<ul><li>Every normal human cell contains 46 chromosomes (23 pairs). The ovum however, has at some stage split, and therefore only contains half the chromosomes of other cells in the human body. </li></ul>
<ul><li>Similarly each human sperm only has 23 chromosomes. </li></ul>
Fertilization, also called conception, occurs when a single sperm enters the ovum (egg) and their nuclei fuse. The two nuclei combine together to form a full 46 chromosome cell.
Thus, the resulting newborn will contain a DNA that has been derived from a combination of its mother and father.
Fertilisation This usually occurs in the upper part of one the Fallopian Tubes.
A photo of a human ovum (egg) magnified many times
The average pregnancy lasts for 38 weeks from the date of conception. However, doctors usually date your pregnancy from the first day of the woman’s last menstrual period — that is the day the last period started . Using this method a pregnancy is said to last 40 weeks Dating the Pregnancy
Within 38 hours, cell division begins. Firstly into two then four etc….
The fertilised egg, now a number of cells, makes its way to the uterus, so by the 10 th day, it embeds itself in the protective walls of the uterus
12 days or so after conception the fertilised egg or blastocyst as it is now known has started to produce hormones which can be detected in the woman's urine.
3 weeks after conception (week 5) the embryo is the size of a grain of rice (about 2 mm long) and would be visible to the naked eye. It has the beginnings of a brain with 2 lobes and its spinal cord is starting to form.
At 6 weeks of ‘pregnancy’ (3-4 weeks after conception) the embryo has a head with simple eyes and ears. Its heart has 2 chambers and is beating. Small buds are present that will form arms and legs later.
What is known as the embryonic period finishes at the end of week 8 (week 6 since conception) and the fetal period begins. This period sees rapid growth of the fetus, and the further development of the organs and tissues that were formed in the embryonic period.
By week 12, its body is fully formed, including ears, toes and fingers complete with fingernails. The external genitals appeared in week 9, and now, by week 12, have fully differentiated into male or female genitals. The eyes have moved to the front of the face and the eyelids remain closed together.
By 14 weeks the baby will be about 9-10 cm long. It may suck its thumb now. Its body is now covered with a layer of fine hair called lanugo. By 16 weeks its face is becoming more human in appearance
By 24 weeks your baby’s organs are fully formed. The baby now has the face of a newborn baby, although the eyes are rather prominent because fat pads are yet to build up in the baby’s cheeks. The eyelids are fused until weeks 25 to 26 when they open.
The baby is becoming plumper. By 30 weeks the toenails are present and by 32 weeks the fingernails have developed. The eyes will be open when the baby is awake. By about 32 weeks the baby will have settled into a downward position as there is no longer enough room left in the womb for it to move about freely. Baby now facing down and engaged into birth position