Placental villitis at the bottom is seen in conjunction with hydropic change at the top in this placenta with congenital cytomegalovirus (CMV) infection. Both of these microscopic changes can occur together. Congenital infection is a common cause for hydrops fetalis.
http://library.med.utah.edu/WebPath/PLACHTML/PLAC083.html
Hydrops fetalis is a condition in the fetus characterized by an accumulation of fluid, or edema, in at least two fetal compartments. By comparison, hydrops allantois or hydrops amnion are an accumulation of excessive fluid in the allantoic or amniotic space respectively.
https://en.wikipedia.org/wiki/Hydrops_fetalis
Non-immune hydrops can also be unrelated to anemia, for example if a fetal tumor or congenital cystic adenomatoid malformation increases the demand for blood flow. The increased demand for cardiac output leads to heart failure, and corresponding edema.
https://en.wikipedia.org/wiki/Hydrops_fetalis
1 Thick placenta. 2  Thick placenta may be found in maternal diabetes mellitus, Rh immunization, non-immune hydrops or in normal pregnancies. 3  Thin placenta. 4  Pregnancies with non-immune hydrops complicated by IUGR, pre-eclampsia or diabetic angiopathy may result in a thin placenta.
http://www.fetalultrasound.com/online/text/36-029.htm
1 Thickened subcutaneous tissues (anasarca macrosomia (excessive fat in the subcutaneous layer of a fetus of a diabetic mother). 2  Thick placenta. 3  Thick placenta may be found in maternal diabetes mellitus, Rh immunization, non-immune hydrops or in normal pregnancies.
http://www.fetalultrasound.com/online/text/36-029.htm
The edema is usually seen in the fetal subcutaneous tissue, sometimes leading to spontaneous abortion. It is a prenatal form of heart failure, in which the heart is unable to satisfy its demand for a high amount of blood flow.
https://en.wikipedia.org/wiki/Hydrops_fetalis
Hydrops fetalis usually stems from fetal anemia, when the heart needs to pump a much greater volume of blood to deliver the same amount of oxygen. This anemia can have either an immune or non-immune cause.
https://en.wikipedia.org/wiki/Hydrops_fetalis
1 Thick placenta may be found in maternal diabetes mellitus, Rh immunization, non-immune hydrops or in normal pregnancies. 2  Thin placenta. 3  Pregnancies with non-immune hydrops complicated by IUGR, pre-eclampsia or diabetic angiopathy may result in a thin placenta.
http://www.fetalultrasound.com/online/text/36-029.htm
1 Thin placenta. 2  Pregnancies with non-immune hydrops complicated by IUGR, pre-eclampsia or diabetic angiopathy may result in a thin placenta. 3  Polyhydramnios may also result in thinning of a normal or thick placenta. 4  Hepatomegaly-Table of normal liver length. 5  Polyhydramnios or oligohydramnios.
http://www.fetalultrasound.com/online/text/36-029.htm
Hydrops of the placenta, as shown here, almost always accompanies fetal hydrops. Causes for fetal hydrops may include fetal anemia, fetal cardiac disease, congenital anomalies, and congenital infections, but there are a multitude of potential causes for hydrops.
http://library.med.utah.edu/WebPath/PLACHTML/PLAC029.html
what may cause a hydropic placenta
Congenital infection may cause a hydropic placenta.  Congenital infection may cause a hydropic placenta.  