier option for patients who want risk assessment for Down's syndrome, Trisomy 13 & Trisomy 18. Ultrasound measurement obtained between 10-13 weeks of pregnancy. Biochemical screening: PAPP-A, hCG. Demographic information |
| Thicker Nuchal translucencies (greater than 3mm =60% risk of aneuploidy) have higher risk for | chromosome conditions, and cardiac malformations. Aneuploidy (abnl number of chromosomes) |
| sensitvity of Nuchal translucency test | 50-85% detection, 4.5% false positive. Combined with Biochemical screening: up to 80% detection of Down's, 90% detection of Tri 18 and Tri 13. |
| Limitations of First Trimester Screening | Accuracy of NT strongly dependent on experience of sonographer, not all women enter in time for screening, results may arrive too late for diagnostic testing, cost, cannot detect many NTD's or ventral wall defects (omphaloceles, gastrochisis) |
| CVS | Chorionic villi sampling; essentailly a biopsy of the placental tissue |
| When is CVS performed? | Between 10-12 weeks gestation. Prior can cause limb anomalies |
| CVS notes | Detects aneuploidy and single gene conditions. Cannot detect ONTDs or evaluate fetal anatomy. |
| Early Amniocentesis | Not common, usually done when person not qualified to do CVS. Lecturer does not offer. Performed between 12-14 wks gestation. Higher risk for miscarriage. |
| Second Trimester Screening | Maternal Serum Screening (AFP, Triple and Quad screens; provides biochemical screening and demographic info). Dection of neural tube defects (80%) and certain aneuploidies |
| AFP | increased with risk of neural tube defect. |
| Down Syndrome Screening | triple screen (AFP, hCG, uE3 detects 60%); quad screen (AFP, hCG, uE3, DIA detects 70%) |
| low AFP may mean | renal agenesis; AFP high - ventral wall defects |
| Disadvantages of Maternal Serum Screening | cannot r/o all aneuploidies, cannot eliminate risk for Down's, Trisomy 18 or NTDs, Increases anxiety especially is result is abnl |
| Ultrasound | can identify approximately 50% of babies with Down's Syndrome |
| US findings associated with aneuploidy | Hydrocephaly or other intracranial abnormalities, cystic hygroma, increased nuchal fold, hydrops, omphalocele, cardiac defects, kidney and bladder malformations, meningomyelocele, two-vessel umbilical cord |
| Omphalocele | a congenital malformation in which variable amounts of abdominal contents protrude into the base of the umbilical cord. As the fetus grows in pregnancy, the intestines grow and get longer & project from the abdomen into the cord. |
| Hydrops | Hydrops fetalis is a serious condition in which abnormal amounts of fluid build up in two or more body areas of a fetus or newborn |
| Gastrochisis | congenital fissure of the anterior abdominal wall |
| echogenic bowel | _______________. Associated with CMV, trisomy 21, cystic fibrosis, maternal/fetal bleed |
| Hypopolastic 5th digit is associated with | Down's syndrome |
| Traditional Amniocentesis | Performed weeks 15 through term. 1/200 risk for spontaneous abortion |
| Percutaneous Umbilical Blood Sampling (PUBS) | Performed after 16 wks gestation. US guidance. IM injection of pancuronium bromide to fetus or umbilicus. 1/100 risk for miscarriage. Not used much to obtain genetic info |
| Premimplantation Genetic Diagnosis (PGD) | Performed in conjunction IVF, allows embryos to be tested for genetic conditions or anueploidy in question. 30% of transferred embryos will implants. Expensive (upwards of 30K, many insurance copmanies do not cover) |
| Flourescent In situ hybridization (FISH) | Allows for a rapid, preliminary result of certain aneuploidy. Can identify conditions associated with small deletions of chromosomes(i.e., Prader-Willi syndrome) |
| Quad screen in Maternal Serum Screening does not impact the detection rate of | Trisomy 18. |
| The only protein which impacts the detection rate of Neural tube defects: | AFP |
| High AFP is associated with | Ventral wall defects |
| Low or undetectable AFP | renal agenesis |
Created by:
ltm12