**5. Third-trimester assessment**

Later in the second trimester and in the third trimester, despite the increase in the size of the fetus, morphological examination of the limbs is more difficult because:


In certain cases, in the late second and third trimester, the secondary anatomy changes due to functional disturbances (some forms of skeletal dysplasia, fetal tumors, segmental deformations secondary to compression in oligohydramnios, multiple pregnancies, or other pathologies) become evident. Thus, even in cases with a normal morphological examination in the second trimester, the examination of the upper and lower members should be attempted in the third trimester. The commendation is stronger if such conditions are suspected.

In the third trimester, the evaluation of the fetal well-being includes the limbs and hand movements, as part of the Manning classical biophysical profile.

### **6. Literature**

**5. Third-trimester assessment**

314 Congenital Anomalies - From the Embryo to the Neonate

number of phalanges of each finger easier.

Later in the second trimester and in the third trimester, despite the increase in the size of the

**Figure 7.** Hand imaged by 3D static ultrasound (skeletal mode). The technique makes the confirmation of the normal

**Figure 5.** 2D conventional US images of normal fetal hands in midtrimester. Similarly, numbering the fingers is possible and, in certain cases, even the phalanges. As seen, in most cases, the thumb lies in a different plane than the other four fingers. Due to hand anatomy, thumb visualization may not be simultaneous than the other fingers. Yet, confirming the

**Figure 6.** Hands and foot, imaged by 3D static ultrasound (surface rendering mode). Using this technique, the

presence of the opposable finger is considered important, due to the prehension function of the hand.

demonstration of the extremities is easier, despite the different spatial arrangement of the thumb.

fetus, morphological examination of the limbs is more difficult because:

Historically, the sensitivity of prenatal ultrasound for detection of musculoskeletal and limb anomalies has been low. In 1991, Levi published a series of 16,072 pregnant women with prenatal ultrasound and found a 45.32% sensitivity for detection of any type of anomaly, with a 23.26% sensitivity for detection of limb and skeletal anomalies [25]. In 1992, Stoll found a 15% sensitivity for isolated anomalies and 48% sensitivity for multiple anomalies for the second-trimester prenatal ultrasounds [26]. The most meaningful result of these early studies is the high specificity of scanning in terms of skeletal abnormalities [25, 26]. This is important, because conditions with high false-positive rates can mislead parents and clinicians in their decisions and recommendations.

Detection of major anomalies has improved over time as a result of improvements in technology and skills, although detection of limb anomalies remained low. The Eurofetus study, in 1999, showed an overall sensitivity for detection of any anomaly to be 61%, with identification of musculoskeletal anomalies much lower and similar to the findings of Levi et al. at 18% [27].

It seems that detection of proximal limb reduction defects is better (23–50%) than detection of hand or finger limb reduction defects (0–8%) [28]. The 2005 EUROCAT study of 4366 fetuses with different anomalies reported a prenatal detection rate for both upper and lower limb reduction defects of 34% [29]. In a more recent study, a higher prenatal detection rate was found for limb reduction defects with associated malformations (49%), if compared to isolated limb reduction defects (25%) [30]. Pajkrt et al. also found a high detection rate for fetuses with short or absent radii and/or ulnae associated with aneuploidy or genetic syndromes (70%) [31]. In another large study, Gray et al. found that 31% of upper extremity anomalies were detected prenatally; however, only 18% were correctly diagnosed [32]. The missed malformations were also located distally (hand and fingers).

The difficulties in detection of upper extremity anomalies may be related to the current guidelines. They mandate only a cursory examination of the upper and lower limbs during the standard second-trimester (ST) examination. This may contribute to the high false-negative rate [33].
