Transcript EMERGENCY CONTRACEPTION:

WHY CONTRACEPTION FAILS
James Trussell
Office of Population Research
Princeton University
Unintended Pregnancy
Unintended Pregnancies Defined
• Unintended pregnancies are defined as the
sum of mistimed and unwanted pregnancies
– Mistimed: a woman would have wanted children
later but not now
– Unwanted: a woman would have never wanted
(more) children
• Most unintended pregnancies are mistimed
Summary Statistics
• 3.1 million unintended pregnancies in 2001 in
the United States
• Half (49%) of all pregnancies are unintended
• Of these, 48% resulted from contraceptive
failure
• 42% of unintended pregnancies end in abortion
• 35% of births result from unintended pregnancy
• Half (48%) of women aged 15-44 have ever
had an unintended pregnancy
Finer & Henshaw. Perspect Sex Reprod Health 2006;38:90-6
% Pregnancies Unintended by Age
100%
80%
60%
40%
20%
0%
<15
15-19
20-24
25-29
30-34
35-39
>40
Finer & Henshaw. Perspect Sex Reprod Health 2006;38:90-6
% Unintended Pregnancies by Age
35%
30%
25%
20%
15%
10%
5%
0%
<15
15-19
20-24
25-29
30-34
35-39
>40
Finer & Henshaw. Perspect Sex Reprod Health 2006;38:90-6
Contraceptive Failure
Issues
•
•
•
•
Efficacy versus effectiveness
Typical versus perfect use
Results from literature
Communicating the risk of failure
Efficacy versus Effectiveness
• Efficacy: how well a method works under
ideal circumstances
• Effectiveness: how well a method works in
the real world
• Efficacy would be measured in a clinical trial
whereas effectiveness would be measured in
a survey or a chart review
Sources of Data
• Surveys: NSFG 1973, 1976, 1982, 1988, 1995, 2002
– Nationally representative
– Retrospective
– Underreporting of abortion
– Overreporting of contraceptive failure leading to birth?
• Clinical trials
– Hawthorne effect and inference beyond trial setting
– Cycles of perfect use can be identified and pregnancy
rates during perfect use can be estimated but adherence
is self-reported
Results from the 2002 NSFG:
% becoming pregnant in the first year of
use uncorrected and corrected for
underreporting of abortion
Method
Uncorrected
Corrected
Pill
7.7
8.7
Condom
13.9
17.4
FAB-methods
23.0
25.3
Kost. Contraception 2008;77:10-21
Self-Reporting of Adherence
• Self reports on missed OCs compared with
electronic recording on punched pills among
103 women for 3 cycles
• Agreement on only 45% of days
• Overreporting of no missed pills (53-59%
versus 19-33%)
• Underreporting of missing 3+ pills (10-14%
versus 30-51%)
Potter. Fam Plan Perspect 1996;28:154-8
Typical Use versus Perfect Use
• Contraceptive failure during typical use can
be measured in a clinical trial or in a survey
• Contraceptive failure during perfect use has
been measured only in clinical trials, since
retrospective reporting of adherence in
surveys is likely to be terrible
What Is Typical Use?
• By definition, a woman is a user whenever
she considers herself to be using a method
• Hence, typical use of a barrier method does
not imply that it is actually used at every act
of intercourse
• Typical use includes both inconsistent use
and incorrect use
What Is Perfect Use?
• By definition, perfect use of a method
requires actual use according to the
directions for that method
• Perfect use of a barrier method requires that
it be used correctly at every act of
intercourse
• Perfect use does not imply no pregnancies
Logical Error Ingrained in Literature
• Suppose in a contraceptive trial there are
100 years of exposure to risk of pregnancy
• 15 pregnancies occur during a cycle of
imperfect use
• 5 pregnancies occur during a cycle of perfect
use
• What is the method-related pregnancy rate
(pregnancy rate during perfect use)?
Method-Related Pregnancy Rate
• Traditional answer
– 5/100 = 5 per 100 woman-years of exposure
• Logical error
– Denominator cannot be all exposure since by
definition a method-related pregnancy can occur
only during perfect use
– If there are only 50 woman-years of perfect use,
correct answer is 5/50 = 10 per 100 womanyears of exposure
Flaw in Design of Clinical Trials
• Information on perfect (correct and consistent)
use is usually obtained only for cycles when
pregnancy occurred
• Hence, pregnancy rates during perfect use
cannot be estimated in most trials
• They are nevertheless reported, incorrectly, as
method failure rates
Correct Analysis by Cycle
P
Woman 1: █ █ █ █ █ █
P
Woman 2: █ █ █ █ █
Woman 3: █ █ █ █
Woman 4: █ █ █
P = pregnancy
Cycles: imperfect use
Rates: 1/3
perfect use
1/15
all
2/18
Factors That Influence Failure
• Inherent efficacy of the method
• Imperfect use, the extent of which will
depend on motivation to avoid pregnancy
• Frequency of intercourse, which declines
with both age and marital duration
• Individual level of fecundity, which also
declines with age
• Competence (honesty?) of the investigator
Common Problems and Errors
•
•
•
•
•
•
High percent not completing trial
Underreporting of abortion
Incorrect calculation of method failure
Not including “learning” phase
Discontinuing non-adherent women
Discontinuing women who are late for an
injection
Problems in Comparing Methods
• Results come from different sources; results
where available for typical use come from the
NSFG, adjusted for underreporting of
abortion
• Women choose which method to use and are
not randomly assigned to methods. Women
who choose to use spermicides are very
different from those who choose to use IUDs
Results from Literature
• Table 27-1 from the next edition of
Contraceptive Technology
• Estimates of the annual risk of contraceptive
failure during perfect and typical use of no
method, spermicides, withdrawal, fertility
awareness based methods, sponge,
diaphragm, male and female condom, pill,
patch, ring, injectable, IUD, implant, tubal
ligation, and vasectomy
Method
Typical Use
Perfect Use
Chance
85%
85%
Condom
17%
2%
Pill, patch, ring
9%
0.3%
Depo Provera
7%
0.3%
L
ParaGard IUD
0.8%
0.6%
A
Mirena IUS
0.2%
0.2%
R
Implanon
0.05%
0.05%
C
Method
Typical Use
Perfect Use
Chance
85%
85%
Condom
17%
2%
Pill, patch, ring
9%
0.3%
Depo Provera
7%
0.3%
ParaGard IUD
0.8%
0.6%
Mirena IUS
0.2%
0.2%
Implanon
0.05%
0.05%
What Table 27-1 Shows
• Methods requiring adherence generally show
a big difference between perfect-use and
typical-use failure rates
• The most effective methods during typical
use are those not requiring adherence
• The most effective methods are not those
that protect against STIs
Contraceptive Use
Sobering to compare the
contraceptive failure rates
to the methods actually used
Mosher. NCHS 2004; Lader. ONS 2007
Method
US-2002
UK-2006/7
Chance
11%
3%
Condom/withdrawal
20%
20%
Pill, patch, ring
28%
36%
Depo Provera
5%
4%
IUD/IUS
2%
8%
Implanon
0%
1%
Sterilization
32%
26%
Communicating Risk of Failure
• Two studies have examined
– How well do women understand contraceptive failure
rates?
– How to communicate contraceptive effectiveness?
• Result is a chart that appears in the new
WHO Global Handbook for Family Planning
Providers and the new edition of
Contraceptive Technology
Steiner. Obstet Gynecol 1996;88:24S-30S
Steiner. Obstet Gynecol 2003;102:709-17
Comparing typical effectiveness of contraceptive methods
More effective
How to make your method
most effective
Less than 1 pregnancy per 100
women in one year
After procedure, little or nothing to
do or remember
Female
Sterilization
Vasectomy
Implant
Vasectomy: Use another method for
first 3 months
IUD
Injections: Get repeat injections on
time
LAM (for 6 months): Breastfeed often,
day and night
Injectables
Pills
LAM
Patch
Ring
Pills: Take a pill each day
Patch, ring: Keep in place, change on
time
Condoms, diaphragm, sponge: Use
correctly every time you have sex
Fertility-awareness based methods:
Abstain or use condoms on fertile days.
Male
Condoms
Female
Condoms
Diaphragm
Sponge
Fertility-Awareness
Based Methods
Newest methods (Standard Days Method and
TwoDay Method) may be the easiest to use.
Withdrawal, spermicide: Use
correctly every time you have sex
Withdrawal
Spermicides
Less effective
About 30 pregnancies per 100
women in one year
Source WHO 2006, adapted with permission
Method
US-2002
UK-2006/7
Chance
11%
3%
Condom/withdrawal
20%
20%
Pill, patch, ring
28%
36%
Depo Provera
5%
4%
IUD/IUS
2%
8%
Implanon
0%
1%
Sterilization
32%
26%