1. By: Carlos Daniel Caicedo & Carlos Eduardo Calle 10°c

2. What is Gestation? Gestation is when a female viviparous* animal carries an embryo* or fetus. The interval time of a gestation plus two weeks is called gestation period*. The length of time plus two weeks that the offspring have spent developing in the uterus is called gestational age*.

3. In mammals the gestation period is the period in which the fetus develops, this starts with the fertilization and ends on the birth. Smaller species normally have a shorter gestation period than larger animals: An example is the gestation period of a cat it normally takes 58–65 days while an Elephant's gestation period lasts 645 days. What is gestation period?

4. In humans the gestation period is normally of nine months. Factor such as gender can affect the duration of the gestation period, for us humans a male fetus tends to gestate longer than female fetuses and multiple pregnancies, tend to take a shorter time. The ethnicity (race) make the gestation period longer or shorter.

5. Gestational age Gestational age is the time measured from the first day of the woman's last menstrual cycle to the date were the baby is born, it is measured in weeks. A normal pregnancy can range from 38 to 42 weeks. Infants born before 37 weeks are considered premature. Infants born after 42 weeks are considered post mature. You can determine the gestation age in two ways, before or after the baby is born: Before birth, growth is determined with ultrasound by measuring the size of the head, and abdomen.

6. After the birth, it can be determined by measuring the babys head circumference, the babys height, condition of skin and hair, reflexes, muscle tone, posture, and vital signs. Finding the gestational age is really important because with this doctors can gather valuable information of expected or potential problems that the baby could have.

7. After a female egg is fertilized, the resulting one celled organism is called zygote. Once the egg is fertilized, the zygote begins a two week period of rapid cell division and becomes to be a embryo. The zygote divides with the process of mitosis, in witch each cell doubles by dividing in two cells. This two week period is called the germinal period of development. Whats a zygote?

8. A zygote is a single diploid cell(a diploid cell is cell with two chromosomes), created through the merging of two haploid cells (a cell that contains a complete set of chromosomes). The period of the zygote lasts for about four days. Around the fifth day, the mass of cells becomes known as a blastocyst (the blastocyst is a structure formed in the early embryogenesis of mam mals). The germinal period will last for fourteen days, after this the embryonic period begins.

9. Whats a embryo? An embryo is an organism in the early stages of development which cannot survive on its own. The precise definition of an embryo varies; in humans, for example, a fertilized egg may be considered an embryo until around the eighth week of pregnancy, as the embryo mature it starts to turn into a recognizable form to the point when people start referring to it as a fetus, especially in humans.

10. The term “embryo” is only used to refer to eukaryote (or muticellular organisms) organisms. The formation of an embryo starts at fertilization, when eggs and sperm meet, they form what is known as a zygote. After fertilization, the zygote starts to divide, when division begins the zygote turns into an embryo.

11. Multiple gestations Occurs when two or more fetuses are conceived at the same time in the same woman. With multiple gestation, the fetuses are either monozygotic* or dizygotic*. There is a higher rate of occurrence with use of fertility drugs or treatments, such as in vitro fertilization.

12. Monozygotic: during conception, the sperm fertilizes one egg, which will later split into two or more developing embryos. Dizygotic multiples: occur when a woman’s body releases several eggs, and those eggs are each fertilized by different sperm. The resulting fetuses are fraternal siblings, and are not identical.

13. Social factors which affect gestation Medications and drugs can also impact embryonic growth. This 8,000 babies were born with birth defects because their mothers had taken the tranquilizer Thalidomide. Some races are more prone to teen pregnancy, data taken by “The Guttmacher Institute ” show that: blacks typically have 126 teen girls become pregnant in every 1,000 girls. Hispanic have 127 teen girls become pregnant in every 1,000 girls. Non-Hispanic whites average 44 pregnancies per 1,000 girls.

14. Today researches show that a girl who lives in poverty is more likely to become pregnant because of teachings and attitudes on sex, as well as access to contraception.

15. Enviromental factors which affect gestation Researchers found that the air quality of the area was worse during the winter months, and the infants conceived during those winter months saw the most intrauterine growth retardation. Smoking during gestation cause aproximately 20 to 30 percent of low-birth weight babies. Reaserches states that up to 14 percent of preterm deliveries are due to smoking.

16. FAQ What is the difference between a pregnancy and gestation? Pregnancy is the fertilization and development of the offspring in womans uterus, while gestation is the carrying of the embryo. Why do all animals have a different gestation period? For most species, the amount a fetus grows before birth determines the length of the gestation period. Smaller species normally have a shorter gestation period than larger animals.

18. Bibliography http://www.wisegeek.com/what-is-a-multiple- gestation.htm http://www.wisegeek.com/what-is-a-multiple- gestation.htm http://www.livestrong.com/article/233087- environmental-factors-affecting-fetus- development/#ixzz1mUNd5K86 http://www.livestrong.com/article/233087- environmental-factors-affecting-fetus- development/#ixzz1mUNd5K86 http://multiples.about.com/od/twinpregnancyfaq/f/t winpregnancy_f.htm http://multiples.about.com/od/twinpregnancyfaq/f/t winpregnancy_f.htm http://www.answers.com/topic/embryo