Conception refers to the process by which the sperm fuses with the ovum in the in the fallopian tube to form a viable zygote. Conception, also referred to as fertilization occurs during ovulation. Every human being results from a single cell when the sperm fertilizes the ovum.

Fertilization and implantation

After fertilization, the single cell goes through a process of multiplication. The cell process of multiplication forms a berry-like mass of cells called the morula. The process of forming the morula occurs over about four days as the cells travel along the fallopian tube towards the uterus. In the uterine cavity, the cluster of cells becomes hollow and fluid filled and is called a blastocyst (Yamauchi, Shaman, & Ward. 2011). At this point, the uterine wall is well thickened and vascularized ready for implantation of the fertilized ovum. The blastocyst burrows into the uterine wall and is covered by the uterine lining. Implantation takes place at day six and is completed by day seven after fertilization.

Embryology

During and after implantation the embryo develops a protective, fluid-filled capsule that surrounds and cushions the developing body to prevent injury. Two membranes enclose the embryo and the amniotic fluid, an inner amnion, and an outer chorion (Chamberlain, Manning, & Morrison, 2011). The root-like tufts, some of which form the early placenta, covers the chorion. The placenta is an organ made by the baby and the mother which transfers nutrients from the mother’s bloodstream and removes waste products from the child’s. The mother’s and baby’s circulatory systems are separate. The placenta secretes some hormones that maintain the pregnancy. The umbilical cord, the lifeline channeling nourishment in and taking wastes out, connects the baby to the placenta (Baschat & Weiner, 2000). The cord is cut close to the baby’s abdomen at birth and leaves the mark of the navel. During pregnancy, the baby obtains oxygen from the mother’s blood via cord and placenta. Fetal development in the womb occurs in three phases called trimesters.

First trimester

The first phase runs from weeks one to twelve. Week one through to four is the period when the fertilized ovum undergoes embryological changes. The implanted blastocyst undergoes rapid differentiation to form the different parts of the body. Between weeks three and four, the body plan emerges as rapid growth of the relatively flat embryo – particularly that of the central nervous system, causes a dramatic folding of the embryo. This folding forms the chest and abdominal cavities and incorporates a portion of the yolk sac which becomes the lining of the digestive and respiratory tracts. Thus, development of the digestive system is underway just four weeks after fertilization. The limb buds become visible by the fourth week. These buds are the first visible indication of the developing arms and legs (Robertson & Tickle, 2007). Specialized somites in the embryo’s back begin forming the dermis of the skin and the skeletal muscles, which the baby will use for voluntary movement. These somites will also form the bones of the spinal column, skull, sternum, and ribs. Skeletal muscles eventually enable you to move your body.

The heart and major blood vessels begin to develop earlier—by about day 16. The heart starts to pump fluid through blood vessels by day 20, and the first red blood cells appear the next day. Almost all organs are in complete form by about ten weeks after fertilization (which equals 12 weeks of pregnancy). The exception is the brain that continues to develop throughout pregnancy. Most malformations (birth defects) occur during the period when organs are forming which is in the first trimester. During this time, the embryo is most susceptible to the effects of drugs, radiation, and viruses.

Second trimester

The second phase runs from weeks 13 through to 27. During the second three months of pregnancy, the baby kicks, can hear and has a firm grip. The mother experiences quickening, this is the first movement of the baby that she feels. At 16 weeks, a steady heartbeat is apparent. The skin of the fetus is see-through, and the nails begin to form. The baby can roll over in the amniotic fluid. At 20 weeks, the heartbeat can be heard with a fetoscope (Mitra, Laurent, Moore, Blanchard Jr, & Chescheir, 2006). A protective coating covers the baby’s skin; the eyes are open and meconium, which will be his first bowel movement after birth, is collecting in his colon. The nervous system is beginning to function. The reproductive organs and genitalia are now well formed. By the end of the sixth month, your baby is about 12 inches long and weighs about 2 pounds. His or her skin is reddish in color, wrinkled, and veins are visible through the baby’s translucent skin. Baby’s finger and toe prints are visible. The child may respond to sounds by moving or increasing the pulse, and the mother may notice jerking motions if the baby hiccups.

Third trimester

This phase runs from week 28 to week 40. The baby’s size increases considerably. Lanugo, the fine downy hair, begins to disappear, first from the face whereas the vernix, the thick creamy-white substance, still protects the skin. The baby’s vision has developed, and his/her ears are now capable of picking up sound. If a light is shone directly on the mother’s abdomen, the baby will react to it. The baby can also hear the mother’s heartbeat, as well as food moving through her body and blood flowing through her uterus. The baby also is familiar with the mother’s tone. Loud music or sudden movements will cause the child to jerk, a startle reflex. The baby’s activities get better in strength. By sometime around week 32, the baby weighs approximately five pounds and is from 16 to 18 inches long. In this period, the fetus experiences tremendous development, especially the brain. Most of the baby’s systems are well developed by this point, except the lungs, which could still be underdeveloped. The baby is now plump and pink, smooth skin and mature enough for birth.

Birth

At term, hormonal changes stimulate muscular contractions of the uterine wall. Delivery has four key stages. The first two steps that lead to birth are dilatation of the cervix and expulsion of the fetus. Removal of the membranes and the placenta and recovery occur after birth (Jangsten, Mattsson, Lyckestam, & Hellström. 2011). The mother begins to labor and is due for delivery. The cervix gradually opens to allow the baby to pass through. The amnion tears and releases the amniotic fluid. Contractions become more frequent and intense as the child passes through the cervix and vagina. A skilled midwife then helps in removing the membranes and the placenta.