The 11-13-week scan: diagnosis and outcome of holoprosencephaly, exomphalos and megacystis

Early fetal anatomical sonography

Over the past decade, prenatal screening and diagnosis has moved from the second into the first trimester, with aneuploidy screening becoming both feasible and effective. With vast improvements in ultrasound technology, sonologists can now image the fetus in greater detail at all gestational ages. In the hands of experienced sonographers, anatomic surveys between 11 and 14 weeks can be carried out with good visualisation rates of many structures. It is important to be familiar with the normal development of the embryo and fetus, and to be aware of the major anatomical landmarks whose absence or presence may be deemed normal or abnormal depending on the gestational age. Some structural abnormalities will nearly always be detected, some will never be and some are potentially detectable depending on a number of factors.

Outcome of fetal exomphalos diagnosed at 11-14 weeks of gestation

OBJECTIVE

To determine whether sonographic findings in cases of exomphalos detected at the 11-14-week scan can be used to guide pregnancy management.

METHODS

Retrospective study of cases of exomphalos identified from the Fetal Medicine Unit database, University College London Hospitals between January 1998 and January 2010. Pregnancy and neonatal data were ascertained from maternal and neonatal records. Fetal exomphalos was categorized into three groups: exomphalos associated with other major structural malformation(s), isolated exomphalos with increased nuchal translucency (NT) and isolated exomphalos with normal NT.

RESULTS

A total of 98 cases of exomphalos were identified, of which 45 (45.9%) were associated with other major structural malformation(s), identified antenatally. Isolated exomphalos was found with increased NT in 22 cases (22.4%) and with normal NT in 31 cases (31.6%). Of 80 (81.6%) fetuses that were karyotyped, 43 (53.8%) had a chromosomal abnormality; the most common aneuploidy was trisomy 18 (n = 31; 72.1%). Where exomphalos was associated with other major structural abnormalities, or was isolated with increased NT, the incidence of aneuploidy was high, at 78.9% and 72.2%, respectively. Cases of isolated exomphalos with normal NT were all euploid. In 21 cases (21.4%), exomphalos resolved later in pregnancy and none had apparent abnormalities at birth; isolated exomphalos persisted in only three neonates (3.1%).

CONCLUSIONS

The finding of a major structural abnormality or of increased NT in association with exomphalos in the first trimester implies a high risk of aneuploidy. Parents can be reassured that fetuses with isolated exomphalos and normal NT are likely to be euploid.