Living entities exhibit a fundamental characteristic through which they produce new offspring by transferring genetic information which involves mating two individuals from the opposite gender. It is termed sexual reproduction and is the most significant and advanced form of reproduction exhibited by higher animals including humans. Due to its complexities, the length of human pregnancies can intrinsically vary by as much as 3-4 weeks.
Gestation Period
The normal duration it takes for the development of the fetus from the time of fertilization in the womb of its mother is called the gestation period. In humans, the gestation period is for about 9 months or approximately 280 days. It is calculated from the incipience of their last menstrual period. As per studies, a mere 4% of women deliver in this duration and around 68%-70% deliver within 10 days of their estimated due date. As per recent research, the average time from ovulation to birth was found to be about 38 weeks and two days – 268 days.
However, this length of the pregnancy was said to be varying by about 37 days. The length of gestation in women may vary due to factors such as errors in the authorization of gestational age. Without the inclusion of these factors, a variability of nearly 5 weeks was still observed.
Foetal Development
In the first 4 weeks post-fertilization, the umbilical cord, the brain and the heart is formed and the heart starts to beat. In the next week(Week 5), the internal organs and the limbs begin to take shape.
The sixth week into the conception, the eyes of the embryo become visible and the formation of other sense organs such as the ears, mouth and nose takes place. After 8 weeks of fertilization, the face looks more human-like, the tail goes invisible, the embryo exhibits its gender through its respective sex organ( testes or ovaries), major organs of the body are formed and the cartilage is replaced by the bone. From this stage onwards, the embryo is addressed as the fetus. Three months after the process of fertilization, the following events occur:
- Limb movement is coordinated by the muscles and nerves.
- The cartilage is continuously replaced by the growth of the bones
- Formation of the milk teeth
- Baby starts kicking and thumb-sucking
- Clear formation of external sex organs
- The amniotic fluid is taken in by the fetus into its mouth. It releases faeces and urine into the amniotic fluid
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Related Links:
| Embryology |
| Embryo Development |
| Fertilization And Implantation |
| Fertilization – Internal And External Fertilization |
| Menstrual Cycle – Reproductive Phase In Humans |
Frequently Asked Questions on Human reproduction
What is gestational age?
Gestational age is the time period between a pregnant woman’s last menstrual period and till present. It is measured in weeks.
What is blastula and blastocyst?
The tropoblast cells in the morula stage secrete a fluid called blastocoel. Now the morula is converted into blastula. In mammals, blastula is termed a blastocyst due to the different nature of surface layer and inner cell mass.
What is morula?
The 16 cell stage of embryo after fertilization is called morula. It undergoes compaction to form flat cells in the outer layer and round cells inside.
What is gastrulation?
The formation of gastrula is called gastrulation. The primary germinal layers namely endoderm, ectoderm and mesoderm are formed during gastrulation.
What is implantation?
The attachment of the embryo with the uterine endometrium is known as implantation.
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