Fertility awareness means that the woman, by self-observation of the various signs and symptoms recurring during the menstrual cycle, can identify the fertile and infertile phases of the cycle herself, irrespective of cycle length.4 These signs and symptoms have a physiologic and scientific basis 6 and are due to the effects of the varying levels of the ovarian hormones oestrogen and progesterone on the fertility indicators during the cycle. The most important fertility indicators are ‘cervical mucus’, ‘basal body temperature (BBT)’ and ‘cervix’.
Can fertility awareness and natural family planning be used by women with irregular cycles ?:
All women can use fertility awareness and natural family planning to identify when they are potentially fertile by learning to recognise the changes in the fertility indicators, that is, changes in the ‘cervical mucus’, ‘basal body temperature’, and ‘cervix’ during the cycle, (fertility awareness). This applies to all women of child-bearing age whether their menstrual cycle is regular or irregular.
The fertility indicators are :
- change in basal body temperature, (thermal shift).3
- changes in quality and quantity of cervical mucus.4
- changes in the cervix itself.5
The woman may also find other fertility indicators of a minor nature useful, such as the ‘calendar calculation’, and the presence of various symptoms (called molimina) e.g. ‘ovulation pain (mittelschmertz)’ or ‘breast symptoms’.
When is the fertile phase of the menstrual cycle and how long does it last? : The fertile phase of the cycle includes the time when the mature ovum is available for fertilization at ovulation and the 6 days or so leading up to ovulation when oestrogenic fertile-type cervical mucus is present. The fertile phase is the combined time of the lifespan of the ovum (egg) after ovulation, (24 hours), and the lifespan of sperm in fertile-type mucus before ovulation, (5 days).1,2 Therefore the fertile phase during which sexual intercourse could potentially result in conception lasts for 6 – 9 days.7
- Wilcox AJ, Weinberg CR, Baird DD; ‘Timing of sexual intercourse in relation to ovulation – effects on the probability of conception, survival of the pregnancy, and sex of the baby'; N Engl J Med 1995; 333;1517-21.
- Simpson JL; Editorial, Pregnancy and the timing of Intercourse; N Engl J Med 1995; 333;1563-64.
- Marshall, J; A field trial of the basal body temperature method of regulating births; Lancet,1968,July, 8-10;
- Billings, E & J; Symptoms & Hormonal Changes accompanying ovulation; Lancet; Feb5; 1972; 282-284.
- Keefe, E.; ‘Self-observation of the cervix to distinguish days of possible fertility'; Bull of the Sloane Hosp for Women; 1962; 129-136.
- Moghissi KS, Syner FN, Evans TN: ‘A composite picture of the menstrual cycle'; Am J Obstet Gynecol, 1972; 114:405- 418.
- Freundl G, Godehardt E, Kern PA, et al; “Estimated maximum failure rates of cycle monitors using daily conception probabilities in the menstrual cycle”; Human Reproduction, (2003), vol 18, no. 12, p2628-2633.
How can the woman identify the fertile phase of the cycle?
By becoming familiar with the changes in her body associated with the fertile and infertile phases of the menstrual cycle, (fertility awareness), the woman will be able to identify when the fertile and the infertile phases of the cycle begin and end. These signs in her body which the woman can detect herself are called the fertility indicators, (changes in the cervical mucus and in basal body temperature, BBT), and are due to the effects of the ovarian steroid hormones oestrogen and progesterone.
The fertility indicators are classified as major indicators which can detect either the beginning or end of the fertile phase, and minor indicators which are inconstant and do not detect the beginning or the end of the fertile phase.2 The scientific basis for these effects are well described in the study by Moghissi.1
An example of a minor index is ovulation pain (mittleschmerz), or the ‘calendar calculation’.
- Moghissi KS, Syner FN, Evans TN: ‘A composite picture of the menstrual cycle'; Am J Obstet Gynecol, 1972; 114:405- 418. Commenting on this study by Moghissi, Dr M.L. Taymor, Boston, Massachusetts states on page 416, “The special contribution of this paper is the correlation of the changes in the end-organ responses, i.e. BBT, and changes in cervical mucus, with the hormonal changes. As a result, these changes which are naturally of more interest to the clinician, are placed on a firmer physiologic basis.”
- Flynn A, Brooks M; ‘The Manual of Natural Family Planning'; 1996; ISBN 0 7225 3115 X