The 11-14-week scan

The fetal kidneys and adrenals can first be visualized by transabdominal ultrasound at 9 weeks and they are seen in all cases from 12 weeks¹⁸. The renal echogenicity is high at 9 weeks but decreases with gestation; the adrenals appear as translucent structures with an echodense cortex¹⁸. The fetal bladder can be visualized in about 80% of fetuses at 11 weeks and in more than 90% by 13 weeks⁷⁵. At 12–13 weeks, the fetal kidneys can be visualized in 99% of the cases, by using both transabdominal and transvaginal sonography⁴⁹.

Bilateral renal agenesis

This sporadic condition, with a birth prevalence of about 1 in 4000, is usually diagnosed in the second trimester of pregnancy by the findings of anhydramnios, absence of the urinary bladder and failure to identify the fetal kidneys; the differential diagnosis is preterm prelabor rupture of membranes and severe uteroplacental insufficiency that may also present with oligohydramnios.

Bronshtein et al. reported the prenatal diagnosis of bilateral renal agenesis at 14 weeks of gestation in five fetuses; in all cases, there were hypoechogenic masses in the renal beds, that were subsequently found at pathological examination to be enlarged adrenals⁷⁶. The amniotic fluid volume was normal in all cases at 14 weeks. In two cases, a cystic structure suggestive of the fetal bladder was temporarily detected in the fetal pelvis but this disappeared by 16–17 weeks.

Infantile polycystic kidney disease

This an autosomal recessive condition with a birth prevalence of about 1 in 50 000. It is subdivided into perinatal, neonatal, infantile and juvenile types, on the basis of the age of onset of the clinical presentation and the degree of renal involvement. Prenatal diagnosis by ultrasound is confined to the perinatal and probably the neonatal types and is based on the demonstration of bilaterally enlarged and homogeneously hyperechogenic kidneys. While there is often associated oligohydramnios, this is not found invariably. These sonographic appearances, however, may not become apparent until 26 weeks of gestation, and therefore serial scans should be performed for exclusion of the diagnosis.

Bronshtein et al. reported a case of infantile polycystic kidney disease; at 11 and 15 weeks, the kidneys and bladder looked normal, but at 28 weeks there was oligohydramnios with bilaterally enlarged and diffusely hyperechogenic kidneys⁷⁷. Retrospective examination of the videotapes taken from the early scans demonstrated that the kidneys were of increased echogenicity and increased length from as early as 12 weeks.

Multicystic dysplastic kidney disease

In this sporadic condition, which may be unilateral or bilateral, the collecting tubules and nephrons are dysplastic. The collecting tubules become cystic and the diameter of the cysts determines the size of the kidneys, which may be large and multicystic or small, shrunken and hyperechogenic. Occasionally, only one of a small number of adjacent collecting tubules is involved so that only a segment of the kidney is abnormal. With bilateral involvement, there is associated absence of the bladder and oligohydramnios.

Cullen et al. reported a case that at 11 weeks demonstrated hyperechoic kidneys with no obvious dilatation of the bladder; ultrasound examination in the newborn, after delivery at term, confirmed the diagnosis of cystic dysplastic kidneys²⁵. Bronshtein et al. reported a case with a unilateral multicystic kidney diagnosed at 12 weeks during routine ultrasound examination; the fetal karyotype was normal⁷⁸. Ultrasound examination of the newborn confirmed the antenatal diagnosis.

Screening studies

In a screening study involving ultrasound examinations at 11–14 weeks of gestation and at 18–20 weeks in 3991 patients, there were three cases of unilateral multicystic dysplastic kidneys and none was detected at the early scan; two were diagnosed at 18–20 weeks and the third was detected at 31 weeks²⁶. In another screening study involving 1632 pregnancies at 12–14 weeks, there was one case with unilateral multicystic kidneys and this was correctly identified in the first-trimester scan³⁵.

Hydronephrosis

Varying degrees of pelvicalyceal dilatation are found in about 1% of fetuses. Mild hydronephrosis or pyelectasia may be due to relaxation of smooth muscle of the urinary tract by the high levels of circulating maternal hormones, or maternal–fetal overhydration. In the majority of cases, the condition remains stable or resolves in the neonatal period. In about 20% of cases, there may be an underlying ureteropelvic junction obstruction or vesicoureteric reflux that requires postnatal follow-up and possible surgery. Moderate or severe pelvicalyceal dilatation is usually progressive and, in more than 50% of cases, surgery is necessary during the first 2 years of life.

Screening studies

In an ultrasound screening study of 622 high-risk pregnancies at 10–13 weeks, there were two cases of hydronephrosis and exomphalos and they were both detected at the first scan; one pregnancy was terminated and the other resulted in a livebirth with cloacal defect as well as the exomphalos²⁵. In a screening study involving ultrasound examinations at 11–14 weeks of gestation and at 18–20 weeks in 3991 low-risk patients, there were four cases of hydronephrosis and only one of these was diagnosed at the early scan²⁶.

Megacystis

Sebire et al. examined transabdominally 300 pregnancies at 10–14 weeks of gestation and reported a significant increase in bladder length with crown–rump length (Figure 13), but, within this gestational age range, none of the measurements was more than 6 mm⁷⁹. The fetal bladder was always visualized if the crown–rump length was more than 67 mm, but not in 9% of those with a crown–rump length of 38–67 mm.

Bulic et al. described a 14-week fetus with megacystis (bladder length 50 mm) and oligohydramnios; pathological examination after termination at 15 weeks showed urethral atresia, hypertrophic bladder, dysplastic kidneys and absence of abdominal musculature⁸⁰. In another 11-week fetus, there was megacystis (20 mm); at 14 weeks there was enlargement of the bladder and oligohydramnios. Pathological examination after termination demonstrated urethral atresia, severe megacystis but normal kidneys⁸⁰.

Stiller reported an 11-week fetus with megacystis (10 mm) but normal kidneys and amniotic fluid⁸¹. At 13 weeks, there was enlargement of the bladder (30 mm) and bilateral hydronephrosis with reduced amniotic fluid; the pregnancy was terminated.

Drugan et al. reported a 12-week fetus with megacystis (18 mm); at 14 weeks there was further enlargement of the bladder with normal kidneys but oligohydramnios⁸². Vesicoamniotic shunting was carried out and the pregnancy continued normally; a male infant with mild prune-belly and moderate renal function (40–50%) was born at 35 weeks.

Zimmer and Bronshtein reported an 11-week fetus with megacystis (13 mm) and two umbilical cord cysts⁸³. At 12 weeks, the bladder increased (30 mm) and there was evidence of hydronephrosis; at 13 weeks there was intrauterine death. In another 12-week fetus, there was megacystis (46 mm), bilateral hydronephrosis, increased nuchal translucency and talipes. Chorionic villus sampling showed Turner mosaicism and the pregnancy was terminated.

Yoshida et al. reported a 13-week fetus with megacystis (45 mm) and decreased amniotic fluid volume; follow-up scans demonstrated resolution of the megacystis and normalization of the amniotic fluid volume⁸⁴. At 28 weeks, tetralogy of Fallot was diagnosed. Investigations after delivery at 38 weeks confirmed the cardiac defect and, in addition, demonstrated vaginal atresia, imperforate anus, recto-urethral fistula, bilateral vesicoureteral reflux, unilateral renal hypoplasia, hypoplasia of abdominal muscles, scoliosis and bilateral talipes. The karyotype was normal female. The suggested diagnosis was VACTERL-like association.

Fried et al. reported a 13-week fetus with megacystis (30 mm); a repeat scan 2 days later demonstrated urinary ascites with a thick-walled deflated bladder and the pregnancy was terminated⁸⁵. The fetal karyotype was 46,XY.

Hoshino et al. reported a fetus with normal sonographic appearance at 10 weeks but, at 12 weeks, there was megacystis (40 mm) with normal amniotic fluid volume; at 13 weeks, the diameter of the bladder increased to 54 mm, there was bilateral hydronephrosis and the amniotic fluid volume was reduced⁸⁶.

Cazorla et al. reported a fetus with normal sonographic appearance at 8 weeks but, at 13 weeks, there was megacystis (33 mm) and reduced amniotic fluid volume; the fetal karyotype was 46,XY⁸⁷. At 16 weeks, the fetus developed generalized edema and the pregnancy was terminated. Pathological examination revealed urethral atresia, megacystis, hydronephrosis and atrophied abdominal muscles.

Screening studies

In an ultrasound screening study of 622 high-risk pregnancies at 10–13 weeks, there were two cases with urethral obstruction presenting as megacystis at 11 and 13 weeks of gestation²⁵. In a screening study for chromosomal abnormalities by assessment of fetal nuchal translucency thickness, 24 492 singleton pregnancies were examined⁷⁹. Megacystis was present in 15 fetuses (prevalence of 1 in 1633) and, in these cases, the longitudinal bladder diameter was 8–32 mm. There were three cases with chromosomal abnormalities and two of these had increased nuchal translucency thickness. In the chromosomally normal group with mild-to-moderate megacystis (longitudinal bladder diameter of 8–12 mm), the majority of fetuses had spontaneous resolution without any obvious adverse effects on renal development and function. In those with severe megacystis (minimum longitudinal bladder diameter of 17 mm), there was evolution to obstructive uropathy and renal dysplasia⁷⁹.