The product of fertilization in sexually-reproducing organisms like humans is the ZYGOTE which develops into embryo and gets implanted in the uterus/womb of the female where it undergoes growth. The uterus of a female is designed to cater for the developing foetus's needs e.g nutrients, excretion, etc as mentioned in the question.
Renee, being pregnant for the first time wonders how this happens. It occurs through an organ unique to mammals called PLACENTA. Placenta serves as a connection point between the mother and the fetus. The placenta helps the mother to internally pass usable nutrients and oxygen to the fetus and also transfer waste products from the fetus to the mother's blood. Since, the fetus cannot yet derive these life-dependent substances itself, the mother transfers them to it through the placenta.
Therefore, Reene need not wonder because the placenta in her uterus helps do the job.
