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Fertilization marks entry of spermatozoids into the ovary unit, When the spermatozoid fertilizes the ovary unit, it has 46 chromosomes (23 from spermatozoids and 23 from the ovum). This is the most important event in the reproduction process.
The chromosomes bear genetic data for the development of a new organism, including the sex of the child. The ovary unit contains the X-chromosome, while the spermatozoid contains X or Y chromosome. If the ovary unit is fertilized by a Y-chromosome spermatozoid, the baby boy will be born (XY), and in case it is fertilized by a X-chromosome spermatozoid, a baby girl will be born (XX).
The fertilization (2) takes place in the fallopian tube, while the fertilized ovary unit is an embryo. Parallel with the separation, the journey begins through the fallopian tube toward the uterus for the next three to four days. The picture on the right shows the separation of the fertilized ovary unit 54 hours after fertilization as an eight-unit embryo.
The fertilized ovary unit is first separated in to two (3-5), then in four units (6) that are called blastocysts, and separates further until it forms a round form made of units (7). When the fertilized ovary unit enters the uterus, over the next three days it floats inside and then settles on the inner wall (9-10). This is an implantation, by which the fertilization process is completed. The membrane of the uterus is thickens under the influence of hormones with an increased number of blood vessels and this way it is prepared for accepting the ovary unit.
The role of maintaining the pregnancy is gradually taken by the placenta, which the embryo and enables its growth. Womb liquid inside the amnion bubble around the fetus enables comfortable conditions protecting it from injuries. By an optical instrument inserted in the uterus, the picture of the fetus can be made.
The placenta keeps the connection between the mother and the fetus, feeding it and removing waste substances, and is linked with the child through the umbilical cord.
Eight week after the fertilization, important organs are developed, both the face and limbs, and the embryo is transformed into a fetus. The heartbeats can be heard, and with ultrasound the fetus can be seen at the earliest stage of pregnancy. The picture shows a 12-week old fetus using 3D ultrasound.
Between the 18th and the 20th week of pregnancy the woman will feel the child’s movement. Its length is about 20 cm (A). During the 24th week (B), the child’s length is about 30 cm, and in the 32nd week (C) it is about 40 cm. Pregnancy lasts 40 weeks or 280 days. After 40 weeks, a child is born in most cases with its head going out (d), and rarely with legs (e). Absence of menstruation is usually the first and most reliable sign of pregnancy. Other signs might be: sensitivity of breasts, more frequent urination, tiredness, desire for specific food or dislike of certain food, feeling nauseous in the morning, white secretion from the vagina and other.
The pregnancy test should be made in a medical institution. The presence of hormones in urine is tested. The test can be fake positive or fake negative and therefore a gynecologist checkup is necessary.
With the ultrasound it is possible to monitor the growth and the development of the fetus and the possible anomalies. It is important that the woman during pregnancy takes care of herself, with a proper diet and often rest and not to take medicine and harmful substances – tobacco, alcohol and drugs. Smoking and alcohol during pregnancy often causes difficulties in growing of the fetus, which can result in giving birth to children of low delivery weight and with increased health and life risks.
During pregnancy, some difficulties may occur, such as high blood pressure, trapped liquid inside the organism and kidney dysfunction, which are a threat for both the mother and the child. Therefore the medical checkups during pregnancy are extremely important. The picture on the right shows the 12-week old fetus with 3D ultrasound.
Ectopic pregnancy is development of a fertile ovum outside the uterus, usually inside the ovary duct. The reason is an impassable ovary duct which is under inflammation (most often as the consequence of sexually transmit diseases) and cannot let the ovum into the uterus. This can be lethal for the woman because of massive internal bleeding and the state of shock. A woman with these symptoms of very intensive and sudden pain in the lower part of the stomach (but not during a menstrual period) must urgently be taken into the hospital for an operation.
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Pregnancy 
