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Megacystis at 10-14 weeks of gestation: chromosomal defects and outcome according to bladder length
A W Liao1, N J Sebire, L Geerts
1Harris Birthright Research Centre for Fetal Medicine, King's College Hospital Medical School, London, UK.
Insights
Fetal megacystis, a bladder enlargement, has a 25% risk of chromosomal defects when measuring 7-15 mm. In normal karyotypes, 90% resolve spontaneously, but larger diameters indicate poor outcomes.
Area of Science:
- Prenatal diagnosis
- Fetal medicine
- Medical genetics
Background:
- Fetal megacystis, defined as a longitudinal bladder diameter of 7 mm or more at 10-14 weeks gestation, is a condition requiring careful evaluation.
- Understanding the association between fetal megacystis size and chromosomal abnormalities is crucial for accurate prognosis.
Purpose of the Study:
- To determine the prevalence of chromosomal defects in fetuses with megacystis.
- To analyze the pregnancy outcomes in relation to fetal bladder size and karyotype.
Main Methods:
- A cohort of 145 fetuses with megacystis (longitudinal bladder diameter ≥ 7 mm) at 10-14 weeks gestation were studied.
- Fetal karyotype and pregnancy outcomes were assessed, correlating with the longitudinal bladder diameter.
Main Results:
- Chromosomal defects, primarily trisomies 13 and 18, were found in 30 cases.
- A bladder diameter of 7-15 mm showed a 23.6% incidence of chromosomal defects, while >15 mm had an 11.4% incidence.
- Spontaneous resolution occurred in 90% of chromosomally normal fetuses with 7-15 mm bladder diameter; none resolved if >15 mm.
Conclusions:
- Fetal megacystis measuring 7-15 mm carries a ~25% risk of chromosomal defects, with spontaneous resolution in ~90% of normal karyotypes.
- Bladder diameters >15 mm indicate a ~10% risk of chromosomal defects and are invariably linked to progressive obstructive uropathy in chromosomally normal fetuses.
Aims:
To examine the prevalence of chromosomal defects and outcome of fetuses with megacystis at 10-14 weeks of gestation.
Methods:
At the 10-14-week scan fetal megacystis was defined by a longitudinal bladder diameter of 7 mm or more. In 145 such fetuses the fetal karyotype and pregnancy outcome were examined in relation to the longitudinal diameter of the fetal bladder.
Results:
Chromosomal defects, mainly trisomies 13 and 18, were present in 30 cases. In the group with longitudinal bladder diameter of 7-15 mm the incidence of chromosomal defects was 23.6% (26/110), whereas in those with bladder diameter > 15 mm the incidence was 11.4% (4/35). The fetal nuchal translucency (NT) was above the 95th centile of the normal range for crown-rump length in a higher proportion of cases with abnormal rather than normal karyotype (76.7% compared to 31.3%; Chi-square P < 0.0001). The expected number of cases of trisomy 21, estimated on the basis of maternal age, gestational age and fetal NT, was 6.2 rather than the observed 2 and the corresponding numbers for trisomies 13 or 18 were 4.2 for expected and 24 for observed. In the chromosomally normal group with longitudinal bladder diameter of 7-15 mm follow-up scans demonstrated spontaneous resolution of the megacystis in 90% of the cases and enlargement of the megacystis and/or the development of echogenic kidneys in 10%. In contrast, none of the cases with bladder diameter > 15 mm demonstrated spontaneous resolution of the megacystis.
Conclusions:
In fetal megacystis with longitudinal bladder diameter of 7-15 mm there is a risk of about 25% that the fetus will have a chromosomal defect but in the chromosomally normal group there is spontaneous resolution of the megacystis in about 90% of cases. If the bladder diameter is > 15 mm the risk of chromosomal defects is about 10% and in the chromosomally normal group the condition is invariably associated with progressive obstructive uropathy.
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