Fertility awareness methodsnatural family planning

Few couples in the UK use so-called natural methods of family planning (NFP) although in some parts of the world these methods are common. All involve the avoidance of intercourse during the fertile period of the cycle (periodic abstinence). Methods differ in the way in which they recognize the fertile period. The simplest is the calendar or rhythm method in which the woman calculates the fertile period according to the length of her normal menstrual cycle. The first day of the fertile period is calculated as being the length of the woman's shortest cycle minus 20 days, and the last day of the fertile period is the longest cycle minus 11 days. If therefore cycle length varies from 25-31 days the potential fertile period and days when intercourse should be avoided are days 5-20.

Other approaches use symptoms which reflect fluctuating concentrations of circulating oestrogen and progesterone. The mucus or Billings method relies on identifying changes in the quantity and quality of cervical and vaginal mucus. As circulating oestrogens increase with follicle growth the mucus becomes clear and stretchy allowing the passage of sperm. With ovulation, and in the presence of progesterone, mucus becomes opaque, sticky and much less stretchy or disappears altogether. Intercourse must stop when fertile-type mucus is identified and can start again when infertile-type mucus is recognized. Progesterone secretion is also associated with a rise in basal body temperature (BBT) of about 0.5°C. The BBT method is thus able to identify the end of the fertile period. Other signs/symptoms such as ovulation pain, position of cervix and degree of dilatation of the cervical os can be used additionally to help define the fertile period.

Whatever method is used, many couples find it difficult always to abstain from intercourse during the fertile period. Failure rates are high (Table 32.2) and most of the failures are due to conscious rule breaking. Perfect use of the mucus method is associated with a failure rate of only 3.4%. In a study of the mucus method couples who had completed their families had lower failure rates than couples who were using NFP as a method of birth spacing.

There is no evidence that pregnancies conceived with ageing gametes (i.e. towards the end of the fertile period) are associated with a higher risk of congenital malformations.

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