PSYC 352 @ UCalgary
Fall Semester 2026
Unit One: Prenatal Development
Week One: Sept 1st – 4th
- Stages of Pregnancy From Two Perspectives
o From a medical perspective, the period of ovulation is
considered part of the pregnancy cycle. Since ovulation
usually occurs about two weeks before conception, a
person is already considered two weeks pregnant by the
time conception occurs. As a result, pregnancy is said to
last about 40 weeks.
Pregnancy itself is divided into three trimesters
First trimester
Second trimester
Third trimester
o In contrast, when pregnancy is measured from the
offspring’s perspective, counting begins at the moment of
conception. As a result, pregnancy for the offspring is
said to last about 38 weeks.
The offspring passes through three stages during
pregnancy:
Zygote
o Fertilization occurs in the fallopian tubes,
while implantation occurs in the uterus.
o Timeline of Fertilization:
24–30 hours after fertilization, the
chromosomes combine.
At 36 hours, the zygote divides into
two cells.
At 48 hours, it divides further into
four cells.
At 3 days, it has 16–32 cells.
At 4 days, it becomes a blastocyst of
about 100 cells.
o Timeline of Implantation:
Fall Semester 2026
Unit One: Prenatal Development
Week One: Sept 1st – 4th
- Stages of Pregnancy From Two Perspectives
o From a medical perspective, the period of ovulation is
considered part of the pregnancy cycle. Since ovulation
usually occurs about two weeks before conception, a
person is already considered two weeks pregnant by the
time conception occurs. As a result, pregnancy is said to
last about 40 weeks.
Pregnancy itself is divided into three trimesters
First trimester
Second trimester
Third trimester
o In contrast, when pregnancy is measured from the
offspring’s perspective, counting begins at the moment of
conception. As a result, pregnancy for the offspring is
said to last about 38 weeks.
The offspring passes through three stages during
pregnancy:
Zygote
o Fertilization occurs in the fallopian tubes,
while implantation occurs in the uterus.
o Timeline of Fertilization:
24–30 hours after fertilization, the
chromosomes combine.
At 36 hours, the zygote divides into
two cells.
At 48 hours, it divides further into
four cells.
At 3 days, it has 16–32 cells.
At 4 days, it becomes a blastocyst of
about 100 cells.
o Timeline of Implantation:
