**2. Central nervous system**

is responsible for this thickening and that it was possible to measure the thickness of this fluid at the back of the neck around the third month of pregnancy [2, 3]. A thicker nuchal translucency might suggest chromosomal abnormality, but it can be present in cardiovascular

NT is usually measured around 11–13 weeks of gestation. The thickness of the nuchal oedema is proportional to the crown-rump length (CRL) of the fetus so it is measured when the CRL is 45–84 mm. The higher the NT is at a specific CRL, the higher the risk for chromosomal abnormalities is [2]. For example, in Turner-syndrome, the NT value is around 8 mm higher than

In Down-syndrome, nasal bone is absent in 60–70% of the affected fetuses. Langdon Down observed that those with 21-trisomy had small noses, caused by the hypoplasia of the nasal bone. The hypoplasia of the nasal bone can also be detected during pregnancy. According to a meta-analysis, the nasal bone was absent in 1.4% of healthy fetuses, while in 69% of fetuses with trisomy 21. Furthermore, the maxilla was shorter in 25% of the affected fetuses, and duc-

In Edwards-syndrome (trisomy 18), early growth retardation and bradycardia can be detected at 11–13 weeks. Also, the nasal bone is absent in 55% of the cases and 75% has a singular artery in

In Patau syndrome (trisomy 13), 70% of the fetuses have tachycardia. Early growth retarda-

The second ultrasound screening is usually done around 18–20 weeks of gestation. The goal of this screening is to diagnose congenital malformations and to detect other signs of chromosome anomalies and other syndromes. Therefore, this ultrasound examination is called

• abdominal wall (anteroposterior and transversal diameter-AD, abdominal circumference-AC)

tion, megacystis and holoprosencephaly are also frequently present [2].

• cranium (BPD, occipito-frontal diameter-OFD, head circumference-HC)

malformations and genetic syndromes as well.

4 Congenital Anomalies - From the Embryo to the Neonate

tus venosus flow was abnormal in 80% [1, 2].

the median [2].

the umbilical cord.

"genetic screening."

• spine (spina bifida)

• stomach (filling of the stomach)

• extremities (femur length-FL, humerus length-HL)

• face

• heart

• diaphragm

• kidneys, bladder

• amniotic fluid

• placenta, umbilical cord

• uterine artery Doppler

Structures to be examined:

Brain anomalies are one of the most common group of congenital malformations. To be examined: the cerebellum, choroid plexuses, cisterna magna, lateral ventricles, cavum septi pellucidi. There are three major scan planes for the fetal brain:


Any abnormality in these views may suggest a brain malformation, such as: neural tube defects, ventriculomegaly, holoprosencephaly, hydranencephaly, Dandy-Walker malformation, agenesis of the corpus callosum, porencephaly, intracranial tumor. The sensitivity of the ultrasound is high in the diagnosis of these malformations [5, 6].

Neural tube defects (NTDs) are the second most common types of malformations. The incidence of NTDs is around 1:1000 in the USA and 8:1000 in the UK. Anencephaly, encephalocele/meningocele and spina bifida are the most common NTDs [7–9].

Anencephaly is the absence of a major portion of the skull and the brain hemispheres caused by an abnormal closure in the cranial part of the brain. Exencephaly is an early stage of anencephaly, when the brain is still present but is located outside the skull. Anencephaly develops as the neural tissue degenerates. Exencephaly can be detected by first trimester ultrasound as floating brain tissue outside of the skull. CRL is usually lower than normal. In the second and third trimester, polyhydramnios is usually also present. Anencephaly is a fatal condition and most affected pregnancies are terminated after the diagnosis [7, 8].

Encephalocele and meningocele are defects of the skull. In the former, brain tissue and meninges protrude through the defect of the skull, while in the latter only the meninges are affected. The defect of the skull can be detected with ultrasound. In 75% of the cases the defect is occipital.

Spina bifida is present when the spine does not close properly. There are three types based on what structures are affected:

	- **a.** meningocele: contains meninges and cerebrospinal fluid
	- **b.** myelomeningocele: contains meninges, cerebrospinal fluid and neural structures

**Figure 1.** Spina bifida cystic. The spine does not close properly. The cystic protrusion contains meninges and cerebrospinal fluid.

The ultrasound detection rate of spina bifida is almost 100% thanks to the specific markers: banana and lemon signs (**Figure 2**), small posterior fossa, small cerebellum, and ventriculomegaly. Also, there is a V-shaped appearance to the posterior elements of the spine [10, 11].

a >15 mm dilation is severe. Furthermore, BPD is increased in most cases. After the detection of ventriculomegaly, toxoplasma and virus serology should be considered. When present with other anomalies, chromosomal examination is also due. The postnatal management is

**Figure 3.** Agenesis/dysgenesis of corpus callosum. The teardrop shaped lateral ventricles, in some cases absence of a

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normal cavum septi pellucidi, dilatation of the third ventricle may suggest this malformation.

Holoprosencephaly is present when the prosencephalon (forebrain) of the embryo fails to divide into two hemispheres. This causes a sequence of malformations: cyclopia, cyclotia, ethmocephalia, proboscis, cebocephalia, premaxillary agenesis, cheilognathopalatoschisis.

**1.** alobar: the longitudinal fissure, the falx cerebri, the septum pellucidum and the corpus

**3.** lobar: hemispheres are separated, absence of the septum pellucidum, fusion of the lateral

Birth prevalence is around 1:10,000–1:15,000, but the prevalence is much higher in miscarriages. Chromosome abnormality is associated in half of the cases, most frequently 13-trisomy. The alobar type is fatal, while patients with lobar or semilobar holoprosencephaly suffer from severe

Agenesis of the corpus callosum (ACC) (**Figure 3**) is among the most frequent malformations of the developing brain with an incidence of around 5:1000 [8, 11]. Corpus callosum can be visualized at the end of the first trimester using the Doppler flow technic [2]. The absence of a normal cavum septi pellucidi, teardrop shaped lateral ventricles, colpocephaly and dilatation

Dandy-Walker malformation consists of hydrocephaly, hypoplasia/agenesis of the cerebellar vermis and dilatation of the fourth ventricle (cyst of the posterior fossa). The birth prevalence is 1:12,000. Dilation of the cisterna magna and the forth ventricle can be seen on the ultrasound [5, 8].

shunt implantation in most cases [4, 5, 11].

physical and mental disabilities [4, 5, 18].

of the third ventricle may suggest ACC [4, 11].

**2.** semilobar: the frontoparietal part of the brain is undivided

**4.** arhinencephaly: absence or hypoplasia of the olfactory tract and bulb

Types of holoprosencephaly:

callosum are absent

ventricles

Around 88% of all NTDs can be detected with prenatal ultrasound (25–94%) [12]. More than 90% of anencephaly and encephalocele cases are detected, while only 44% of fetuses with spina bifida are diagnosed in the first trimester [13–15]. However, the efficacy of ultrasound in the detection of spina bifida is 92–95% in the second trimester [12, 16–18].

In ventriculomegaly, the ventricles are dilated by the cerebrospinal fluid. Fluid accumulation in the ventricles is caused by excessive production, abnormal absorption or impaired circulation. The pressure increases in the ventricles and compresses and ultimately damages the brain tissue (internal hydrocephaly). When the amount of cerebrospinal fluid increases in the subarachnoid space, we talk about external hydrocephaly. Macrocephaly is when the skull is dilated too. The first sign on the ultrasound is usually the dilation of the occipital horn of the lateral ventricles. We talk about ventriculomegaly, when the dilation is larger than 8 mm at 18 weeks of gestation. Later in pregnancy, ventriculomegaly is present when the lateral ventricle/hemisphere ratio is higher than 0.5 (**Figure 3**) [4, 5]. When measured in the atrium (the connecting point of the occipital and temporal horns), a 10–15 mm dilation is mild, while

**Figure 2.** Lemon sign. In cases of spina bifida, special signs like lemon sign are visible in some cases.

**Figure 3.** Agenesis/dysgenesis of corpus callosum. The teardrop shaped lateral ventricles, in some cases absence of a normal cavum septi pellucidi, dilatation of the third ventricle may suggest this malformation.

a >15 mm dilation is severe. Furthermore, BPD is increased in most cases. After the detection of ventriculomegaly, toxoplasma and virus serology should be considered. When present with other anomalies, chromosomal examination is also due. The postnatal management is shunt implantation in most cases [4, 5, 11].

Holoprosencephaly is present when the prosencephalon (forebrain) of the embryo fails to divide into two hemispheres. This causes a sequence of malformations: cyclopia, cyclotia, ethmocephalia, proboscis, cebocephalia, premaxillary agenesis, cheilognathopalatoschisis.

Types of holoprosencephaly:

The ultrasound detection rate of spina bifida is almost 100% thanks to the specific markers: banana and lemon signs (**Figure 2**), small posterior fossa, small cerebellum, and ventriculomegaly. Also, there is a V-shaped appearance to the posterior elements of the spine [10, 11]. Around 88% of all NTDs can be detected with prenatal ultrasound (25–94%) [12]. More than 90% of anencephaly and encephalocele cases are detected, while only 44% of fetuses with spina bifida are diagnosed in the first trimester [13–15]. However, the efficacy of ultrasound

**Figure 1.** Spina bifida cystic. The spine does not close properly. The cystic protrusion contains meninges and cerebrospinal

In ventriculomegaly, the ventricles are dilated by the cerebrospinal fluid. Fluid accumulation in the ventricles is caused by excessive production, abnormal absorption or impaired circulation. The pressure increases in the ventricles and compresses and ultimately damages the brain tissue (internal hydrocephaly). When the amount of cerebrospinal fluid increases in the subarachnoid space, we talk about external hydrocephaly. Macrocephaly is when the skull is dilated too. The first sign on the ultrasound is usually the dilation of the occipital horn of the lateral ventricles. We talk about ventriculomegaly, when the dilation is larger than 8 mm at 18 weeks of gestation. Later in pregnancy, ventriculomegaly is present when the lateral ventricle/hemisphere ratio is higher than 0.5 (**Figure 3**) [4, 5]. When measured in the atrium (the connecting point of the occipital and temporal horns), a 10–15 mm dilation is mild, while

in the detection of spina bifida is 92–95% in the second trimester [12, 16–18].

fluid.

6 Congenital Anomalies - From the Embryo to the Neonate

**Figure 2.** Lemon sign. In cases of spina bifida, special signs like lemon sign are visible in some cases.


Birth prevalence is around 1:10,000–1:15,000, but the prevalence is much higher in miscarriages. Chromosome abnormality is associated in half of the cases, most frequently 13-trisomy. The alobar type is fatal, while patients with lobar or semilobar holoprosencephaly suffer from severe physical and mental disabilities [4, 5, 18].

Agenesis of the corpus callosum (ACC) (**Figure 3**) is among the most frequent malformations of the developing brain with an incidence of around 5:1000 [8, 11]. Corpus callosum can be visualized at the end of the first trimester using the Doppler flow technic [2]. The absence of a normal cavum septi pellucidi, teardrop shaped lateral ventricles, colpocephaly and dilatation of the third ventricle may suggest ACC [4, 11].

Dandy-Walker malformation consists of hydrocephaly, hypoplasia/agenesis of the cerebellar vermis and dilatation of the fourth ventricle (cyst of the posterior fossa). The birth prevalence is 1:12,000. Dilation of the cisterna magna and the forth ventricle can be seen on the ultrasound [5, 8].

Based on our findings, 255 out of 351 congenital craniospinal malformations were diagnosed prenatally (72.65%).

[18, 22, 23]. 30–40% of these anomalies occur in association with other malformations or chro-

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Risk factors are abnormal NT, heart malformation in the mother's history (mother, family, previous pregnancies), diabetes of the mother, heart rate anomalies in early pregnancy, teratogenic explosion in early pregnancy. The presence of even one of these factors means that the pregnancy

Low-risk pregnant women go through a routine screening ultrasound at 18–22 weeks. During routine screening both the four-chamber and the two outflow tract views are to be examined. The four-chamber view can be visualized in a transversal plane above the diaphragm. The size of the fetal heart, its location, rhythm, the cardiac axis, the two atriums, the two ventricles, the ventricular septum, the atrial septum primum and the atrioventricular valves can be examined in this view [27]. Around 60% of major cardiovascular malformations can be detected in the four-chamber plane. The outflow tract views (left and right) give information about the anatomy of the aorta, pulmonary artery, aortic and pulmonary valves and the origin of the aorta and pulmonary arteries. They can be visualized by sliding the transducer toward the fetal head from a four-chamber view [27]. The detection rate of cardiovascular anomalies was higher when the four-chamber and outflow tract views were

In the high-risk group, an early fetal echocardiography is performed. Fetal echocardiography can be done from 11 weeks of gestation, and almost all of the malformations can be detected by 14 weeks (84–95%) [28, 29]. The examination can be repeated around 20 weeks. Cardiomyopathies, valvular stenosis, and tumors can only be detected later in pregnancy [5, 30].

In our study, 67.7% of all cardiovascular malformations were diagnosed with ultrasound. We found high ultrasound sensitivity in the univentricular heart (96.43%), pericardial effusion (90.91%) and hypoplastic left heart syndrome (90%) groups. Though, atrial septum defect and pulmonary artery malposition cases were detected with the lowest sensitivity (31.71%

Malformations of the lung are rare anomalies, but diagnosing them prenatally is still important, especially to determine appropriate postnatal management. At 18 weeks of pregnancy, the lungs can be visualized around the heart, filling two-third of the thorax. The quantity of the amniotic fluid has an important role in the development of the lungs. Therefore, in severe oligohydram-

Cystic malformations of the lungs can be separated into three groups: solitary and multiplex cystic anomalies and congenital cystic adenomatoid malformation (CCAM). The latter is a multicystic hamartoma that is usually confined to only one lobe. 47–80% of all lung malformations are CCAMs with a prevalence of 0.3–0.9/10,000 [31–33]. Ultrasound detection depends on the size of the cyst: Type I: 10–20 mm, Type II: 5–10 mm, Type III: small, not detectable.

mosomal abnormalities [24, 25].

all examined [5, 26, 27].

and 33.33%).

**5. Lungs, diaphragm**

nios the lungs become hypoplastic (Potter-sequence).

is high risk for congenital heart malformations [5, 23, 26].

We found that the sensitivity of ultrasound was high in case of the anencephaly/exencephaly (95%), spina bifida (88.89%), hydanencephaly (87.5%) and ventriculomegaly (80%) groups. However, the sensitivity of ultrasound was lower in the corpus callosum agenesis (50%), microcephaly (25%) and Arnold-Chiari malformation groups.
