Gestation From fertilization to birth Trimesters Gestation is

Gestation From fertilization to birth

Trimesters � Gestation is divided into 3 trimesters ◦ 1 st trimester: week 1 – week 13 ◦ 2 nd trimester: week 14 – week 26 ◦ 3 rd trimester: week 27 – week 40

Zygote to Embryo � At the time of fertilization the spermatozoa and ovum create a one cell zygote. � As it travels down the fallopian tube it undergoes a series of cell divisions ◦ 2 cell div. � The 4 cell div. 8 cell div. 16 cell division cells reaches the uterus in the shape of a fluid filled ball containing a group of cells called the embryoblast ◦ The outside layer becomes the placenta ◦ The embryoblast becomes the embro

Formation of the Placenta � 2 important tissues form between day 10 and 14 1. Amnion – develops into the amniotic sac which contains the embryo and the amniotic fluid. Amniotic fluid protects the embryo from shock. 2. Placenta carries oxygen and nutrients to the fetus from the mother through the umbilical cord.

Prenatal Development � Conception—when a sperm penetrates the ovum � Zygote—a fertilized egg � Germinal period—first two weeks after conception � Embryonic period—weeks three through eight after conception � Fetal period—two months after conception until birth

8 week embryo

12 week fetus

18 week fetus

20 weeks (5 months)

24 weeks (6 months)

28 weeks (7 months)

32 weeks (8 months)

In-Class assignment! � Complete the chart to outline the different organs that are developing as the pregnancy develops. � Include the size of the fetus. � Include the risks to the fetus that can occur during that period of development. � Text book pg. 262 -267

Prenatal influences on development � Nutrition � Anxiety � Mother’s general health � Maternal age � Teratogens—any agent that causes a birth defect (e. g. , drugs, radiation, viruses) � Disease