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Q: female fertility ( Answered 5 out of 5 stars,   2 Comments )
Subject: female fertility
Category: Health > Women's Health
Asked by: jps2003-ga
List Price: $20.00
Posted: 21 May 2003 11:43 PDT
Expires: 20 Jun 2003 11:43 PDT
Question ID: 206889
I need to know the probabillity that a woman would become pregnant
with one-year of unprotected intercourse as a function of age.  That
is:  what is the probabillity at 20, 25, 30, 35, 40, 45.

I have found information on the web that relates to relative fertility
(relative to peak) as a function of age, but I need to know the
absolute fertility levels.

Request for Question Clarification by tehuti-ga on 21 May 2003 12:47 PDT
I can supply probability rates of conceiving within a year for the
following age groups: under 30 years, 30-40, over 40 and at 50yr. 
Will this be sufficient, or do you need exact age points you mention?

Request for Question Clarification by cynthia-ga on 21 May 2003 14:46 PDT
From scanning the table of contents, it's likely your answer is in
this PDF file, I just don't have time to find it until tomorrow.

Vital and Health Statistics, Series 21, No. 56 (1/2000)

It lists preganncy rtaes for each age group you mentionm  for a 20
year period but I need to spend more time looking to see if the rates
are specifically in a 1 year period with no contraception. Logically,
it would be but I (try!) never assume...


Clarification of Question by jps2003-ga on 22 May 2003 06:01 PDT
I don't need the exact ages, but I need more than <30 30 - 40, >40

I could live with 25 - 30, 30 - 35, 35-40, 40-45
Subject: Re: female fertility
Answered By: tehuti-ga on 22 May 2003 10:23 PDT
Rated:5 out of 5 stars
I have found a site that provides a way to calculate the predicted
pregnancy rate at one year.  This takes into account the complete
fertility status of the couple, but can also be used to get data
referring only to age. It is based on calculating the total
“infertility factor” for a couple.
“A simple predictive tool was developed in the field of fertility
medicine to predict the chance that couples who seem to be infertile
will conceive spontaneously….
The first data set (996 couples) came from a time when the large
majority of the women had not yet passed the age of 35 years.
Therefore, no reliable estimates could be made for women older than
age 35. The second data set included 751 women attending a fertility
clinic for artificial insemination, among whom 6% of the women were
older than 35 years of age. The effect of age on fertility was
estimated from this data set, which enabled the extension of the age
range to 40 years” 
From: Handbook of Medical Informatics, edited by J.H. van Bemmel,
Erasmus University, Rotterdam  M.A. Musen, Stanford University,

The part of the infertility factor relating to the woman’s age is
given in Table18.5 (follow the hyperlink), and values are also given
for other things which will influence the chances of conception, eg
motility of the partner’s sperm.  You add together as many of these as
are relevant and then go to Figure 18.2 (hyperlinked), and read off
the values for the predicted pregnancy rate after one year.  The rates
are given as fractions, but can be easily transferred into
percentages, for example, a rate of 0.5 is the same as saying there is
a 50% probability. Here are the values if only the age factor is taken
into account:

 Age                  Factor            Predicted pregnancy rate after
1 year
21-25                  0                                    83%
26-31                  2                                    77%
32-34                  4                                    72%
35-37                10                                    55%
38-40                16                                    40%
and from the source mentioned immediately below, one can estimate:
40-45                                                      25-30%
45-49                                                      25% or less
50                                                           virtually

The second estimate I found takes very broad bands for the younger
ages, however, it also gives values for over 40 and at 50 years:
“Sexually active women under 30 years of age have a 90% chance of
conceiving within a year.  Conception rate drops to 75% percent
between the ages of 30 and 40.  After the age of 40, the conception
rate drops to 25-30%, and at age 50, fertility is essentially zero. 
(Source:  Kirtly Parker Jones, MD, Chief of Reproductive
Endocrinology, University of Utah School of Medicine,
Words of Wellness, Vol. XVII, No. 5)” ('Pathways to
Wellness' web site of PEIA, the West Virginia Public Employee
Insurance Agency)

However, a press release from NIEHS in July 2002 gives much higher
figures for the probability of conception in women under 40 than
either of the above two sources.  It is based on a study of 782
couples in various parts of Europe who were trying to conceive:

”Fertility in women started to decline as early as the late 20s and
for men from their late 30s. However, this was due to declines in the
per-menstrual-cycle conception rate and not to an increase in the
proportion of couples unable to achieve an unassisted pregnancy…
Dunson said the percentage of women failing to conceive within a year
ranged from 8 percent of those between 19 and 26 years old to 13-14
percent of women between 27 and 34, and finally 18 percent for women
35 to 39.
"But regardless of age, most of the women who failed to conceive
within the first 12 cycles conceived in the next 12. Only 3 percent of
19 to 26 year olds, 6 percent of 27 to 34 year olds and 9 percent of
35 to 39 year olds failed to conceive in the second year, provided the
male partner was aged under 40," Dunson said.” 

A UK study published in 2000 found that the age of the male partner
will also have an effect on the probability of conception.
Human Reproduction, Volume 15(8), pages 1703-1708 
“Increasing paternal age is associated with delayed conception in a
large population of fertile couples: evidence for declining fecundity
in older men. The ALSPAC Study Team (Avon Longitudinal Study of
Pregnancy and Childhood).” by Ford WC, North K, Taylor H, Farrow A,
Hull MG, Golding J.
The authors’ summary is available at:
and there is another summary at:
“Women with partners five or more years older have less chance of
conceiving within a year of trying than those whose partners are the
same age, or younger. The odds of conceiving within 6 months of trying
decrease by 2% for every year that the man is older than 24 years, and
for conception within a year decrease by 3% for each year….  the study
found that in a couple who ultimately prove to be fertile, the
probability that it will take more than a year to conceive nearly
doubles from around 8% when the man is younger than 25 years, to
around 15% when he is older than 35.”

I looked at the CDC data mentioned by cynthia, but this just gives the
overall number of pregnancies that actually occurred per 1000 women of
the whole population in each age range.

Search strategy: probability conceiving year

Clarification of Answer by tehuti-ga on 22 May 2003 10:25 PDT
The formatting went wonky.  The table should have the following three headings:


Fertility Factor 

Predicted pregnancy rate after 1 year

and the value for age 50 should read: virtually 0%
jps2003-ga rated this answer:5 out of 5 stars

Subject: Re: female fertility
From: mvguy-ga on 22 May 2003 07:43 PDT
The following document shows the relationship between age and
fertility, but the figures are for given days relative to the
menstrual cycle rather than over a year:

Changes with age in the level and duration of fertility in the
menstrual cycle
Subject: Re: female fertility
From: jps2003-ga on 23 May 2003 07:53 PDT
The responses have been great, but a [problem is that the women in the
>35 sample were in fertility clinics, and what I really need
is the estimate for percentage of women who would become pregnant in a
sample of women who are NOT in
treatment for infertility.

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