Natural Family Planning (Fertility
Awareness) Reviewed by Dr Philip Owen, consultant obstetrician
What is fertility awareness?
This form of natural family planning
helps identify the phases of a woman's menstrual
cycle when she is most fertile as well as those
phases when she is less fertile and, therefore,
less likely to fall pregnant.
How reliable is natural family
It is not reliable as a form
of contraception when used on its own, but
it can be helpful both for couples wishing
to avoid pregnancy and for those actively trying
to have a baby.
If a woman's cycle is irregular
then natural family planning will be less reliable.
You should also bear in mind
that none of the methods that come under the
heading of natural family planning will protect
you from sexually transmitted diseases.
How does natural family planning
Natural family planning is based
upon certain facts about a woman's eggs and
a man's sperm:
a woman usually ovulates 14 days before
her next period.
for example, if a woman has a regular
28 day menstrual cycle, counting
the first day of her period as day
one, then she will usually ovulate
on day 14. If her cycle lasts 32
days, then she usually ovulates on
once ovulation has occurred, the sperm
has only 24 hours within which to
fertilize the egg in the woman's
sperm can survive for up to seven
days following intercourse.
With this knowledge it now becomes possible
to identify three phases of fertility during
each menstrual cycle. However, if a woman's
cycle is irregular then clearly it is more
difficult to predict when ovulation is likely.
The first phase is the first
infertile phase, or the first safe period when
the woman is unlikely to fall pregnant. This
starts on the first day of the woman's period
and ends on the earliest date from which sperm
could survive long enough to fertilize the
egg. This first safe period is short because
sperm can survive for up to seven days after
intercourse and a woman may ovulate early.
Therefore, unprotected intercourse during this
first phase may result in pregnancy.
The fertile phase is the time
when a woman is most likely to fall pregnant.
Couples not wishing to become pregnant, should
avoid intercourse during this time or use other
methods of contraception such as condoms. If
pregnancy is desired then this is the time
when a woman is most likely to conceive. The
fertile phase lasts from the end of the first
phase until 24 hours after ovulation.
The second infertile phase or
safe period when a woman is less likely to
fall pregnant is more predictable than the
first phase. This phase lasts from the end
of the fertile phase until the beginning of
the woman's next period.
Accurately identifying the time
of ovulation is the cornerstone of natural
family planning. The three principal methods
of calculating when ovulation is likely to
the calendar method
the temperature method
the mucus test
The calendar method
What is the calendar method?
The calendar method makes use
of our knowledge of when a woman is likely
to ovulate. This enables many women to calculate
their fertile and infertile phases described
above. The fertile period is 12-16 days before
the period starts.
How do I prepare for using the calendar
Before using the calendar method,
a woman has to make a detailed note of her
periods for six months. Each month, you should
note the number of days between starting one
period and the next. Then work out the longest
and the shortest interval between your periods.
Now you are ready to start calculating.
It can be hard to do it correctly
and you will need a pen and paper. From the
shortest interval you always subtract 18 days.
If for example, the shortest time between starting
one period and the next during the last six
months was 27 days, by subtracting 18, you
arrive at the 9th day after the start of your
From the longest interval you
always subtract 11 days. For instance if the
longest space between starting periods was
31 days, subtract 11 to arrive at the 20th
day after the start of your period. Using the
figures in this example, the first safe phase
would be from day one to day eight, the phase
when conception is most likely to occur would
be between day 9 and day 20 and the second
safe phase would be from day 21 to the start
of your next period. Please note that these
figures are an example only and you will need
to do your own calculations to work out your
own fertile and less fertile phases.
If your periods are more irregular,
the unsafe (fertile) periods will be longer.
What demands does the calendar method make?
This method of calculating ovulation
demands an accurate recording of your period
intervals. If you do not wish to become pregnant
you will need to be able to tolerate long periods
without sex unless other forms of contraception
are used. Alternatively, if a couple are trying
to have a baby, it can help them identify the
dates when conception is most likely to occur.
The temperature method (also
known as the basal body temperature or BBT
What is the temperature method?
As we have described above, the
chance of falling pregnant is much greater
around the time of ovulation. The temperature
method helps women find out when they are ovulating
by taking their temperature every morning.
The day after ovulation takes place a woman's
temperature will go up by about half a degree
Celsius under the influence of the female hormone
How to use the temperature method
Measure your so-called 'base'
temperature every morning after waking from
at least five hours of undisturbed rest, and
before getting out of bed. It is important
that your temperature is measured correctly
using the same, accurate thermometer every
day. If possible, it should also be taken at
approximately the same time every day. Keep
a record of your daily temperature. As soon
as three successively higher-than-average temperatures
have been noted (based on six previous measurements
that month), ovulation has taken place. This
is called the 'three over six rule'.
How long does this fertile period last?
From the third day after ovulation
- the third day of increased temperature -
it is almost certain that the egg will not
be fertilised and that the woman's body has
entered the second infertile phase.
What are the drawbacks or limitatations
of the temperature method?
Considerable motivation is required
to measure and record the temperature in the
correct manner each morning. This technique
cannot be used to identify the first infertile
phase, ie before ovulation. The temperature
recordings may become confused if the woman
has an infection such as a cold.
The mucous test
How does the mucous test work?
Over the course of every month,
the mucus produced by a woman's vagina and
cervix changes its characteristics because
of the fluctuating levels of the female hormones
oestrogen and progesterone. This will show
how close or far from ovulation she is.
A few days before ovulation (when
the egg is released) the mucus becomes transparent,
watery and yellowish. On the day of ovulation
itself, what comes out is thicker, wet and
thread-like (like egg-white) and might also
produce a moist feeling in the vagina. Within
a day of ovulation there is less mucus and
it is thicker and sticky.
How is the mucous test carried out?
Although the test is simple,
it is important to practice and to record the
findings in a diary.
Every morning (or every time
you use the toilet) check to see what is coming
out of your vagina and remove a little with
your fingertip. To work out whether the secretion
is at the stringy, ovulation stage mentioned
above, press the sample against your thumb,
then carefully separate your fingers. If the
mucus draws itself out into a long 'thread'
before breaking, you are probably ovulating.
The second infertile phase starts four days
after the day of peak mucus production (ovulation).
What are the drawbacks or limitations of
the mucous test?
It becomes difficult to assess
the nature of the mucus if you have recently
had intercourse. This is because the presence
of semen will make the mucus appear different
and sexual arousal in a woman also makes the
mucus more stringy.
The mucous test isn't a guaranteed
form of family planning, so don't rely on it
as a way to avoid getting pregnant. However,
it is good to combine the test with other forms
of contraception, eg condoms or diaphragms
and, in cases where contraception isn't available,
certainly better than nothing at all. If you
wish to become pregnant then identifying when
you ovulate will help you to identify your
Where can I find out more
about natural family planning techniques?
It is possible to obtain instruction
and advice in the use of natural family planning
techniques (fertility awareness) from appropriately
trained doctors and specialist family planning
nurses. This is strongly recommended if a woman
wishes to reduce her chances of falling pregnant
and also gives her the opportunity to discuss
alternative methods of contraception.
The opposite is also true; if
a woman is having difficulty conceiving then
awareness of when she is ovulating will enable
her to maximise her chances of falling pregnant.
Based on a text by Dr Erik Fangel Poulsen,