Urinary bladder can be detected by sonography as an oval anechoic structure in the fetal pelvis, surrounded by the umbilical arteries, from 10 weeks of gestation [1], [2], [3]. Fetal megacystis is a sonographic sign encountered in 1 in 1500 pregnancies, and defined in first trimester as a bladder with longitudinal bladder diameter (LBD) of 7 mm or more (Fig. 1) [1,4,5].

Several authors have studied the role of LBD in the presumption of megacystis etiology and its association with fetal outcomes [2,[4], [5], [6]]. Low urinary tract obstruction (LUTO) is usually described as the main cause for fetal megacystis, especially in fetuses with LBD higher than 15 mm [1,7,8]. In these cases, hydronephrosis, renal dysplasia and oligohydramnios are common and linked to poor prognosis [1,5]. On the other hand, there is no consensus regarding the association between LBD and aneuploidies, but it also seems to heighten its risk, especially for trisomy 13 and 18 [4,7]. In these cases, other fetal malformations are usually present, such as ventriculomegaly or omphalocele [4,7,9]. Other congenital and genetical syndromes may also be associated with megacystis, including anorectal malformations and overgrowth syndromes [1]. If diagnosed prenatally, these cases commonly end in pregnancy termination [1,10].

Still, not all fetuses with megacystis have poor prognosis, such as isolated megacystis cases that resolve spontaneously during second trimester [10]. Almost all of these have an LBD of 15 mm or less and seem to have excellent prognosis, without severe postnatal urinary problems [4,5].

There is still no standardized management for fetal megacystis [1]. Invasive genetic testing is crucial for work-up of fetuses with other malformations or aneuploidy markers. However, there has not been a consensus about how to manage cases with isolated megacystis, especially if they resolve spontaneously. Thus, counseling is still controversial [9,10].

The aim of this study is to evaluate the association between LBD and the etiology, management and outcomes of fetuses diagnosed with megacystis during first trimester. We also aimed to describe other parameters concerning prenatal screening of megacystis cases.