The correlation with abnormal fetal outcome and a high level of amniotic fluid alpha-fetoprotein in mid-trimester.

OBJECTIVE: To evaluate the correlation of high levels [>2.0 multiples of median (MoM)] of amniotic fluid alpha-fetoprotein (AFAFP) in midtrimester with abnormal fetal outcome. MATERIALS AND METHODS: We retrospectively studied 6245 pregnant women with singleton pregnancy who had undergone amniocentesis between 15 and 27 weeks' gestation at Mackay Memorial Hospital between January 2014 and June 2020. Fifty-five cases had high AFAFP levels (>2.0 MoM). We investigated the abnormal fetal outcomes. RESULTS: Among the fifty-five cases with high AFAFP levels (>2.0 MoM), thirty (54.5%) had fetal chromosomal abnormalities, major structural abnormalities, and/or adverse obstetric events. Eight cases (14.5%) had chromosomal abnormalities including trisomy 21 (3 cases), trisomy 18 (3 cases), mosaic trisomy 18 (1 cases), and mosaic ring 13 (1 case). Seventeen cases (30.9%) had major structural abnormalities including abdominal wall defect (6 cases) and central nervous system (5 cases), gastrointestinal tract (3 cases), cardiovascular (2 cases), and genitourinary tract (2 cases) abnormalities. Fifteen cases (27%) had adverse obstetric events, including preterm delivery (5 cases), intrauterine fetal demise (4 cases), small for gestational age (4 cases), preeclampsia (4 cases), gestational diabetes mellitus (2 cases), gestational hypertension (1 case), preterm prelabor rupture of membrane (1 case), prolonged labor (1 case), and preterm uterine contraction (1 case). CONCLUSION: A high AFAFP level (>2.0 MoM) in midtrimester can be associated with abnormal fetal outcome, including chromosomal abnormalities, major structural abnormalities, and adverse obstetric events. Women with a prenatal diagnosis of high AFAFP levels (>2.0 MoM) should be alerted of the possibility of abnormal fetal outcomes, and further detailed genetic studies and serial sonographic examinations are recommended.

Prenatal diagnosis of persistent left superior vena cava, polyhydramnios and a small gastric bubble in a fetus with VACTERL association.

OBJECTIVE: We reported a fetus that presenting with persistent left superior vena cava (PLSVC), polyhydramnios, and a small gastric bubble during prenatal examination and identified VACTERL association after birth. CASE REPORT: A 34-year-old woman underwent amniocentesis at 18 weeks of gestation because of advanced maternal age and the result was normal. Subsequently, an ultrasound revealed single umbilical artery (SUA) at 21 weeks of gestation. She received a detailed fetal anatomy survey that presented the same findings and PLSVC. A small visible gastric bubble was noted at that time, and the other organs were unremarkable. Polyhydramnios was identified at 30 weeks of gestation and amnioreduction was subsequently performed at 32 weeks of gestation. However, polyhydramnios was persisted despite amnioreduction and intrauterine growth restriction was also detected. A cesarean section was performed because of fetal distress at 36 + 2 weeks, and a 1832-g female baby was delivered. Pre-axial polydactyly at left thumb, SUA and esophageal atresia with distal tracheoesophageal fistula (TEF) were identified after birth. The neonate died at age of 4 days because of surgical complication following esophageal anastomosis. CONCLUSION: Prenatal diagnosis of PLSVC associated with polyhydramnios and a small gastric bubble may indicate esophageal atresia with TEF, and further examination for associated syndromes such as VACTERL association is warranted.

Monozygotic twins discordant for low-level mosaic trisomy 17 at amniocentesis in a pregnancy with a favorable outcome and a literature review of heterokaryotypic monozygotic twins at amniocentesis.

OBJECTIVE: We present a set of twins discordant for low-level mosaic trisomy 17 at amniocentesis, and we review the literature of heterokaryotypic monozygotic twins at amniocentesis. MATERIALS AND METHODS: We describe a monozygotic twin pregnancy with discordant karyotypes and structural abnormalities. A 22-year-old, primigravid woman underwent amniocentesis at 21 weeks of gestation because of an abnormal maternal serum screening result for Down syndrome. Prenatal ultrasound revealed twin-twin transfusion syndrome but no detectable fetal structural abnormalities. Conventional cytogenetic analysis was applied on cultured amniocytes and parental bloods. Polymorphic DNA marker analysis by quantitative fluorescent polymerase chain reaction (QF-PCR) testing was performed on the DNAs extracted from cultured amniocytes, parental bloods and peripheral bloods of the twins after birth. Interphase fluorescence in situ hybridization (FISH) analysis was performed on buccal mucosal epithelial cells. RESULTS: Amniocentesis revealed a karyotype of 47,XX,+17 [3]/46,XX [23] in twin A and a karyotype of 46,XX in twin B. The parental karyotypes were normal. QF-PCR confirmed monozygotic twinning and excluded uniparental disomy (UPD) 17. At 35 weeks of gestation, a 1778-g twin A and a 2396-g twin B were delivered smoothly. Both infants had the karyotype of 46,XX in the peripheral bloods and were phenotypically normal except that twin A had preaxial polydactyly on the right hand. Postnatal QF-PCR testing confirmed monozygotic twinning. The infants were doing well at age 2 years and 7 months at follow-ups with normal physical and psychomotor development. FISH analysis on buccal mucosal epithelial cells showed trisomy 17 signals in 4.16% (4/96) cells, compared with 5% (5/101 cells) in normal control. CONCLUSIONS: Monozygotic twins discordant for low-level mosaic trisomy 17 at amniocentesis without ultrasound abnormalities can have a favorable outcome. Prenatal diagnosis of twins discordant for structural abnormalities and/or chromosomal aberrations should alert the possibility of monozygotic twinning, and QF-PCR testing is useful for rapid determination of zygosity and exclusion of UPD under such a circumstance.

Prenatal diagnosis of a familial 15q11.2 (BP1-BP2) microdeletion encompassing TUBGCP5, CYFIP1, NIPA2 and NIPA1 in a fetus with ventriculomegaly, microcephaly and intrauterine growth restriction on prenatal ultrasound.

OBJECTIVE: We present prenatal diagnosis of a 15q11.2 (BP1-BP2) microdeletion encompassing TUBGCP5, CYFIP1, NIPA2 and NIPA1 in a fetus with ventriculomegaly, microcephaly and intrauterine growth restriction (IUGR) on prenatal ultrasound. CASE REPORT: A 30-year-old, gravida 3, para 2, woman was referred to the hospital for amniocentesis because of fetal ventriculomegaly on prenatal ultrasound. Her husband was 31 years old. The couple had two healthy daughters, and there was no family history of mental disorders and congenital malformations. Amniocentesis revealed a karyotype of 46,XX. Array comparative genomic hybridization (aCGH) analysis on the DNA extracted from uncultured amniocytes revealed a 451.89-kb 15q11.2 microdeletion or arr 15q11.2 (22,765,628-23,217,514) × 1.0 [GRCh37 (hg19)] encompassing TUBGCP5, CYFIP1, NIPA2 and NIPA1. The parental karyotypes were normal. aCGH analysis on the DNAs extracted from parental bloods revealed a 402-kb 15q11.2 microdeletion or arr 15q11.2 (22,815,577-23,217,514) × 1.0 (hg19) encompassing TUBGCP5, CYFIP1, NIPA2 and NIPA1 in the phenotypically normal father. The mother did not have any genomic imbalance. Level II ultrasound at 21 weeks of gestation revealed microcephaly and IUGR. The parents elected to terminate the pregnancy at 22 weeks of gestation, and a female fetus was delivered with a body weight of 448 g (10th centile) and a body length of 26 cm (3rd-10th centile) but no gross abnormalities. CONCLUSION: Fetuses with a 15q11.2 (BP1-BP2) microdeletion may present ventriculomegaly, microcephaly and IUGR on prenatal ultrasound, and aCGH is helpful for prenatal diagnosis under such a circumstance.

Prenatal diagnosis of a familial 5p14.3-p14.1 deletion encompassing CDH18, CDH12, PMCHL1, PRDM9 and CDH10 in a fetus with congenital heart disease on prenatal ultrasound.

OBJECTIVE: We present prenatal diagnosis of a familial 5p14.3-p14.1 deletion in a fetus with congenital heart disease on prenatal ultrasound. CASE REPORT: A 33-year-old woman underwent amniocentesis at 18 weeks of gestation because of fetal ventricular septal defect (VSD) and echogenic bowel on prenatal ultrasound. Amniocentesis revealed a karyotype of 46,XX,del (5) (p14p14). Simultaneous array comparative genomic hybridization (aCGH) analysis on the DNA extracted from uncultured amniocytes revealed a 5.589-Mb 5p14.3-p14.1 deletion or arr 5p14.3p14.1 (19, 497, 649-25,086,268) × 1.0 [GRCh37 (hg19)] encompassing CDH18, CDH12, PMCHL1, PRDM9 and CDH10. Cytogenetic and aCGH analyses of the parents showed that the phenotypically normal mother carried the 5p14.3-p14.1 deletion. The father did not have such a deletion. The parents elected to continue the pregnancy, and a 3426-g female baby was delivered at 38 weeks of gestation with no gross abnormalities. The infant postnatally manifested VSD, atrial septal defect and patent ductus areriosus, and underwent cardiac surgery to treat the congenital heart disease. When follow-up at age 1 year and 4 months, she had a body weight of 8.8 Kg (50th-75th centile), a body height of 75.6 cm (85th-95th centile) and normal psychomotor development. CONCLUSION: Fetuses with a 5p14.3-p14.1 deletion may present congenital heart disease on prenatal ultrasound, and aCGH is helpful for prenatal diagnosis under such a circumstance.

Prenatal diagnosis of a familial 1q21.1-q21.2 microdeletion in a fetus with polydactyly of left foot on prenatal ultrasound.

OBJECTIVE: We present prenatal diagnosis of a familial 1q21.1-q21.2 microdeletion in a fetus with polydactyly of left foot on prenatal ultrasound. CASE REPORT: A 30-year-old, gravida 2, para 1, woman underwent amniocentesis at 22 weeks of gestation because of fetal polydactyly of left foot and echogenic heart foci on prenatal ultrasound. She and her husband and the 2-year-old son were healthy, and there was no family history of mental disorders, skeletal abnormalities and congenital malformations. Amniocentesis revealed a karyotype of 46,XX. Simultaneous array comparative genomic hybridization (aCGH) analysis on the DNA extracted from uncultured amniocytes revealed a 1.317-Mb 1q21.1-q21.2 microdeletion encompassing PRKAB2, FMO5, CHD1L, BCL9, ACP6, GJA5, GJA8 and GPR89B. aCGH analysis of the family members revealed that the phenotypically normal father and elder son carried the same 1q21.1-q21.2 microdeletion. The mother did not have such a deletion. The parents elected to continue the pregnancy, and a 3416-g female baby was delivered at 40 weeks of gestation with neither facial dysmorphism nor gross abnormalities except postaxial polydactyly of the left foot. CONCLUSION: Fetuses with a 1q21.1-q21.2 microdeletion may present polydactyly on prenatal ultrasound, and aCGH is helpful for prenatal diagnosis under such a circumstance.

Prenatal diagnosis of a 3.2-Mb 2p16.1-p15 duplication associated with familial intellectual disability.

OBJECTIVE: We present prenatal diagnosis of a 2p16.1-p15 duplication associated with familial intellectual disability, and we discuss the genotype-phenotype correlation. CASE REPORT: A 22-year-old, primigravid woman underwent amniocentesis at 22 weeks of gestation because of a family history of intellectual disability. The woman and her two sisters had intellectual disability but no behavioral disorders. The intellectual disability was noted in at least one paternal aunt and six paternal cousins of the woman. Cytogenetic analysis revealed the karyotype of 46,XX in the fetus and the two women. Array comparative genomic hybridization (aCGH) analysis on the DNAs extracted from cultured amniocytes and the bloods of the woman and the her sister revealed a 3.244-Mb duplication of 2p16.1-p15 or arr 2p16.1p15 (58,288,588-61,532,538) × 3.0 [GRCh37 (hg19)] encompassing eight Online Mendelian Inheritance in Man (OMIM) genes of VRK2, FANCL, BCL11A, PAPOLG, REL, PUS10, PEX13 and USP34 in the fetus and the two women. Prenatal ultrasound findings were unremarkable. The woman elected to continue the pregnancy. A 3244-g female baby was delivered at term with neither craniofacial dysmorphism nor structural abnormalities. CONCLUSION: aCGH is useful in prenatal diagnosis of inherited subtle chromosome imbalance in pregnancy with familial intellectual disability. Chromosome 2p16.1-p15 duplication can be associated with intellectual disability.

A 13-year-old girl with 18p deletion syndrome presenting Turner syndrome-like clinical features of short stature, short webbed neck, low posterior hair line, puffy eyelids and increased carrying angle of the elbows.

OBJECTIVE: We report a 13-year-old girl with 18p deletion syndrome presenting Turner syndrome-like clinical features. CASE REPORT: A 13-year-old girl was referred for genetic counseling of Turner syndrome-like clinical features of short stature, short webbed neck, low posterior hair line, puffy eyelids and increased carrying angle of the elbows. The girl also had mild intellectual disability, psychomotor developmental delay, speech disorder, high-arched palate, hypertelorism and mid-face hypoplasia. Cytogenetic analysis of the girl revealed a karyotype of 46,XX,del(18) (p11.2). The parental karyotypes were normal. Array comparative genomic hybridization analysis on the DNA extracted from the peripheral blood revealed a 13.93-Mb deletion of 18p11.32-p11.21 or arr 18p11.32p11.21 (148,993-14,081,858) × 1.0 [GRCh37 (hg19)] encompassing 52 Online Mendelian Inheritance in Man (OMIM) genes including USP14, TYMS, SMCHD1, TGIF1, LAMA1, TWSG1, GNAL and PTPN2. Polymorphic DNA marker analysis revealed a maternal origin of the deletion. CONCLUSION: Females with Turner syndrome-like clinical features in association with intellectual disability, facial dysmorphism and psychomotor developmental delay should be suspected of having chromosome deletion syndromes.

Prenatal diagnosis of short-rib polydactyly syndrome type III or short-rib thoracic dysplasia 3 with or without polydactyly (SRTD3) associated with compound heterozygous mutations in DYNC2H1 in a fetus.

OBJECTIVE: We present the perinatal imaging findings and molecular genetic analysis in a fetus with short-rib polydactyly syndrome (SRPS) type III or short-rib thoracic dysplasia 3 with or without polydactyly (SRTD3). CASE REPORT: A 29-year-old, primigravid woman was referred for genetic counseling at 15 weeks of gestation because of abnormal ultrasound findings of short limbs, a narrow chest and bilateral polydactyly of the hands and feet, consistent with a diagnosis of SRPS type III. Chorionic villus sampling was performed, and targeted next-generation sequencing (NGS) was applied to analyze a panel of 25 genes including CEP120, DYNC2H1, DYNC2LI1, EVC, EVC2, FGFR2, FGFR3, HOXD10, IFT122, IFT140, IFT172, IFT52, IFT80, KIAA0586, NEK1, PAPSS2, SLC26A2, SOX9, TCTEX1D2, TCTN3, TTC21B, WDR19, WDR34, WDR35 and WDR60. The NGS analysis identified novel mutations in the DYNC2H1 gene. The fetus was compound heterozygous for a missense mutation c.8077G > T (p.Asp2693Tyr) of paternal origin in DYNC2H1 and a frameshift mutation c.11741_11742delTT (p.Phe3914X) of maternal origin in DYNC2H1. The fetus had a karyotype of 46,XY, and postnatally manifested characteristic SRPS type III phenotype. CONCLUSION: Targeted NGS is useful in genetic diagnosis of fetal skeletal dysplasia and SRPS, and the information acquired is helpful in genetic counseling.

Prenatal diagnosis of hydrancephaly and enlarged cerebellum and cisterna magna in a fetus with thanatophoric dysplasia type II and a review of prenatal diagnosis of brain anomalies associated with thanatophoric dysplasia.

OBJECTIVE: We present prenatal diagnosis of hydrancephaly and enlarged cerebellum and cisterna magna in a fetus with thanatophoric dysplasia type II (TD2) and a review of prenatal diagnosis of brain anomalies associated with TD. CASE REPORT: A 33-year-old woman was referred for genetic counseling at 25 weeks of gestation because of fetal ultrasound abnormalities. Prenatal ultrasound at 14 weeks of gestation revealed an increased nuchal translucency (NT) and hydrocephalus. Level II ultrasound examination at 25 weeks of gestation revealed hydrancephaly, macrocephaly, a cloverleaf skull, frontal bossing, enlarged cerebellum and cisterna magna, a narrow chest, small ribs, short straight limbs. Amniocentesis revealed a karyotype of 46,XX. FGFR3 mutation analysis using the DNA extracted from uncultured amniocytes revealed a genotype of WT/c.1948A>G (p.Lys650Glu). The result was consistent with a K650E mutation in FGFR3 and TD2. The pregnancy was subsequently terminated. CONCLUSION: Fetuses with TD2 may present increased NT, early onset hydrocephalus, enlarged cerebellum and cisterna magna, and hydrancephaly on prenatal ultrasound.

Prenatal diagnosis of a 0.7-Mb 17p13.3 microdeletion encompassing YWHAE and CRK but not PAFAH1B1 in a fetus without ultrasound abnormalities.

OBJECTIVE: We present prenatal diagnosis and molecular cytogenetic characterization of 17p13.3 microdeletion encompassing YWHAE and CRK but not PAFAH1B1 in a fetus without ultrasound abnormalities. CASE REPORT: A 33-year-old woman underwent amniocentesis at 17 weeks of gestation because of a family history of spinocerebellar atrophy in the husband. Amniocentesis revealed a karyotype of 46,XX. Simultaneously array comparative genomic hybridization (aCGH) analysis (using 60,000 probes) revealed a 0.7-Mb 17p13.3 microdeletion or arr 17p13.3 (1,264,243-1,965,733) × 1 dn [GRCh37 (hg19)] encompassing YWHAE and CRK but not PAFAH1B1. Prenatal ultrasound findings were unremarkable. There were no structural abnormalities of the brain, heart, kidneys, skull, limbs and other internal organs. The parents elected to terminate the pregnancy, and a 268-g fetus was delivered at 19 weeks of gestation with mild facial dysmorphism. Postnatal high-resolution aCGH analysis of the placenta (using 630,000 probes) showed a 0.79-Mb 17p13.3 microdeletion or arr 17p13.3 (1,173,549-1,970,690) × 1 (hg19) encompassing TUSC5, YWHAE, CRK and HIC1 but not PAFAH1B1. Metaphase fluorescence in situ hybridization analysis using the 17p13.3-specific probe of RP11-818O24 revealed a 17p13.3 deletion. CONCLUSION: Fetus with 17p13.3 microdeletion without involving PAFAH1B1 may present no brain abnormalities on fetal ultra sound.

Late-onset fetal bilateral pleural effusions associated with Down syndrome.

OBJECTIVE: We present two cases of late-onset bilateral fetal pleural effusions associated with fetal Down syndrome. CASE REPORTS: Case 1. A 33-year-old Vietnamese woman had undergone regular sonographic examinations since 23 weeks of gestation and no abnormality had been noted. However, bilateral moderate pleural effusions were found at 33 weeks of gestation, and massive pleural effusion, ascites and polyhydramnios developed at 34 weeks of gestation. Aspiration of the pleural effusion was subsequently performed. Clinical laboratory surveys of the aspiration fluid excluded toxoplasmosis and cytomegalovirus infection. Cytogenetic analysis of cultured lymphocytes derived from pleural effusion revealed a karyotype of 47,XX,+21. The parents elected to continue the pregnancy. Intrauterine fetal demise occurred at 37 weeks of gestation, and a macerated female baby was delivered. Postnatal cytogenetic analysis of the umbilical cord confirmed the prenatal diagnosis. Case 2. A 41-year-old Pakistani woman had undergone regular sonographic examinations and no abnormality had been noted. However, isolated bilateral mild pleural effusions were noted at 27 weeks of gestation. Amniocentesis revealed a karyotype of 47,XY,+21 and simultaneous array comparative genomic hybridization analysis of uncultured amniocytes confirmed the diagnosis of Down syndrome. The pregnancy was subsequently terminated. CONCLUSION: Fetuses with Down syndrome may present late-onset bilateral pleural effusions. Prenatal diagnosis of late-onset bilateral pleural effusions should raise the possibility of fetal Down syndrome and cytogenetic investigation is warranted.

Prenatal diagnosis of a 1.6-Mb 4p16.3 interstitial microdeletion encompassing FGFRL1 and TACC3 associated with bilateral cleft lip and palate of Wolf-Hirschhorn syndrome facial dysmorphism and short long bones.

OBJECTIVE: We present prenatal diagnosis of a 4p16.3 interstitial microdeletion associated with bilateral cleft lip and palate and short long bones on prenatal ultrasound, and we discuss the genotype-phenotype correlation. MATERIALS AND METHODS: A 32-year-old woman underwent amniocentesis at 22 weeks of gestation because of bilateral cleft lip and palate and short limbs on prenatal ultrasound. Conventional cytogenetic analysis was performed on cultured amniocytes and parental bloods. Oligonucleotide array comparative genomic hybridization (aCGH) was performed on the DNAs extracted from uncultured amniocytes, parental bloods and umbilical cord. Metaphase fluorescence in situ hybridization (FISH) was performed on cultured amniocytes. RESULTS: Amniocentesis revealed a karyotype of 46,XY. The parental karyotypes were normal. aCGH analysis on uncultured amniocytes revealed a 1.66-Mb interstitial microdeletion at 4p16.3 encompassing 23 Online Mendelian Inheritance of in Man (OMIM) genes including FGFRL1 and TACC3. The parents did not have such a deletion. The pregnancy was subsequently terminated, and a malformed fetus was delivered with typical Wolf-Hirschhorn syndrome (WHS) facial appearance and bilateral cleft lip and palate. aCGH analysis of the umbilical cord confirmed the prenatal diagnosis with a result of arr 4p16.3 (72,447-1,742,649) × 1.0 [GRCh37 (hg19)]. Metaphase FISH analysis of cultured amniocytes confirmed a 4p16.3 microdeletion. CONCLUSION: Haploinsufficiency of FGFRL1 and TACC3 at 4p16.3 can be associated with bilateral cleft lip and palate of WHS facial dysmorphism and short long bones. Prenatal diagnosis of facial cleft with short long bones should raise a suspicion of chromosome microdeletion syndromes.

Prenatal diagnosis and molecular cytogenetic characterization of low-level mosaicism for tetrasomy 18p at amniocentesis in a pregnancy with a favorable outcome.

OBJECTIVE: We present prenatal diagnosis of low-level mosaicism for tetrasomy 18p at amniocentesis in a pregnancy with a favorable outcome. CASE REPORT: A 40-year-old woman underwent amniocentesis at 17 weeks of gestation because of advanced maternal age. Amniocentesis revealed a de novo supernumerary isochromosome 18p in eight of 39 colonies of cultured amniocytes. The karyotype was 47,XX,+i(18)(p10)[8]/46,XX[31]. Array comparative genomic hybridization (aCGH) analysis using uncultured amniocytes revealed arr 18p11.32p11.21 [hg 19] (148,963-14,081,887) × 2-3. Repeat amniocentesis was performed at 20 weeks of gestation. Interphase fluorescence in situ hybridization (FISH) analysis showed four 18p11.22-specific probe (RP11-918F20) signals in 11.7% (12/103 cells) of uncultured amniocytes. aCGH analysis on uncultured amniocytes did not detect genomic imbalance in chromosome 18. The parental karyotypes were normal. Polymorphic DNA marker analysis excluded uniparental disomy 18. Cytogenetic analysis of cultured amniocytes at repeat amniocentesis revealed a karyotype of 47,XX,+i(18)(p10)[2]/46,XX[12]. Prenatal ultrasound was unremarkable. The pregnancy was carried to 38 weeks of gestation, and a 2742-g phenotypically normal female baby was delivered with a cord blood karyotype of 46,XX. When examined at 8 months of age, the infant was normal in growth and psychomotor development. Interphase FISH analysis on 21 uncultured urinary cells revealed normal signals in all cells and no mosaic tetrasomy 18p. CONCLUSION: Low-level mosaic tetrasomy 18p at amniocentesis without ultrasound abnormalities can be associated with a favorable outcome.

Prenatal diagnosis of low-level mosaicism for trisomy 13 at amniocentesis associated with a favorable outcome.

OBJECTIVE: We present prenatal diagnosis of low-level mosaicism for trisomy 13 at amniocentesis associated with a favorable outcome. CASE REPORT: A 35-year-old woman underwent amniocentesis at 18 weeks of gestation because of advanced maternal age. Amniocentesis revealed a karyotype of 47,XY,+13[5]/46,XY[20]. Oligonucleotide array comparative genomic hybridization (aCGH) analysis on uncultured amniocytes revealed arr [GRCh37] (13)×3 [0.10], (X,Y)×1 compatible with trisomy 13 mosaicism. Prenatal ultrasound was unremarkable. Repeat amniocentesis was performed at 21 weeks of gestation. Interphase fluorescence in situ hybridization (FISH) analysis on uncultured amniocytes revealed a mosaic trisomy 13 level of 10% (10/100 cells). aCGH analysis on uncultured amniocytes revealed a result of arr 13q12.11q34 (20,407,323-115,092,619)×2.1 with a log2 ratio of 0.06 compatible with a 10% level of mosaicism. Polymorphic DNA marker analysis excluded uniparental disomy 13. The parental karyotypes were normal. Conventional cytogenetic analysis using cultured amniocytes at repeat amniocentesis revealed a karyotype of 46,XY in 23/23 colonies. The pregnancy was carried to 37 weeks of gestation, and a 3600-g phenotypically normal male baby was delivered. When examined at 8 months of age, the infant was doing well and was normal in psychomotor and growth development. The peripheral blood had a karyotype of 46,XY, and interphase FISH analysis on uncultured urinary cells revealed a mosaic trisomy 13 level of 4.4% (2/45 cells). CONCLUSION: Low-level true mosaicism for trisomy 13 at amniocentesis without ultrasound abnormalities can be associated with a favorable fetal outcome.