To determine the method and clinical value of standardized first-trimester ultrasonographic diagnosis of single fetal megacystis in singleton pregnancy.

A total 16 586 cases of singleton pregnancy at gestational age between 11-13^{+ 6} weeks were scanned in our hospital by color Doppler ultrasound according to the standardized prenatal ultrasound from Jan 2009 to April 2016. Fetal bladder was defined by showing two umbilical arteries and the size of the bladder was measured. Cases of fetal megacystis diagnosed in first-trimester were followed sonographically and clinical outcomes were recorded.

Totally eight cases of fetal megacystis were detected. Fetal karyotyping was performed in five cases, among which four cases had normal karyotype and one case was confirmed as trisomy 18. Thickened nuchal translucency (NT), mid gut herniation, excessively flexed right wrist joint and absence of fetal stomach were associated anomalies detected in first trimester ultrasound. Follow-up second-trimester ultrasound also found associated anomalies including congenital heart disease, hydronephrosis and anhydramnios. Terminal of pregnancy was performed in three cases in early pregnancy. One case of spontaneous fetal death occurred at gestational age of 15 weeks, and the other four cases of pregnancy were terminated in mid-trimester. Autopsy was performed in four aborted fetuses, which revealed two cases of prune belly syndrome, one case of urethral atresia and one case of posterior urethral valve.

It will effectively detect and diagnose fetal megacystis during early pregnancy with standardized prenatal ultrasound. Fetal megacystis detected in early pregnancy has poor outcome.