Amniotic fluid is mainly produced by:
Placenta
Fetus
Chorion
Amnion
“The precise origin of the amniotic fluid remains is still not well understood. It is probably of mixed maternal and fetal origin.”
Dutta Obs. 8/e, p 43
But this cannot help us to solve this question.
Let’s see what Williams Obs. has to say on Origin of Amniotic fluid.
“In early pregnancy, amniotic fluid is an ultrafiltrate of maternal plasma. By the beginning of second trimester, it consists largely of extracellular fluid which diffuses through the fetal skin, and thus reflects the composition of fetal plasma”.
After 20 weeks, however, the cornification of fetal skin prevents this diffusion and amniotic fluid is composed largely of fetal urine.”
Williams Obs. 23/e, p 88, 89
Reading the above text, it can be concluded that in early pregnancy - Mother is the main contributor whereas during rest of the pregnancy - Fetus is the main contributor.