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Efficacy of Natural Family Planning Methods

There are two types of efficacy results that are reported with methods of family planning when used to avoid pregnancy.  The first type is the efficacy when the method of family planning is used consistently and according to instructions.  This type of efficacy is referred to as "perfect use" or "correct use" efficacy.  The second type of efficacy is when the method is not always used consistently and according to instructions.  This type of efficacy is called "typical use" effectiveness.  It is the type of effectiveness that you will find when a method is used by a general population.  Efficacy results are reported as the percentage of unintended pregnancies that are experienced by 100 women over 12 months of use.    

There have been several published efficacy studies of the Marquette Method of natural family planning.  All of the studies involve the use of the ClearBlue fertility monitor along with cervical mucus monitoring.  In general, the perfect use efficacy of the Marquette Method ranges from 1-2 unintended pregnancies per 100 women over 12 months of use, in other words 98-99% effective to avoid pregnancy when used correctly. The typical use efficacy for the Marquette Method ranges from 10-12 unintended pregnancies per 100 over 12 months of use, or in other words, 88-90% effective to avoid pregnancy when not always used correctly.

In comparison, the hormonal birth control pill is over 99% effective when used correctly and about 92% with typical use (see comparison figures below).  Users of the Marquette Method need to realize that when they have intercourse during the fertile time they most likely will become pregnant. 

Pregnancy rate over one year by family planning method*

                                                           Correct Use   Typical Use

Chance 85 85
Spermicides 18 29
Withdrawal 4 27
Ovulation Method 3 19 (25)
Condoms 2 15
SDM 5 12
Marquette Method 0.6-2 11-12
Symptothermal 0.4-2 8 -11
Pill 0.3 8
IUD 0.1 0.6

 

*Adapted from: Trussell J.  
Contraceptive failure in the United States.  
Contraception.  2004;70:89-96.