PREGNANCY AND CONCEPTION
There are several stages in pregnancy and conception; a lot of divisions will take place, as well as millions of sperm cells will die for the goal of reaching their destination --- the egg (ovum). In the long run, only one spermatozoon or sperm cell among an approximately 400 million sperm cells released each ejaculation will be successful in the goal of penetrating the coated ovum and fertilizing it. Such incidence of the union of the spermatozoon and the ovum is the beginning of pregnancy --- the stage called fertilization, or otherwise known as conception, impregnation, or fecundation.
The functional life of a spermatozoon is 48 hours, possibly as long as 72 hours. As such, 72 hours is the critical time on which fertilization should occur (48 hours before ovulation and 24 hours afterwards). The ovum, if not fertilized within 24 hours after ovulation or after it has been released, will also disintegrate. When this happens, fertilization can’t take place as well. Hence, comes the importance of right timing of ovulation and sexual intercourse.
Immediately after penetration of the spermatozoon (sperm cell) to the ovum (egg cell), their chromosomal materials will fuse. The resulting structure of such fusion is called a zygote. The spermatozoon and the ovum each contain 23 chromosomes (22 autosomes and 1 sex chromosome). With this, a fertilized ovum will have 46 chromosomes. If an X-carrying chromosome enters the ovum, the resulting child will have two X chromosomes and will be female (XX). However, if a Y-carrying chromosome enters the ovum, the child will be female with an X and Y chromosomes (XY).
Fertilization, as described above might seem to flow smoothly and hassle-free, but in reality it isn’t that easy to achieve. For fertilization to occur, at least three factors must be met: the maturation of both sperm and ovum, the ability of the sperm to reach the ovum and the ability of the sperm to penetrate the zona pellucida (the membrane surrounding the ovum) and cell membrane.
From the zygote, which is the fertilized ovum, the future child together with the accessory structures needed for it to survive the intrauterine life such as the placenta, fetal membranes, amniotic fluid and umbilical cord are all formed.
Once the zygote becomes a blastocyst which will be around 8 to 10 days after fertilization, implantation or the contact between the growing structure (blastocyst) and the endometrium (inner lining of the uterus) will occur. A common sign for this stage is the presence of a small amount of vaginal spotting which can be mistaken as a menstrual period. Once implanted, the zygote is called an embryo.
The developing baby is called an embryo from the moment of conception to the eighth week of pregnancy. After the eighth week and until the moment of birth, the developing baby is called a fetus.
In a nutshell, in just 38 weeks, a fertilized egg matures from a single cell carrying all the necessary genetic material to a fully developed fetus ready to be born.