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2010-05-05-14 Trisomy 13 with megacystis in the first trimester © Cerekja

Trisomy 13 with megacystis in the first trimester

Albana Cerekja
, MD, PhD*, Carlo Figliolini, MD, PhD**, Juan Piazze MD, PhD***.

*   Ultrasound Division, ASL Roma B, Rome, Italy.
**  Reparto di ostetricia e ginecologia, Ospedale Fatebenefratelli San Pietro Rome, Italy.
*** Ultrasound Division, Ceprano Hospital, Ceprano, Italy.



Fetal megacystis in the first-trimester is defined by a longitudinal bladder diameter of 7 mm or more or if bladder/CRL ratio is 13% or more.
According to Nicolaides (2004),  the longitudinal bladder diameter of 7–15 mm, signifies a 20% chance of a chromosomal defects, mainly trisomies 13 and 18.
Megacystis is associated with increased NT, which is observed in about 75% of those with chromosomal abnormalities, mainly trisomy 13, and in about 30% of those with normal karyotype (Liao et al 2003).

Case report

This is  the case of a 32-year-old woman at her first pregnancy. Her personal and family history were unremarkable. Her first ultrasound examination was performed at 8 weeks and reported to be normal, biometry was consistent with the length of the amenorrhea.

She was referred to our department for the first trimester ultrasound scan. The ultrasound was performed at 12 weeks of gestation. The CRL was 53 mm, which is normal for 12 weeks, BPD was 17 mm which was small for this gestation age.
NT was 2.9 mm (below the 99th centile - 3.5 mm). Fetus was of female sex.

  • Fetal head: flat face, microphtalmia, hypertelorism (in comparison with normal fetuses at the same gestational age).
  • Thorax: No apparent cardiac anomaly, mild hydrothorax

  • Subcutaneous edema

  • Reverse flow in the ductus venosus.
  • Megacystis and dilated urethra.

Chorionic villus sampling was offered to the patient. Patient preferred the termination of the pregnancy instead. The pregnancy was terminated within the next 3 days. The genetic testing was performed afterwards, the fetal karyotype showed Trisomy 13.

Images 1,2: Image 1 shows nuchal translucency, measuring 2.9 mm. Image 2 shows sagittal view of the thorax, arrow is pointing at the aorta.

Image 3,4: Image 3 shows hypertelorism. Image 4 shows an axial view of the fetal brain, no choriod plexus cyst is visible.

Images 5,6: Image 5 shows a four-chamber view. Arrow on image 6 indicates a small amount of pericardial fluid

Images 7,8: Image 7 shows a color Doppler of the four-chamber view. Image 8 shows a color Doppler of the pulmonary artery.

Images 9,10: Image 7 shows a reverse flow of the ductus venosus. Image 8 shows both kidneys, which seem hyperechogenic.

Images 11,12: Image 9 shows upper limbs. Image 10 shows a subcutaneous edema.

Images 13,14: Image 13 shows a female sex. Doppler imaging on image 14 shows both umbilical arteries along the dilated urinary bladder.

Images 15,16:
Sagittal view of the fetal abdomen showing the dilated urinary bladder, note the "keyhole" sign, caused by obstructed urethra.

Images 17,18,19: Images show a dilated bladder.


1. Kypros H. Nicolaides. The 11–13+6 weeks scan. 2004
2. Liao AW, Sebire NJ, Geerts L, Cicero S, Nicolaides KH. Megacystis at 10–14 weeks of gestation: Chromosomal defects and outcome according to bladder length.Ultrasound Obstet Gynecol 2003;21:338–41.

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