Becoming a mother is one of the most exciting times in an woman’s life. Most women will go to extreme lengths for their new baby to ensure that he or she is happy. There are different stages of pregnancy which are explained below
Pregnancy starts with Fertilization, the fusion of sperms and eggs usually occurring in the upper third of the Fallopian tube. Of the several hundred sperms released in the ejaculation, only a few thousand survive to reach the egg. Only one sperm will finally fertilize the egg. After fusing with the egg, that sperm triggers chemical changes in the outer membrane of the egg that prevents any other sperm from entering. After fertilization, the zygote is formed.
About a week after fertilization the zygote travels through the length of the fallopian tube and reaches the uterus, where it gets implanted on the uterine wall. Within a fortnight the one celled zygote divides into millions of cells and develops into an embryo
Stages in Pregnancy.
The period of time from fertilization to birth is generally divided into three trimesters, each about three months long.
The three embryonic tissue layer is formed during this period. Cellular differentiation begins to form organs during the third week. After one month the embryo is 5 mm long. At about 5 weeks the gestational sac can be seen on the ultrasound. At the end of the 6th week we can see the foetal pole and perhaps telltale signs cardiac activity in the embryo.
Beginning from eighth week, the sexually neutral fetus activates gene pathways for sex determination forming testes in XY or male fetuses and ovaries in XX or female fetuses.
At the end of the first trimester the baby is about 3.5 inches long. At this time, the placenta is formed and supplies the baby with oxygen from the mother’s blood supply and gets rid of the waste through mother’s blood system.
The fetus increases in size during this trimester and the bony parts of the skeleton is formed. Foetal movements can be felt by the mother. By 16-20 weeks may feel a fluttering that is the baby’s movement. By the 24th week the uterus will experience intermittent contractions and the doctor considers the fetus viable, which means half the babies born at this age do survive.
By 26-28th week the lungs in the baby are maturing. It is starting to store fat in the subcutaneous layer and its hair is growing. It can open its eyes as the fetus becomes increasingly more responsive to the world outside the womb.
By 32-33 weeks, baby’s fat deposits are starting to fill out. The lungs get matured in preparation for breathing. Fetal growth during this time uses large parts of the mother’s protein and calcium intake. Maternal antibodies pass to the fetus during the last month thereby conferring temporary immunity. From 36 weeks onwards the doctor considers the baby to be fully developed although there are organs like the nervous system which continue to develop till about 4 years of age.
The physiological changes during pregnancy call for extra nutrients and energy to meet demands of an expanding blood supply, the growth of maternal tissues, the developing fetus, loss of maternal tissues at birth and preparation of lactation. The increase in calorie requirement is around 300 kcal/day during the second and third trimesters and it farther increases to around 550 kcal/day during lactation.