Embryo vs Fetus
Embryo and fetus are different stages in the human reproduction process. The human life starts when the sperm and ovum (egg) get together to form the fertilized ovum. Fertilized ovum starts to divide and produce more cells. When it starts to divide in to two cells, 8 weeks from fertilization, the period is called embryo period. The dividing cells collectively forms the embryo. The embryo rapidly divides and form the new organs and layers of the body. This is called embryo genesis. This is a critical period. When the embryo formed it may be in the fallopian tube. Then it will slowly moves towards the uterus and implanted in the uterine cavity. If embryo fails to move properly and implanted in the fallopian tube (or other than normal endometrium), then it will called as ectopic pregnancy. This is an emergency situation, and ruptured ectopic may cause death of the mother.
If the embryo implanted into the normal endometrial cavity of the uterus, this will grow. The placenta is formed to feed the embryo. During embryonic period, taking some drugs may harm the baby. These drugs are named Teratogenic drugs. The captopril (antihypertensive drug), tetracyclin, Vitamin A in high dose are some of the example. If you have doubt about the medicines you take during this period, you should consult your doctor before continuing or stopping the drugs. during the embryo period, most of the organs are formed but during foetal period, the mainly the growth of the organs occurs.
The fetal period starts from the 9th week from fertilization. The growth of the organs rapidly occurs during the period. The growth depends on the placental blood supply, the available space in the uterine cavity and the maternal nutritional status. Compromises in any of these factors will cause IUGR (intra uterine growth retardation) These babies are underweight at term.
Both embryo and fetus are the intra uterine babies.
The embryo is early stage of the development and the organs formed during this period.
The drugs may be teratogenic during the embryo period.
Fetus is the intra uterine baby, from 9th week of fertilization till delivery of the baby.
During the fetal period the organs grow rapidly.