Germinal Stage-
Takes place in the first two weeks, between conception and the implantation of the embryo.
The organism is called a zygote.
The zygote divides into two cells, then continues to divide into several more cells as it travels to the uterus. The zygote takes 3 to 4 days to to implant in the uterine wall. Implantation takes another week or more. After a few days from implantation, the cell mass forms into a blastocyst. The blastocyst, made of 60-100 cells, begin to separate into groups, forming structures. The blastocyst forms two layers, one layer will become the embryo. The outer layer becomes four membranes. One will nourish and protect the the embryo, the second produces blood cells until the liver develops, the third develops into the umbilical cord and blood vessels, and the fourth becomes the amniotic sac.
The blastocyst looks like a balloon with a bunch of little balls squished inside of it.
The germinal stage takes place in the first two weeks.
Risks: an ectopic pregnancy could occur when the implantation occurs in the fallopian tube. Prenatal exposure to lead, mercury and zinc can cause a baby to have cognitive delays, and low birth weight.
Embryonic stage-
The organism is called an embryo
Development follows cephalocaudal (head to tail) and proximodistal (inner to outer). The head grows larger than the body and the organs nearest the spinal cord grow earlier than the extremities. The ectoderm (outer layer of the cells) develop into the nervous system, sensory organs, anils, hair, teeth and out layer of skin. The endoderm (inner layer) develops the digestive and respiratory systems, liver an pancreas. The third middle layer, mesoderm, than develops the excretory, reproductive , and circulatory systems, muscles, skeleton and inner layer of the skin. In the third week of development, the embryo's heart begins to beat. The major organs, arms, and legs have now began develop by the end of the first and second month. Around the 7th week the sex organs begin to differentiate. If the Y chromosome is absent, the ovaries begin to differentiate. The placenta is mass of tissue that connects by the umbilical cord from the mother to the baby to supply nutrients and exchange waste.
At this stage the embryo is about 1 inch long and now looks like a human.
Takes place 2 to 8 weeks after fertilization.
Risks: The embryonic stage is the most at risk because that is when the babies organs and neural tubes begin to develop. A blighted ovum is the most common form of miscarriages at this stage. A blighted ovum pregnancy occurs when the fertilized egg is not able to develop into an embryo. It is very important to take folic acid, avoid smoking, taking drugs, and drinking alcohol, as this can cause miscarriages. The heart is also most vulnerable during this stage to certain teratogens. This stage in pregnancy is most vulnerable because the embryos organs begin to differentiate therefore they are most vulnerable to teratogens at this stage.
Fetal Stage-
The organism is called a fetus.
During this stage, the baby can make movements now in response to external stimulation. The fetus can now suck it's thumb, and open and close it's eyes. Around the 13th week, the fetus can hear sound waves. By month 7, the fetus can do somersaults and the mother will begin to feel like she is getting kicked and punched from inside. Then as the fetus gets larger and birth approaches, the fetus will turn so it's head is down and ready for delivery. The mother will feel less and less of the fetus's movements as it gets bigger and there is less space for it to move around. Chances of survival by month 7 are 90% and even greater in the 8th month.
The baby now has all 10 fingers and toes and has grown four to five times it's length from 3 inches to 14. By the end of the 6th month, the fetus has gained about 5 1/2 pounds.
The fetal stage lasts from the beginning of the third month until birth.
Risk: Gestational diabetes, incompetent cervix, preeclampsia, placenta previa, are all risks the mother can face during this stage. If a mother does not control her blood sugar, she can have difficulties during birth and the baby may be born with abnormal blood sugars. An incompetent cervix can cause the cervix to become softer and weaker leading to early delivery which could result in a miscarriage. Preeclampsia is caused by high blood pressure that can lead to early delivery and sometimes fatal complications to the mother and baby, if left untreated. Smoking can enhance risks of placenta previa, causing the placenta to detach and block the opening to the cervix, not allowing the baby to move into the birth canal for delivery.