The fertility of the couple is a shared fertility.The man is always fertile from puberty onwards for the rest of his life,1 the woman is fertile for just some days in the menstrual cycle, this means the woman’s fertility is cyclical.
What are the reproductive cells?
The reproductive cell is known as the gamete. The male gamete is the sperm, and is produced by the male gonad, the testis.
The female gamete is the ovum (egg) and is produced by the female gonad, the ovary. The gamete differs from other cells in the body as its nucleus contains just 23 chromosomes, while all other cell nuclei contain 46 chromosomes. The chromosomes carry DNA, the genetic material unique to each individual.
What does ‘fertilisation’ mean?
Fertilization is when the nucleus of the sperm and the nucleus of the ovum fuse together2, and this is the beginning of a new human individual who has a full DNA complement of 46 chromosomes unique to him/her alone, having received half the genetic material from the mother and half from the father. Fertilisation occurs at the outer end of the fallopian tube. (see Fig. 6-16, ‘Factors necessary to achieve pregnancy’ under the heading ‘Achieving Pregnancy’).
Why are the child-bearing years of the woman limited?
The testis continues to produce sperm throughout the adult life of the man, but the woman will make no new ova after birth.3 This means that every girl when she is born already has the finite number of oocytes,(called primordial follicles, immature eggs), to last her child-bearing years. A steady loss of oocytes from the ovary is occurring throughout the child-bearing years due to atresia or ovulation.6 In fact even though the oocyte pool is depleted when the woman has reached ‘menopause’, only about 500 ovulations have occurred over the child-bearing years.6
What is the Graafian Follicle?
During the first phase (follicular phase) of each menstrual cycle a small number of these oocytes (immature eggs or follicles) in the ovary start to mature under stimulation by follicle stimulating hormone (FSH) from the pituitary gland, and one follicle (sometimes two follicles) continues to grow and becomes dominant. The dominant mature follicle is called the Graafian follicle and consists of the mature ovum (egg) surrounded by follicular fluid. During the follicular phase the oocyte (immature egg) increases in size from 15micron to 135micron* when it is the mature ovum, to become one of the largest cells in the body as it has to sustain the pregnancy until implantation occurs.5 (* 1 micron = 0.001mm = one thousandth of a millimetre).
What is ovulation?
Ovulation is the release of the mature ovum into the outer end of the fallopian tube ready to be fertilised by the sperm. The egg is released from the mature follicle (Graafian follicle) which ruptures when it has reached its maximum size, (about 2.3cms due to the increase in follicular fluid). This event is called ovulation and is triggered by the luteinizing hormone (LH surge) from the pituitary gland. The ovum lives for 24 hours after it is released and it is fertilizable for only 12 – 16 hours during those 24 hours. Fertilisation takes place in the outer end of the fallopian tube.
What does ‘implantation’ mean?
‘Implantation’ refers to the embedding of the embryo in the lining of the uterus (endometrium). After fertilisation the fertilised ovum, now called the embryo, travels down the fallopian tube to the uterus and implantation occurs about seven days later in the endometrial lining of the uterus.4 (see Fig. 6-17, ‘Factors necessary to achieve pregnancy’ under the heading ‘Achieving Pregnancy’).
The child-bearing years last about 35-40 years and the last menstrual cycle occurs when the quota of ova have been exhausted. This marks the arrival of the menopause.
- Odeblad Erik; ‘The discovery of different types of cervical mucus and the Billings Ovulation Method'; Bulletin of the Ovulation Method Research and Reference Centre of Australia, Vol 21, No3; 3-35; Sept 1994. (on the internet if you google ‘Erik Odeblad, cervical mucus’)
- Flynn, Anna & Brooks Melissa; ‘The Manual of Natural Family Planning’ p32; 1996; ISBN 0 7225 3115 X
- Lamb JF, Ingram CG, Johnson IA, Pitman RM; ‘Essentials of Physiology’ 3rd Edition, page 252;Blackwell Scientific Publications 1991, ISBN-632-03135-2
- Griffin JE, Ojeda SR; ‘Textbook of Endocrine Physiology 3rd Edition,1996, page 226; Oxford University Press, ISBN 0-19-510755-1 (pbk)
- Manassiev Nikolai, Whitehead, Malcolm; ‘Female Reproductive Health'; p7; 2004; ISBN 1-85070-491-0
- Soules MR, Sherman S, Parrot E et al; Executive Summary: Stages of Reproductive Aging Workshop (STRAW). Fertil Steril; 2001;76;874