**3. First-trimester assessment**

Its assessment is significantly more difficult in the third trimester, as the fetal dimensions and movements frequently alter the visualization of some segments, situated far from the trans-

In the last decades, the 11–13 weeks +6 days of US genetic scan has become an important tool for fetal anatomy assessment. It includes almost all segments of the fetal body and also the upper and lower extremities. The second-trimester anomaly scan remained the standard morphologic evaluation, an audit for the early scan, and a baseline for future US evaluations and interpretation of the fetal development. Still, between the guidelines issued by the major societies, there is a wide variation of the parameters proposed as a minimum for limb evalu-

Systematic and careful examination of the extremities is important, at any time. Congenital

Usually, these limb anomalies are isolated, but detection of any of them should be followed by a detailed examination of the rest of the fetal anatomy. In many cases with aneuploidy and

> **ISUOG [1] NHS (UK) [2]**

x x —

**ACOG, AIUM, ACR, SRU** 

**[3–5]**

The fetal skeleton starts to develop early during gestation. The appendicular and axial skeletons undergo a programmed pattern of endochondral ossification during which a cartilage template is replaced by the bone. In contrast, the calvarium and portions of the clavicle and pubis ossify via membranous ossification, whereby mesenchymal cells differentiate directly

ISUOG: International Society of Ultrasound in Obstetrics and Gynecology; NHS, UK: National Health Service in the United Kingdom; ACOG: American College of Obstetricians and Gynecologists; AIUM: American Institute of Ultrasound

Limb buds begin to develop during the fourth to fifth gestational week (GW) as clusters of mesenchymal cells covered by the ectoderm, but before the end of the seventh GW, the anatomy

anomalies may affect one or more limbs and may affect any segment.

Upper and lower limb presence x x x Femur diaphysis length (measurement) x x x

Digit count — — — Fetal movement x — —

in Medicine; ACR: American College of Radiology; SRU: Society of Radiologists in Ultrasound.

**Table 1.** Recommendation for fetal limb evaluation on prenatal ultrasound.

ducer or behind other fetal bony structures.

310 Congenital Anomalies - From the Embryo to the Neonate

genetic syndromes, limb defects are present.

Metacarpal and metatarsal bones/presence of the hands

**Limb segments included in the protocol** 

ation (**Table 1**).

**recommendations**

and feet

**2. Development**

into osteoblasts [6].

During the so-called nuchal or genetic scan, a morphologic evaluation is recommended. Nuchal translucency (NT) assessment is more sensitive at an earlier gestation, 11–12 weeks of gestational age, but the optimal moment of the first-trimester anomaly scan is reported after 12 GW [8–11]. Regardless of scan timing, the fetus needs to be assessed in all planes: longitudinal, axial, and coronal. The examination may be performed transabdominal, and if necessary transvaginal, and a combination of the two approaches might give the best results [12]. In our experience, the completion of the basic protocol regarding the assessment of the fetal skeleton rarely requires an increased gestational age or the transvaginal approach, but we should keep in mind that the imaging of the fingers and feet was reported consistently and is achieved only after 12 GW [13]. Still, there was an important and constant technological progress in ultrasound capabilities since the respective researches that enables the operators to use modern systems and high-resolution probes for an earlier and a better visualization of fetal anatomy and especially the echogenic structures.

The exam should detect both upper limbs, which are often found in front of the fetal thorax or face, in semiflected position. The lower limbs are generally flexed at the hip at this gestation. The fingers are relatively easy to assess in the first trimester as number and position, including the thumb, because they frequently lie in the same ultrasound plane. Feet can also be identified, but the number of toes may be difficult to assess because of their small size. The tendency of the ankles to have an inward position may result in an overdiagnosis of clubfoot in the first trimester. The proximal long bones—femur and humerus—can be seen and measured at the first-trimester scan, although their dimensions are not part of the routine biometry at this developmental stage.

The performance of the routine first-trimester anomaly scan was reported satisfactory in a recent study [14], where all the examinations were performed transabdominal and the vast majority of limb abnormalities detected prenatally were identified in the first trimester (82%). In the respective group, 77.8% of the total limb abnormalities were diagnosed prenatally and 63.9% on the first-trimester scan.

These encouraging results followed a previous large screening study regarding the results of routine fetal anomaly evaluation at the time of genetic scan [15], where only one third of the skeletal abnormalities were diagnosed (34.12%). In the respective group, all cases of body stalk anomaly were diagnosed, but none of those with unilateral or bilateral talipes, club or claw hand, and digital defects. The correct diagnosis was made in the majority of cases of a missing hand or foot (77.8%), or polydactyly (60%), and half of the lethal skeletal dysplasia (50%) and isolated shortening of one of the long bones (50%). The only case of ectrodactyly was missed, and arthrogryposis was not suspected during the first-trimester scan.

It was suggested that a systemic sequential approach scanning from proximal to distal until the entire limb is observed, and the strict operational training and audit and the use of high-

The Antenatal Detection of Fetal Limb Anomalies http://dx.doi.org/10.5772/intechopen.76108 313

As for the most frequent limb anomalies diagnosed early in pregnancy, not only transverse limb reduction defects [14] but also radial aplasia and club hand [16] were proposed in dif-

An abnormal nuchal translucency may accompany major skeletal abnormalities [17] and sometimes may be the only early sign in conditions with discrete if any early features [18–20]. Narrowing of the thorax with secondary mediastinal compression and abnormal cutaneous

Most of the authors agree that the fetal anatomy may readily be assessed at 20–24 WG, because:

• The fetus is also enough developed to be seen, leading to good results if scanning for

Some important studies underlined a statistically significant difference being able to perform a complete fetal morphology scan if US is performed at 18 to 19 + 6 (in 76% of cases) versus 20 to 22 + 6 weeks of gestation (in 90% of cases) [21–24]. However, with the improved technological capabilities of the ultrasound equipment, the gestational age for confidently assessment is constantly lowering. On the other hand, due to absorption of sound phenomenon, the visualization of the skeleton is easier than for other fetal systems (e.g., the cardiovascular system). Also, the skeletal system is already completely developed, unlike other structures (e.g., central nervous system components, as the corpus callosum or vermis). Therefore, the fetal skeletal evaluation may be proposed and successfully performed in the routine early

**Figure 4.** 2D conventional US images of normal feet at 17 weeks of amenorrhea (WA) and at 23 WA. The normal position

resolution ultrasound machines may improve the early diagnosis of limb defects [14].

collagen deposition were discussed as possible causes (**Figures 1**–**3**).

• The pregnant uterus is completely lifted up in the maternal abdomen.

• The fetus may present favorable positions and axis for scan.

of the toe is readily observed. In many cases, numbering the digits is possible.

**4. Second-trimester assessment**

second-trimester scan (**Figures 4**–**7**).

ferent studies.

anomalies.

**Figure 1.** Normal aspects of fetal hand in the late first trimester.

**Figure 2.** Normal aspects of fetal foot in the late first trimester.

**Figure 3.** The whole fetus, imaged by 3D static ultrasound (surface rendering mode). The harmonious development and relationship between limbs' segments are easy to asses.

It was suggested that a systemic sequential approach scanning from proximal to distal until the entire limb is observed, and the strict operational training and audit and the use of highresolution ultrasound machines may improve the early diagnosis of limb defects [14].

As for the most frequent limb anomalies diagnosed early in pregnancy, not only transverse limb reduction defects [14] but also radial aplasia and club hand [16] were proposed in different studies.

An abnormal nuchal translucency may accompany major skeletal abnormalities [17] and sometimes may be the only early sign in conditions with discrete if any early features [18–20]. Narrowing of the thorax with secondary mediastinal compression and abnormal cutaneous collagen deposition were discussed as possible causes (**Figures 1**–**3**).
