Fig. 6-16; Ovulation-fertilisation: The more-fertile mucus transports sperm from the cervical os to the uterus and both fallopian tubes. The ovum has been released from the ruptured Graafian follicle in the ovary (i.e. ovulation has occurred), and one sperm has reached the outer end of the left fallopian tube and is about to fuse with the ovum (fertilization). In the ovary, the granulosa cells in the wall of the Graafian follicle become the corpus luteum which secretes progesterone to support the pregnancy until the placenta takes over this function at about 8 weeks gestation.4 (see Fig.6-17)
Factors necessary to achieve pregnancy (Fig. 6-16, Fig. 6-17)
- A healthy mature ovum.
- A healthy mature sperm.
- A healthy patent fallopian tube through which sperm travels to fertilize the ovum and the fertilized ovum travels to the uterus.
- An endometrium that has been prepared to accept a fertilized ovum first by the action of oestrogen before ovulation, and then by the action of progesterone after ovulation.
- A healthy corpus luteum for the secretion of adequate levels of progesterone to maintain the pregnancy in the uterus until the placenta takes over this function at 8 weeks gestation.4
- Cervical Mucus : Pregnancy cannot occur without the presence of more-fertile cervical mucus as the function of this type of mucus (L mucus, S mucus) is to transport sperm, to nourish sperm and to filter sperm.1
- A healthy life style that is well balanced between work and leisure with a well balanced diet.2
Transport of the fertilized ovum to the uterus – implantation
Fig. 6-17; Transport of fertilised ovum to the uterus-implantation: The ovum is fertilised in the outer end (the ampulla) of the fallopian tube; the fertilized ovum is called a zygote. Once the zygote begins to divide it is called an embryo. The embryo starts to divide rapidly during its passage through the fallopian tube and on Days 3-4 enters the uterine cavity at the 8-16 cell stage (morula); the morula is transformed to a blastocyst during the 5th to 6th day after fertilisation when the embryo is at the 16-32 cell stage. On the seventh day after ovulation, the blastocyct implants on the endometrial lining of the uterine cavity.4 The implanting blastocyst starts secreting human chorionic gonadotrophic hormone (hCG) which prevents the demise of the corpus luteum.3 Progesterone from the corpus luteum supports the pregnancy for 8 weeks after conception after which the embryo is capable of synthesizing all steroid hormones required for its development.3,4 (Fig. 6-17 from the Fertility Education Trust UK, 2003, is used with the kind permission of Colleen Norman).
- Erik Odeblad; ‘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’).
- Klaus, Hanna; ‘Natural family planning – Is it scientific? Is it effective?’ see pages 13,14; Newman Lecture Series 1 -May 21, 2000. ( this is available on the internet if you google ‘natural family planning, Dr Hanna Klaus’).
- Manassiev Nikolai, Whitehead, Malcolm; ‘Female Reproductive Health’; 2004, ISBN 1-85070-491-0
- Griffin James E, Ojeda, Sergio R; ‘Textbook of Endocrine Physiology’ ;1996, p226-228; ISBN 0-19-510755-1(pbk)