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Twin Reversed Arterial Perfusion Sequence

Introduction Twin reversed arterial perfusion (TRAP) sequence is a rare complication specific to monochorionic twin pregnancies. As a result of early vascular disruption occurring during embryogenesis, a dysmorphic acardiac twin receives circulatory support from a pump twin via aberrant placental arterioarterial anastomoses. Because the acardiac twin is entirely dependent on perfusion from the pump twin, the pump twin is at risk of hemodynamic compromise. Originally described…

Twin-Twin Transfusion Syndrome

Introduction Twin-twin transfusion syndrome (TTTS) is a serious condition that can complicate twin pregnancies with monochorionic diamniotic (MCDA) placentation. MCDA twin pregnancies should be monitored for TTTS with serial ultrasound (US) scans beginning in the second trimester. Early-stage TTTS can be managed conservatively, but because of the unpredictable risks of disease progression and intrauterine fetal demise, prenatal testing and delivery before term should be considered. Limited…

Dichorionic Diamniotic Twin Gestations

Introduction Twin pregnancies account for more than 3% of live births in the United States. Determination of chorionicity and amnionicity is essential in the clinical management of multiple gestations. Although dichorionic twin gestations are not associated with as many fetal complications as monochorionic gestations, all twin pregnancies, whether dichorionic or monochorionic, have an increased risk of adverse pregnancy outcomes compared with singletons. Ultrasound (US) plays a…

Monochorionic Diamniotic Twin Gestations

Introduction Compared with dichorionic twin gestations, monochorionic twin gestations, whether diamniotic or monoamniotic, have an increased risk of adverse pregnancy outcomes. Ultrasound (US) plays a vital role in prenatal determination of chorionicity and in the management of monochorionic diamniotic twin pregnancies. Disease Definition The term monochorionic refers to a multiple gestation with one placental disk (or chorion), and the term diamniotic describes the presence of two…

Monochorionic Monoamniotic Twin Gestations

Introduction In addition to the general risks associated with twin pregnancies and with specific risks of monochorionic gestations, monoamniotic twin gestations face the unique risk of cord entanglement and are at increased risk of fetal demise. Ultrasound (US) plays a vital role in prenatal determination of chorionicity and amnionicity and in the prenatal management of monochorionic monoamniotic twin pregnancies. Disease Definition The term monochorionic refers to…

Chorionicity of Multiple Gestations

Introduction In 2014, the twin birth rate in the United States rose to an all-time high of 33.9 per 1000 live births. Multiple gestations result from either the fertilization of multiple ova or the division of a single fertilized ovum into more than one fetus. The terms monozygotic and dizygotic refer to the number of ova leading to a multifetal gestation. A monozygotic pregnancy results from…

Miller-Dieker Syndrome (17p13.3 Deletion Syndrome)

Introduction Miller-Dieker syndrome (MDS) is a rare, contiguous gene deletion syndrome characterized by type I lissencephaly, facial dysmorphism, seizures, and severe mental retardation. Other associated defects including cardiac malformations, neural tube defects, omphalocele, gastrointestinal anomalies, genitourinary anomalies, and intrauterine growth restriction have also been described in relationship to this syndrome. MDS is caused by a deletion at the chromosome 17p13.3 locus and is thought to represent…

Chromosome 5p Deletion Syndrome (Cri du Chat Syndrome)

Introduction Monosomy for the distal portion of the short arm of chromosome 5 causes 5p deletion syndrome, which is also known by the currently less favored term “cri du chat” syndrome, from the French description of the monotonous high-pitched “cat-like” cry of affected infants. Initially described in 1963 by Lejeune et al., this syndrome is readily detectable by karyotype or with molecular cytogenetic methods, such as chromosomal…

Chromosome 4p Deletion Syndrome (Wolf-Hirschhorn Syndrome)

Introduction First clinically described in 1961 by Hirschhorn and subsequently in 1965 by Wolf, the 4p deletion syndrome, or Wolf-Hirschhorn Syndrome (WHS), is the first example of a classic human chromosomal deletion syndrome. This rare condition, characterized by severe prenatal findings and confirmatory genetic testing, is more limited and consists of isolated case reports and small case series. Although more than 50% of deletions are visible…

22q11.2 Deletion Syndrome

Introduction The 22q11.2 deletion syndrome is the most common human chromosomal microdeletion syndrome and one of the most common syndromes associated with prenatally detected congenital heart defects (CHDs). It has a variable phenotype, with a wide range of associated clinical findings. DiGeorge syndrome, first described in 1965, is its most severe presentation, with primary symptoms of thymus and parathyroid aplasia and severe immunologic abnormalities; CHDs were…

Mosaic Trisomies 8, 9, and 16

Introduction Trisomies can occur with any chromosome, but most often result in spontaneous abortion. For example, trisomy 16 is the most common trisomy in human pregnancies, and the majority of the time results in miscarriage. These severe trisomies are more likely to survive past the first trimester and possibly to birth if they are mosaics, in which the condition of trisomy only affects a portion of…

Turner Syndrome (Monosomy X)

Introduction Turner syndrome (monosomy X) is characterized by complete or partial loss of the second X chromosome in the female, with or without cell line mosaicism. There are three distinct phenotypes: (1) first trimester abortus (98%), (2) second trimester hydrops fetalis (often resulting in fetal demise), and least commonly (3) neonate with a cystic hygroma (thin-walled cyst containing lymphatic fluid). Turner syndrome is the only monosomy…

Trisomy 21

Introduction Trisomy 21 (Down syndrome) is the most common trisomy in live-born infants and in spontaneous abortions. British physician John Langdon Down first described the syndrome in 1866. The chromosomal abnormality was discovered in 1959 by French geneticist Jerome Lejeune, and in 1961, the name Down syndrome was proposed by the editors of The Lancet . Disorder Definition Trisomy 21, also called Down syndrome, results from…

Trisomy 18

Introduction Trisomy 18 is the second most common autosomal trisomy (after trisomy 21). Disorder Definition Trisomy 18, also called Edwards syndrome, results from the presence of an extra copy of chromosome 18. Prevalence and Epidemiology Trisomy 18 is the second most common autosomal trisomy among live-born fetuses after Down syndrome. The incidence of trisomy 18, 0.6–2.5 : 10,000, is considerably lower than that for Down syndrome. It is…

Trisomy 13

Introduction Trisomy 13, also known as Patau syndrome, is one of the three most common trisomy syndromes. It is often diagnosed prenatally by the identification of one or more congenital abnormalities seen on ultrasound (US). Trisomy 13 is associated with severe physical and mental disabilities in addition to poor long-term survival rates in live-born infants. Disorder Definition First genetically described by Patau et al. in 1960, trisomy…

Triploidy

Introduction Chromosome abnormalities are often the cause of early pregnancy loss, fetal malformations, and stillbirth. Triploidy is a lethal chromosome abnormality caused by the presence of a complete extra set of chromosomes ( Fig. 148.1 ); it can lead to spontaneous miscarriage, congenital anomalies, abnormal placental appearance, and severe intrauterine growth restriction (IUGR). A triploid karyotype is also found in most cases of partial hydatidiform mole…

Introduction to Aneuploidy

Introduction Aneuploidy is a chromosomal anomaly in which the number of one or more chromosomes is abnormal. Normal human somatic cells (i.e., nonegg or sperm cells) carry 46 chromosomes: two copies of each of the 22 autosomal chromosomes and two sex chromosomes, either XX for female or XY for male. Monosomy and trisomy conditions result from the subtraction or addition of chromosomal material, respectively. Aneuploid conditions…

VATER Association

Introduction The VATER association is a nonrandom association of congenital malformations that include v ertebral anomalies, a nal atresia, t racheo e sophageal fistula, and r enal and r adial limb anomalies. This definition has been expanded to include vascular defects as well, and some have renamed this association VACTERL, so that congenital c ardiovascular defects and l imb anomalies are represented in the name. VATER…

Smith-Lemli-Opitz Syndrome

Introduction Smith-Lemli-Opitz syndrome (SLOS) is an autosomal recessive disorder caused by abnormal cholesterol synthesis. SLOS was originally named RSH syndrome, derived from the surnames of the first three families identified with this disorder. SLOS is characterized by growth failure, cognitive delay, behavioral disturbances, dysmorphic faces, and congenital malformations. There is marked variability in presentation of this condition among affected individuals. Although SLOS was historically divided into…

Sirenomelia

Introduction Sirenomelia is a rare congenital disorder that was previously considered a severe form of caudal regression, although it is currently considered a completely different entity. Also known as the mermaid syndrome , it is characterized by a variable degree of atrophy of the lower limbs, with the resultant appearance of a mermaid tail or fin ( Fig. 144.1 ). Because of the associated anomalies (particularly…