33% of pregnancies are trisomic.# The risk of Down syndrome as per maternal age:0 (OP Ghai 7th!613)- 1:1550 if age 15-29 yrs- 1:800 at 30-34 yrs- 1:270 at 35-39 yrs- 1: 100 at 40-44 yrs- 1: 50 after 45 yrs.Autosomal trisomies:TrisomyFeaturesClues to rememberDown syndrome(trisomy 21), 1:700Findings: intellctual disability, flat facies, prominent epicanthal folds, single palmar crease, gap between 1st 2 toes, duodenal atresia, Hirschsprung disease, congential heart disease (most commonly ostium primum-type atrial septal defect ), Brushfield spots. Associated with - risk of ALL, AML, and Alzheimer disease (>35 years old).95% of cases due to meiotic nondisjunction of homologous chromosomes (associated with advanced maternal age; from 1:1500 in women 45 years old).4% of case due to Robertsonian translocation1% of cases due to mosaicism (no maternal association; post-fertilization mitotic error).Drinking age (21).Most common viable chromosomal disorder and most common cause of genetic intellectual disability.First-trimester ultrasound commonly shows; | nuchal translucency and hypoplastic nasal bone; serumPAPP-A is |, free b-hCG is |.Second-trimester quad screen shows; |a-fetoprotein, |b-hCG, | estriol, | inhibin A.Edwards syndrome (trisomy 18), 1:8000Findings: severe intellectual disability, rocker-bottom feet, micrognathia (small jaw), low-set Ears, clenched hands, prominent occiput, congenital heart disease, Death usually occurs within 1 year of birth.Election age (18).Most common trisomy resulting in live birth after Down syndrome.PAPP-A and free b-hCG are | in first trimester. Quad screenshows: |a-fetoprotein, | b-hCG, | estriol, | or normal inhibin A.Patau syndrome (trisomy 13), 1:15000Findings: severe intellectual disability, rocker-bottom feet, microphthalmia, microcephaly, cleft lip/Palate, holoProsencephaly, Polydactyly, congenital heart disease. Death usually occurs within 1 year of birth.Puberty (13).First-trimester pregnancy screen showns: | free b-hCG, | PAPP-A, and | nuchal translucency.">