"He makes you, in the wombs of your mothers, In stages, one after another, In three veils of darkness." [Al-Quran 39:6]
According to Prof. Keith Moore these three veils of darkness in the Quran refer to:
(i) Anterior abdominal wall of the mother
(ii) The uterine wall
(iii) The amnio-chorionic membrane
(from "The Quran and Modern Science, Compatible or Incompatible?" by "Dr. Zakir Abdul Karim Naik" published by Darussalam)