Nutrient and waste requirements for the developing fetus are handled during the first few weeks by:
the placenta
diffusion through the endometrium
the chorion
the blastocyst

diffusion through the endometrium

Explanation:

During the first weeks after egg implantation, its nutrition will depend on trophoblastic digestion and endometrial phagocytosis, ie the nutrient and residue requirements for the developing fetus are treated during the first weeks by diffusion through the endometrium. However by the 12th week of pregnancy, the placenta has developed sufficiently so that it can thereafter supply all the necessary nutrients.

Nutrients diffuse from the maternal blood through the placental villus membrane into the fetal blood, through the umbilical vein through the fetus. In turn, fetal excreta such as carbon dioxide, urea and other substances diffuse from fetal blood into maternal blood and are eliminated outward by the mother's excretory functions.

this is math not biology xd