Couples wishing to use a natural method to avoid pregnancy need to learn to accurately identify the phases of fertility and infertility by observing and recording the indicators of fertility:

  • Basal body or waking temperature

  • Cervical mucus secretion

  • Changes in the Cervix

  • Cycle length

  • Minor indicators

More - Indicators of Fertility

It is assumed that anyone continuing to read this section,
is already familiar with The 'Indicators of Fertility'

A multiple indicator approach, generally a combination of temperature and mucus or sympto-thermal approach is the most effective method. When taught by an experienced teacher this will be up to 98% effective in avoiding pregnancy.

A teacher will recommend appropriate equipment including
Instruction is required in how to observe and record symptoms accurately. It is important to be aware of factors which may affect the cycle or disturb the recordings. These are summarised below:

Alcohol Holidays Stress
Late night Travel Illness
Disturbed night Time zones Gynaecological disorders
Oversleeping Shift work Medication

Some women will be more affected by common disturbances than others. With appropriate support most women will learn to define their limits of fertility while recognising the effects of disturbances on the cycle.

The book 'Fertility' includes a chapter on 'Factors affecting the menstrual cycle, which looks at the effects of stress, illness and medication on the cycle.

The guidelines for avoiding pregnancy are included here for information. It is strongly advisable to use these in consultation with an experienced NFP teacher. Please note these guidelines are only relevant for women of normal fertility.


Pre-ovulatory relatively infertile phase

The pre-ovulatory relatively infertile phase can be identified by the mucus symptom, cervical signs, a calendar calculation or the Doering rule.

It is advisable to have a double check and to consider the onset of the fertile phase as given by the earliest indicator.

Mucus symptom

Following the period, dry days are infertile.

It is wise to restrict intercourse to alternate evenings, because the presence of seminal fluid in the vagina may mask cervical mucus.

The day on which mucus is first recognised marks the end of this phase.

Cervical signs

Days on which the cervix is low, long, firm, closed and tilted are infertile.

The first day of change in position or texture marks the end of this phase.

Calendar calculation

Shortest cycle minus 20 = Last infertile day

The pre-ovulatory infertile phase lasts from the first day of the cycle until the last infertile day inclusive.

Doering rule

Earliest temperature shift minus 7 = First fertile day

The pre-ovulatory infertile phase lasts from the first day of the cycle up to, but not including the first fertile day.

The calendar calculation and the Doering rule should be based on information from at least six cycles.

Post-ovulatory infertile phase

The post-ovulatory infertile phase can be confirmed by the temperature, mucus or cervical signs :-


After the third high temperature has been recorded provided:

  • All three high temperatures are undisturbed

  • At least one is min. 0.2 deg C above the coverline

  • Minimum of six low temperatures
Mucus symptom

On the fourth evening after peak day

Cervical signs

On the third day after the cervix has returned to its infertile state

Using the sympto-thermal method

The post-ovulatory infertile phase starts:

  • after the third high temperature has been recorded
  • provided that all three high temperatures are past peak mucus day.

The figure below is included to show how natural methods can be used to avoid pregnancy by using a combination of indicators to increase the efficiency of the method.

For a systematic approach to interpreting a sympto-thermal chart see:

Sympto-thermal Chart Interpretation. in the Indicators of Fertility

Completed sympto-thermal chart showing correlation between all indicators of fertility.


  • The temperature shows two distinct levels - separated by a horizontal line or coverline. The temperature shifts to the higher level on day 17, confirming ovulation.
  • The period (shown in red) is followed by several dry days. A calculation to consider the effects of the shortest cycle has been made - this indicates that the fertile phase will start on day 9. Mucus changes are first noticed on day 10 and the cervix shows its first sign of change on day 12. Considering the earliest indicator as the first warning of approaching fertility, the fertile phase starts on day 9.
  • Peak mucus day is the last day when the mucus shows highly fertile characteristics - day 16 in this example. For the majority of women, peak day coincides closely with ovulation. The fertile phase is indicated in yellow.
  • The post-ovulatory infertile phase is confirmed following three high temperatures after peak mucus day - on day 19. The remainder of the cycle will be infertile - shown in green. This phase extends until the next period.

  Effectiveness of the pre-ovulatory relatively infertile phase

Intercourse in the pre-ovulatory infertile phase always carries a slight risk of pregnancy. It is in this phase we consider male fertility, because in the presence of early mucus, the life of the sperm may be prolonged.

Ovulation could occur earlier than anticipated. In a very small number of women, with short cycles of around 21-24 days, or with prolonged menstrual bleeding, mucus may appear immediately after the period or even before its end. In this case intercourse during a period could lead to conception. There will be no pre-ovulatory relatively infertile phase.

Effectiveness of the post-ovulatory infertile phase

It should be emphasised that the post-ovulatory infertile phase is the safest time for intercourse for a couple wishing to avoid pregnancy. When ovulation has been confirmed there is no risk of further fertility in the current cycle.

The above sympto-thermal chart shows a normal fertile pattern. There will however be various times throughout reproductive life when fertility may be affected.

  Special circumstances
After stopping the contraceptive pill

Most women will return to normal fertility very quickly. In fact the chances of getting pregnant immediately after stopping the pill are higher than normal. Women who stop the pill and want to use a natural method, need to be aware that it may take up to several months to be able to accurately define the phases of fertility and infertility, due to the effects of the synthetic hormones. Help will be required from an experienced NFP teacher to use a natural method after stopping the pill.

A chapter for post-pill users including a series of charts is included in the book 'Fertlity'.

During breast-feeding
It is possible to record fertility indicators during breast-feeding and to rely on a natural method watching for the return of fertility as breast-feeding is reduced. As there may be weeks or months of infertility associated with breast-feeding, many women now rely on Lactational Amenorrhoea Method or LAM and start recording fertility symptoms again (or choose another family planning method), when indicated by this method.

A section on Fertlity Awareness and NFP post-natally and during breast-feeding is included in the book and video 'Fertliity'.

More - Breast Feeding.

  During the pre-menopausal years

If a woman has previous experience of Fertility Awareness during normal fertile cycles this can be very helpful in identifying early changes related to the pre-menopause.. It is possible to start using natural family planning at this time despite cyclic irregularities, provided a woman has the support of an experienced NFP teacher. Women who have used natural methods successfully for a number of years will need further help to interpret their charts as cycles become irregular.

A chapter in ‘Fertility‘ gives further details. See Books - ‘Fertility‘

Barrier users and fertility awareness

It is true that barrier methods do not need to be used on every day of the cycle. A knowledge of fertility awareness can help couples to identify the days when they are fertile, thus reducing the use of barriers to a minimum while ensuring an effective means of avoiding pregnancy. There are special considerations, however. The use of spermicides during the pre-ovulatory phase can make the recognition of the mucus symptom difficult. Some women rely more heavily on changes in the cervix. It is important that couples understand the failure rate associated with barrier use. This will vary dependent on the chosen barrier - male or female condom or diaphragm and spermicide. (see table below) As women recognise their limits of fertility and time of maximum fertility, many will choose to avoid intercourse completely during the days of peak fertility.


When considering the effectiveness of any form of family planning, the distinction must be made between:-

  • the theoretical or method effectiveness - the biological effectiveness
  • the practical or use effectiveness - the behavioural effectiveness.
The theoretical or method effectiveness is the maximum effectiveness of the method when used without error or omission, that is when used according to the instructions. In theory the effectiveness rate for the sympto-thermal method, for example is around 98 per cent.

  The practical or use effectiveness takes into consideration all users of the method, that is those who follow the method without error and also those who are less committed and less consistent in their use. It denotes the effectiveness under real life conditions - for example the sympto-thermal method has an effectiveness rate of 85-98 per cent.

Use effectiveness of family planning methods is expressed as a percentage per 100 women per year.


User effectiveness of family planning
· Combined pill 97% - 99%+
· Progestogen only pill 96% - 99%
· Injectables and implants 98% - 99%+
· Intra-uterine system (IUS) 99%
· Intra-uterine device (IUD) 98% - 99%+
· Diaphragm or cap with spermicide 82% - 96%
· Condom 85% - 98%
· NFP - Sympto-thermal method 85% - 98%
Source - Family Planning Association 1995

A couple‘s motivation has a crucial influence on the use effectiveness of a number of methods of family planning. The first year‘s use always carries the highest risk of unplanned pregnancy due to the time taken for a couple to learn to use the method efficiently.

Barrier methods require some skill and a high degree of motivation and pills are more frequently forgotten during the first year of use.

  Effectiveness of natural family planning

A high degree of motivation is essential if a couple are to use natural methods of family planning successfully. They should both be in accord about their goals of family spacing or limiting. It is interesting to note that the family-spacers, those who plan more children but at a later date, are less effective in preventing pregnancy. They are prepared to take risks; whereas family limiters, those who have completed their family, are more conscientious and determined, and more successful in preventing pregnancy. This is illustrated by a 1976 Canadian sympto-thermal study which showed an effectiveness rate of 85 per cent for the family spacers but around 99 per cent for those limiting their families. (Parrenteau-Carreau, Lanctot and Rice)

The effectiveness of any form of family planning depends on the method being well taught, well understood and well applied, but this is of particular importance for natural family planning. With experience, the sympto-thermal method is a highly effective method.

Efficiency studies of Sympto-Thermal method

Advances in teaching techniques and use of multiple index methods have considerably reduced the unplanned pregnancy rate among NFP Users. The method is however unforgiving of imperfect use.

The frequently quoted 80% efficiency dates back to a WHO trial using cervical mucus as a single indicator. (WHO - A prospective trial of the ovulation method of NFP - II The effectiveness phase. Fertility and Sterility 1981, 36; 152-8.)

The most recent study of the sympto-thermal method reported a use effectiveness rate of 97.7% (Frank-Hermann, Freundl et al, Effectiveness and acceptability of the sympto-thermal method of NFP in Germany, American Journal of Obstetrics and Gynecology, 1991, 165,pp 2052-4)

Home Kits and devices to predict fertility


PERSONA is a new personal contraceptive system launched on September 30th 1996. The system consists of a small hand-held computerised monitor and disposable urine test sticks. After extensive research, European trials have shown PERSONA to be 94% effective.

PERSONA uses the same principles as NFP, but measures hormones directly rather than the effects of the hormones on fertility indicators. The test stick identifies the start of the fertile phase by a rise in oestrogen and the end of the fertile phase by measuring the LH surge and then allowing time for ovulation and ovum survival.

The monitor displays:

  • A Yellow light when a test is needed

  • A Green light for infertile

  • A Red light for fertile

  • The monitor requires 8 tests per cycle and typically identifies 6-12 ‘red’ days.


  • identifies the days in each cycle when you are at risk of becoming pregnant

  • is free from side effects

  • is 94% reliable when used according to instructions.

  • is easy to use and requires only eight urine tests each monthly cycle (16 during the first cycle)

  • learns about your individual cycle - and so becomes completely personal to you.

PERSONA is currently available from Boots and leading chemists in the UK.

The monitor plus the first month's test sticks costs £64.95 and subsequent sticks cost £9.95 per cycle.

Further information is available from the Persona line on: + 44 (0845) 608 6081

Alternatively you can access information on the World-wide Web on: www.persona.org.uk

PERSONA is not suitable :
  • for women with irregular cycles (outside the range of 23-35 days),

  • for 2 cycles after stopping the pill,

  • during breast-feeding or during the pre-menopause.

Reference Bonnar J, Flynn A, Freundl G, Kirkman R, Royston R, Snowden R, (1999)
Personal hormone monitoring for contraception, British Journal of Family Planning, 24, 128-134

Full details of using NFP to avoid pregnancy, including illustrations of normal and abnormal charts
are included in the book and video 'Fertility'.

These resources should be used with the support of a trained NFP teacher.

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Information contained here is for interest only.
To use this method effectively - a full course of instruction by a recognised NFP teacher is vital!

‘FertilityUK‘ - The National Fertility Awareness and Natural Family Planning Service UK,