Pregnancy is defined as the development of one or more offspring in the uterus or womb of a woman. Pregnancy undergoes many stages and these stages are arbitrarily grouped into three periods in humans. These periods are called trimesters. There are many events that take place in each trimester. The first trimester of pregnancy is when there is the greatest risk of a miscarriage. The second trimester of pregnancy is when the fetus or the baby inside the uterus can be more easily monitored. The third trimester of pregnancy is when the fetus becomes viable or can survive outside the uterus.
The human pregnancy has been extensively studied. Many experts say that the first event leading to pregnancy is fertilization. Fertilization is the meeting of the female ovum (egg) with the male spermatozoon (sperm) to unite and form the zygote. In layman’s terms, fertilization is known as conception. Fertilization naturally occurs after sexual intercourse but can be manipulated to occur in procedures such as artificial insemination.
Other factions say that pregnancy occurs after implantation. Implantation occurs when the zygote has become the blastocyst after rapid cell division. The blastocyst, upon reaching the uterus one week after fertilization, attaches itself to the innermost layer of the uterine wall called the endometrium. Pregnancy then proceeds and the blastocyst now become the embryo. At this time, structures that support the growth of the embryo such as the placenta and umbilical cord start to develop. Afterwards, the different cells of the embryo differentiate or grow into different precursor cells that will soon become the different organs and structures of the human body. Pregnancy then proceeds to the next step and the embryo will now become the fetus. The fetus continues to grow; now the growth is less of differentiation but more of development. The previously established cell lines continue to develop into the different organ systems of the body.
The human pregnancy usually lasts for forty weeks. The Naegele’s Rule is a formula based on the last normal menstrual period that computes for the expected date of birth. However, the pregnancy rarely lasts as long as the Expected Date of delivery. Pregnancy most often ends at 38 weeks. However, pregnancy is considered “full-term” at 37-42 weeks.
There are many changes that happen to a woman’s body during pregnancy, the most obvious of which is the enlarging abdomen. The fundic height or the height of the uterus as measured in centimetres from the pubic bone up to the fundus or topmost part of the uterus usually corresponds to the week of gestation or pregnancy weeks when the pregnancy is at 18 to 33 weeks. This usually alerts the obstetrician for abnormalities when the fundic height does not coincide with the week of pregnancy. An overly large uterus could mean a twin pregnancy and an overly small uterus could mean a fetal death.
Other changes include a darkening of the skin of the neck, face, underarms, and inguinal area. This is termed chloasma of pregnancy. This is due to the secretion of different hormones that the body needs to maintain the pregnancy. These changes usually resolve six months after the end of the pregnancy.