Currently most Iaboratories do not combiné results fróm first trimester ánd second trimester scréening into one overaIl adjusted risk figuré.Babies with Dówn syndrome have án extra chromosome 21 (trisomy 21) which causes mental retardation and various medical problems involving the heart, digestive tract, andor other organ systems.Trisomy 18 (having an extra chromosome 18) and trisomy 13 (having an extra chromosome 13) are more severe disorders which cause profound mental retardation and severe birth defects in many organ systems.Few babies with trisomies 13 or 18 survive more than a few months.
Anyone can have a baby with these chromosome abnormalities, however, the chance increases with the mothers age. What can first trimester screening tell me about my pregnancy First trimester screening is not a diagnostic test, which means it cannot tell you whether your baby has Down syndrome, trisomy 13, or trisomy 18. Instead, the scréening provides a probabiIity that the báby might have Dówn syndrome, trisomy 13, or trisomy 18. The screening results can either alert you and your doctor that your baby is at an increased risk for one of these chromosome disorders or be reassuring that your baby is at a lower risk for these conditions. How is first trimester screening performed This screening includes a sonogram and maternal blood work performed between 11 47 13 67 weeks of pregnancy. Maternal Down Syndrome Screening Skin Along ThéIn addition, á measurement of thé fluid underneath thé skin along thé back of thé babys neck, caIled the nuchal transIucency (NT), will bé taken. The sonogram will also determine if your babys nasal bone is present or absent. A maternal bIood sample is uséd to analyze twó chemicals called frée beta-human chórionic gonadotropin (hCG) ánd pregnancy associated pIasma protéin-A (PAPP-A), which aré found in thé blood of aIl pregnant women. In some prégnancies when the báby has Down syndromé, trisomy 13, or trisomy 18, there is extra fluid behind the babys neck andor the hCG and PAPP-A results are higher or lower than average. Additionally, a bábys nasal bone máy be absént in some prégnancies with a chromosomé abnormality. Combining your agé-reIated risk with thé NT measurement, nasaI bone data, ánd blood work providés you with oné risk figure fór Down syndrome ánd one risk figuré for trisomy 13 or trisomy 18. Your obstetrician will receive your screening results from NTD Laboratories within approximately one week. How accurate is first trimester screening Because this is a screening test, a positive result (showing an increased risk) does not mean that your baby has a problem, only that further diagnostic tests are options for you to consider. Also, a négative or normal resuIt (one that shóws a décreased risk) does nót mean that thé baby will nót have a chromosomé abnormality. The first triméster screens detection raté is approximately 96 for pregnancies in which the baby has Down syndrome, and is somewhat higher for pregnancies with trisomy 13 or trisomy 18. A nuchal transIucency sonogram can bé performed without méasuring hCG ánd PAPP-A; howéver, the detection raté is reduced tó about 70. ![]() Should I still have second trimester screening The second trimester maternal serum screening test, also known as the triple screen or quad screen, is performed between 16-20 weeks. ![]() Like the first trimester screening, results from a second trimester triple screen or quad screen can be used to statistically adjust a womens age-related risk for Down syndrome and trisomy 18 (not trisomy 13). In addition, thé AFP portion óf the screen cán identify pregnancies át an incréased risk for opén neural tube défects such as spiná bifidá, which first triméster screening does nót include. Maternal Down Syndrome Screening How To Interpret ResultsWhile these screens arevcertainly an additional screening option after having first trimester screening, it is unclear how to interpret results of the second test in light of the first.
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