Prenatal screening for congenital nephrosis

Antenatal screening for congenital nephrosis in Finland by maternal serum alpha-fetoprotein

In the Kuopio and North-Karelia districts of Finland 10724 pregnancies were screened for congenital nephrosis by maternal serum alpha-fetoprotein (AFP) measurement. Outcome was known for 10504 (98%) pregnancies, of which 509 (4 X 8%) had a serum AFP level greater than or equal to 2 X 5 multiples of the normal median (MoM) at 15-18 weeks gestation. After exclusion of those women who had a normal serum AFP level (less than 2 X 5 MoM) in a second sample, 'wrong dates' or multiple pregnancy, 267 (2 X 5%) remained with a high serum AFP level. Amniocentesis was carried out in 225 (2 X 1%) and 16 women had an amniotic fluid AFP level greater than 10 SD above the normal mean. In this group there were six fetuses with congenital nephrosis (four confirmed and two suspected), six other serious malformations (including an intrauterine death) and four without obvious abnormality. In the 98% pregnancies followed up there were no infants with congenital nephrosis that had been missed. Babies with congenital nephrosis require permanent hospitalization and have a mean survival of 8 months. In Finland, within certain areas, the birth prevalence is as high as 1 in 2600 per year. In such areas maternal serum AFP measurement appears to be a useful method of screening for congenital nephrosis. The service was also well accepted since 94% of the women with raised serum AFP levels wished to be screened again in a future pregnancy.

Renal pathology of fetal congenital nephrosis

In 15 fetuses with congenital nephrosis, distinct colloid-filled cystic tubular dilations were seen scattered in the renal cortex. Similar structures were not present in the controls. It is suggested that these structures are pathognomonic of congenital nephrosis in the fetus and make diagnosis possible even without electron microscopy.

Differential diagnosis of hydrops fetalis

Apart from isoimmunization, a number of conditions may present as hydrops fetalis and now account for a large proportion of hydropic infants. A large differential diagnosis must be considered when investigating the hydropic fetus and placenta while in utero, in the neonatal period, and at autopsy. An investigative protocol is proposed.