Parenting Excerpts
All About Conception
By Catharine Parker-Littler, author of Ask A Midwife
Reprinted with permission from DK Press.
All about conception; the beginning of life.
Conception occurs once an egg is successfully penetrated by one sperm. The journey of the egg and the sperm, although apparently simple, requires a whole complex chain of events to occur for fertilization to take place.
How is the egg released and fertilized?
After menstruation, the body secretes follicle-stimulating hormone (FSH), which acts on the ovaries to mature a follicle containing an egg. At the time of ovulation, a rise in the level of luteinizing hormone (LH) triggers the release from the ovary of an egg, which travels into the fallopian tube to await fertilization by a sperm. Up to 300 million sperm are released in each ejaculate, and of these only around 200 make it into the fallopian tube. These remaining sperm swarm all over the egg and many sperm bind to its surface. At this stage, the sperm then shed their bodies and tails and release enzymes to help them burrow down into the egg. However, only one sperm can penetrate the innermost part of the egg, known as the oocyte. Once the egg and sperm have successfully fused together, fertilization has taken place.
How are genes inherited?
The sperm and egg each contain 23 chromosomes that carry the genetic material of the parents. As human cells contain 46 chromosomes, once the egg and sperm fuse, their chromosomes join to provide the fertilized cell with a full complement of chromosomes. Each egg and sperm carries its own unique set of genes in the chromosomes, which means that the resulting baby has its own individual genetic makeup. The exception is identical twins: they result from one egg and sperm and inherit the same genetic code.
From conception to implantation:
The fertilized cell that results from the fusion of the egg and sperm is called a zygote, which divides into two identical cells and continues to divide as it begins its journey down the fallopian tube until it forms a bundle of around 100 cells, called a blastocyst. About a week after fertilization, the blastocyst embeds itself in the lining of the uterus, the endometrium. At this point the pregnancy is established: the blastocyst develops into an embryo and the placenta develops. The hormone human chorionic gonadotrophin (hCG) is released; this stimulates the production of progesterone, which maintains the lining of the uterus.
First signs of pregnancy:
The most obvious initial sign that you are pregnant is a missed period. Other common early pregnancy symptoms include feeling extremely tired and bloated, having increasingly tender breasts, experiencing an increased need to urinate, and finding that you have a greater or lesser sex drive, although all of these symptoms can occur premenstrually. Some women also experience spotting around the time their period was due, which may be confused with a lighter period that occurs when a fertilized egg implants in the wall of the uterus. There may also be a metallic taste in the mouth, nausea or vomiting – described as morning sickness, although this can occur at any time of day. Some women don’t experience any symptoms.
Pregnancy tests can determine if you are pregnant by detecting the hCG hormone in your urine….Most pregnancy tests can now detect hCG as early as the day you are due to have your period.
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