Accuracy of perception of ovulation day in women trying to conceive

Abstract

The likelihood of conception is increased if intercourse is timed to coincide with the fertile period (5 days up to ovulation). However, to be effective, this requires good awareness of the day of ovulation. The aim of this study was to examine the accuracy of women's perceived ovulation day, compared with actual fertile days, in a cohort of women trying to conceive.
Comparison of women's estimated day of ovulation with their actual ovulation day (determined by detecting luteinising hormone).
This was a sample collection study and volunteer women were recruited via online advertising. At recruitment volunteers reported the cycle day they believed they ovulated. They then used a home urine fertility monitor to test their daily fertility status to time intercourse to try and achieve conception, in addition to collecting early morning urine samples for laboratory analysis. The main outcome measure was a comparison of women's estimated day of ovulation with their actual ovulation day, as determined by urine detection of luteinising hormone.
Three hundred and thirty women were recruited onto the study and data was available for 102 volunteers who became pregnant. Thirteen women (12.7%) correctly estimated their ovulation day; median difference +2 days, range -10 to +27 days. The most common days for estimation of ovulation were day 14 (35.5%) and day 15 (15.7%). Only 55% of estimated ovulation days fell within the volunteers' fertile window; only 27% on days of peak fertility.
Women trying to conceive may benefit from using a prospective method to identify their fertile phase, as a significant proportion could be incorrectly estimating their fertile days. These observations were made on women who were actively looking for knowledge on fertility and considered only cycles where conception occurred, inaccuracy could be greater if a broader population is considered.

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Current Medical Research & Opinion Vol. 28, No. 5, 2012, 1–6
0300-7995 Article FT-0065.R1/681638
doi:10.1185/03007995.2012.681638 All rights reserved: reproduction in whole or part not permitted
Original article
Accuracy of perception of ovulation day
in women trying to conceive
Michael Zinaman
Tufts University School of Medicine, Boston, USA
Sarah Johnson
SPD Swiss Precision Diagnostics Development Co.
Ltd, Bedford, UK
Jayne Ellis
Alere International, Cranfield, UK
William Ledger
University of New South Wales, Royal Hospital for
Women, Sydney, Australia
Address for correspondence:
Sarah Johnson, PhD, Clinical and Medical Affairs
Manager, SPD Development Company Limited,
Priory Business Park, Bedford, MK44 3UP, UK.
Tel.: þ44 (0)1234 835 486;
Fax: þ44 (0)1234 835 006;
sarah.johnson@spdspark.com
Keywords:
Clearblue – Conception – Cycle variability – hCG – LH
surge – Menstrual cycle length – Ovulation –
Pregnancy – Timing of ovulation
Accepted: 27 March 2012; published online: 18 April 2012
Citation: Curr Med Res Opin 2012; 28:1–6
Abstract
Background:
The likelihood of conception is increased if intercourse is timed to coincide with the fertile period (5 days up
to ovulation). However, to be effective, this requires good awareness of the day of ovulation. The aim of this
study was to examine the accuracy of women’s perceived ovulation day, compared with actual fertile days,
in a cohort of women trying to conceive.
Main outcome measures:
Comparison of women’s estimated day of ovulation with their actual ovulation day (determined by detecting
luteinising hormone).
Methods:
This was a sample collection study and volunteer women were recruited via online advertising. At
recruitment volunteers reported the cycle day they believed they ovulated. They then used a home urine
fertility monitor to test their daily fertility status to time intercourse to try and achieve conception, in addition
to collecting early morning urine samples for laboratory analysis. The main outcome measure was a
comparison of women’s estimated day of ovulation with their actual ovulation day, as determined by
urine detection of luteinising hormone.
Results:
Three hundred and thirty women were recruited onto the study and data was available for 102 volunteers
who became pregnant. Thirteen women (12.7%) correctly estimated their ovulation day; median difference
þ2 days, range 10 to þ27 days. The most common days for estimation of ovulation were day 14 (35.5%)
and day 15 (15.7%). Only 55% of estimated ovulation days fell within the volunteers’ fertile window; only
27% on days of peak fertility.
Conclusions:
Women trying to conceive may benefit from using a prospective method to identify their fertile phase, as a
significant proportion could be incorrectly estimating their fertile days. These observations were made on
women who were actively looking for knowledge on fertility and considered only cycles where conception
occurred, inaccuracy could be greater if a broader population is considered.
Introduction
For successful conception, intercourse must occur within a window that spans
five days prior to ovulation and ends on the estimated ovulation day
1
. If a woman
has an increased awareness of her most fertile time, it will increase the likelihood
of conception
2–4
. Therefore timing intercourse to coincide with the fertile
period is a simple method which can maximise the chances of natural concep-
tion. However, to be effective, timed intercourse requires a good awareness of
the day of ovulation
5
.
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The use of hormonal monitoring methods to detect the
luteinising hormone (LH) surge in plasma or urine pro-
vides a means to prospectively identify the time of peak
fertility and eliminates the uncertainty of attempting to
pinpoint ovulatory timing via either calendar extrapola-
tions of previous cycle lengths
6,7
, or less reliable physio-
logical methods such as basal body temperature and
cervical mucus evaluation
8
. The LH surge is one of the
most accurate and reliable markers of impending ovula-
tion, with ovulation occurring 24–36 hours after the LH
surge
6,9–12
.
Women who are trying to conceive may decide to use
any combination of these methods to try to identify their
fertile days, and so begin to develop an awareness of when
these days are in the cycle. However, if a prospective mon-
itoring method is not used, then inter-cycle follicular
phase variability will impact how accurately they are
able to estimate these days. In this study, we examined
the accuracy of perceived day of ovulation in women
attempting to conceive, compared with their actual fertile
days, using urinary hormone monitoring.
Patients and methods
Design
This study was a prospective cohort study, which ran
between July 2008 and February 2009. This study enabled
investigation of women’s knowledge of their menstrual
cycle length characteristics and ovulatory timing by com-
paring their reported cycle length history and estimated
ovulation day with actual cycle lengths and ovulation days,
as determined via urinary hormonal monitoring. Ethical
approval for this study was obtained from the local Ethics
Committee and all study volunteers provided written
informed consent.
Subjects
Women seeking conception (n¼330) were recruited from
across the UK via an advert on the UK Clearblue website
and had to meet the following inclusion criteria: aged
18–45 years at recruitment; not breast feeding; shortest
cycle 422 days and longest 539 days in the previous 6
months; at least three normal cycles since discontinuation
of hormonal contraception (not taking any medication or
using contraception that could impact their normal men-
strual cycle, e.g. HRT, OCP, Mirena, etc.). Any women
testing positive for pregnancy (Clearblue home pregnancy
test (HPT), SPD Swiss Precision Diagnostics GmbH),
prior to their first menstrual cycle on the trial were
ineligible.
Study protocol
At recruitment, the participants were asked their average
cycle length, their shortest remembered cycle length, their
longest remembered cycle length, and the day of their
cycle on which they thought they ovulated. Participants
were not afforded any assistance when answering the first
three questions and were asked to provide their ‘best esti-
mate’ if they were unsure. They were permitted to answer
‘not known’ to the question concerning their ovulation
date. Data on prior experience of using home ovulation
tests was also collected. These admission results were con-
sidered as the woman’s knowledge of her menstrual cycle.
Volunteers were provided with a home urine fertility
monitor (Clearblue Fertility Monitor, SPD Swiss Precision
Diagnostics GmbH) and urine test sticks that measure
levels of both luteinising hormone (LH) and the oestrogen
metabolite, oestrone-3-glucoronide (E3G), to provide
users with daily information on their fertility status (low,
high and peak fertility), in order for them to appropriately
time intercourse to try and achieve conception.
Volunteers also collected daily early morning urine sam-
ples into bar-coded, childproof containers containing
sodium azide as preservative. Samples were stored by vol-
unteers at 4C and sent to the study centre once the stor-
age container was full (maximum 15 samples). Daily
diaries were also completed for each cycle, recording
menses, monitor usage and medications and were returned
to the study centre on completion of each cycle.
Laboratory analysis
The day of the LH surge was identified in the laboratory
using a home ovulation test (Clearblue Home Ovulation
Test, SPD Swiss Precision Diagnostics GmbH) and was
confirmed by quantitative LH measurements using
AutoDelfia (Perkin Elmer). It was also corroborated
against volunteer diary entries. In addition, pregnancy
was confirmed in the laboratory using HPT and quantita-
tive hCG measurement (AutoDelfia) on the daily urine
samples 15 days following LH surge, for all cycles where
conception occurred.
Results
The average menstrual cycle length reported by volunteers
on admission to the study was 29 days. The average actual
cycle length was calculated for volunteers who failed to
become pregnant in the first cycle (n¼273), and was also
found to be 29 days. However, the range in actual first
cycle length (22–54 days) was considerably greater than
that reported by the non-pregnant volunteers in cycle 1
(24–37 days). One hundred and thirty women conceived
during the study. The pregnancy rate was 17% for cycle 1;
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by cycle 3, 33% of the 330 volunteers had become preg-
nant, and by cycle 6, 42% had become pregnant.
One hundred and two (78.5%) of the pregnant volun-
teers had provided an estimate of their day of ovulation.
Demographic details for these 102 women are presented in
Table 1. The mean age of these women was 30.6 years
(SD 4.63). Seventy-one women (69.6%) had used a
home ovulation test prior to study entry.
Compared with women who had not used home ovula-
tion tests (HOTs) prior to the start of the study, a signif-
icantly higher proportion of HOT users were able to
answer the question: ‘On what day of your cycle do you
think you ovulate?’ (88.8% [95% CI: 80–95%] HOT users
versus 62.0% [95% CI: 47–75%] non-HOT users;
p¼0.0003).
Day 15 (15.7%) and day 14 (35.3%) were the most
common responses for women’s estimated day of ovula-
tion. No women believed they ovulated earlier than day
9 or later than day 25 (Figure 1A). The study population’s
laboratory-calculated actual ovulation days ranged from
day 9 to day 44. Only 19.6% of the women had a calculated
day of ovulation of either day 14 (2.0%) or day 15 (17.6%)
(Figure 1B).
Only 13 women (12.7%) correctly predicted their day
of ovulation, of which 8 (62%) had previously used HOTs,
which is comparable to the number of previous HOT users
recruited to the study (69.6%). A further 39 women
(38.2%) estimated their ovulation day within 1 day
and 57 women (55.9%) estimated their ovulation day
within 2 days. The range of estimated versus actual ovu-
lation days spanned from 10 (i.e. ovulation occurred 10
days earlier than expected) to þ27 (i.e. ovulation occurred
27 days later than expected) (Figure 2) with the median
difference being þ2 days (i.e. the actual ovulation day was
a median of 2 days later than the estimated ovulation day).
We attempted to ascertain whether HOT users were more
accurate in their prediction of day of ovulation than non-
HOT users. Although 51.6% of non-HOT users were more
than 2 days out, either way, with their ovulation-day pre-
diction, compared to 39.4% for the HOT user cohort, the
study numbers were too low to statistically confirm this
hypothesis.
When considering whether the women’s estimation of
day of ovulation would have resulted in intercourse on a
day where pregnancy was possible, only 54.9% (Table 2)
would have targeted a day within their fertile window (the
3 days preceding LH surge, day of LH surge and day fol-
lowing the LH surge [calculated day of ovulation]) and
only 26.5% would have targeted their time of peak fertility
(day of LH surge and the following day).
Discussion
This study, conducted on women seeking to become preg-
nant, found that the majority of women who were able to
estimate their day of ovulation thought that they ovulated
on day 14. The dominance of day 14 may indicate that
women are relying on the text book definitions of a men-
strual cycle, rather than understanding their own actual
cycles. Women who had previously used home ovulation
tests were more likely to provide an answer to the question
‘On what day of your cycle do you think you ovulate?’ indi-
cating that their use had provided some degree of educa-
tion and awareness regarding their menstrual cycles.
Overall, only 56% of women estimated their day of
ovulation correctly within a margin of 2 days in the
Table 1. Demographic characteristics of the 102 women who conceived
during the study and who predicted their ovulation day.
Characteristic (n¼102 women)
Age
a
Mean (SD) 30.6 (4.63)
Median 30.5
Quartiles (lower, upper) 28, 34
Minimum, maximum 20, 41
Average cycle length reported at recruitment (days)
Mean (SD) 29.0 (2.50)
Median 28
Quartiles (lower, upper) 28, 30
Minimum, maximum 23, 35
How long have you been trying to conceive? (months)
Mean (SD) 8.1 (6.73)
Median 6
Quartiles (lower, upper) 3, 12
Minimum, maximum 0, 38
No. of women % of women
(n¼102)
Age group
b
18–25 14 14%
26–30 38 37%
31–35 35 34%
36–40 13 13%
41–45 2 2%
Number of previous pregnancies
None 21 21%
1 40 39%
2 20 20%
3 12 12%
4399%
Highest qualifications achieved
None 2 2%
GCSE or NVQ 13 13%
HNC/A levels 46 45%
Degree 23 23%
Postgraduate 17 17%
Other 1 1%
Occupation
Professional 24 24%
Office/administration 37 36%
Other 41 40%
Ever used a home pregnancy test
Yes 99 97%
Ever used a home ovulation test
Yes 71 70%
a
Age is calculated as at day 1 of cycle 1.
b
Age group is from subject history form completed at recruitment.
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cycle in which they conceived. When considering whether
this would have enabled timing of intercourse to a fertile
day, only 26.5% would have targeted their most fertile days
and 54.9% would have identified a day where pregnancy
was possible. This was probably due to two important fac-
tors: a lack of awareness of their own menstrual cycle char-
acteristics and their own intra-cycle variability. The
average menstrual cycle length variability is around 7
days
13,14
, with the majority of this variability attributable
to the follicular phase. The only way to correct for this
normal variability is to employ a method that can accu-
rately and prospectively detect the fertile phase within any
given cycle. Such methods include home ovulation tests,
the dual-hormone fertility monitoring device used by the
women in this study (i.e. the Clearblue Fertility Monitor),
or cervical mucus observations. This point is emphasised
by the observation that, ovulation leading to conception
occurred as early as day 9 or as late as day 44, which would
20 Ovulation day earlier than expected
Ovulation day estimated correctly
Ovulation day later than expected
-10 -8 -6 -4 -2 0 2 4 6 8 10 12 14 >=16
Estimated ovulation day - ovulation day reported at recruitment
15
10
Percentage of women
5
0
Median
Quartiles
Min, Max
2 days later
0, 4 days later
-10, +27 days
Figure 2. The difference between the 102 women’s expected ovulation day and actual ovulation day in the cycle in which they conceived. The actual
ovulation day occurred on the woman’s expected ovulation day in fewer than 13% of instances.
Percentage of women
Laboratory-calculated day of ovulation
>=272513 15 17 19 21 23
C
y
cle da
y
reported as da
y
of ovulation
911 >=272513 15 17 19 21 23911
0
(A) (B)
40 40
Median day 14 Median day 16
Quartiles day 14, 16 Quartiles day
15,19
30 Min, Max day 9,25 30 Min,
Max
day
9,44
20
Percentage of women
20
10 10
0
Figure 1. A: Range of estimates from the 102 (78%) women who answered the question: On what day of your cycle do you think you ovulate? Fifty-one per
cent of these women believed they ovulated either on day 14 or day 15. No women believed they ovulated earlier than day 9 or later than day 25. B: Range of
‘actual’ ovulation days as calculated via laboratory analysis for the study’s 102 conception cycles. In all cases, the day after the LH surge, as measured by the
Clearblue Ovulation Test (and confirmed by quantitative LH measurements using AutoDelfia (Perkin Elmer), was calculated as the day of ovulation. Ovulation
was found to occur as early as day 9 or as late as day 44.
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be extremely difficult to predict without a prospective
method. It is unlikely that this observation is unusual as
the average and range of menstrual cycle length seen in
these volunteers was consistent with other studies
13,14
and
mean age of these women was 30.6 years (SD 4.63) con-
sistent with the UK average age in pregnancy of 29.5
15
.
The cycle length characteristics seen in this study are
strikingly similar to that reported by other authors
13,16
.
However, one interesting observation in this study is the
small number of women whose calculated day of ovulation
(day following LH surge) in their conception cycle was
actually day 14. This is likely to be due to our relatively
small study cohort, although other authors have made sim-
ilar observations. Baird et al. reported that only 10% of
women with regular 28-day menstrual cycles ovulated on
day 14
17
; furthermore, the most logical conclusion for a
study which found that the human gestational period was
283 (rather than 280) days, is that ovulation on days 15–17
is typical and not delayed
18
.
In this study, only 19.6% of women ovulated on day 14
or 15 of their cycle and the actual ovulation day was on
average 2 days later than estimated (Figure 2).
Misjudgement of their actual ovulation day could there-
fore be one reason why the women in this study had been
trying to conceive for an average of 8 months prior to the
study (Table 1). This is considerably longer than observed
in women using fertility awareness methods
19
. As these
women were able to conceive on this study when using a
fertility monitor, it suggests that incorrect timing may
have been a factor in why these women had previously
failed to conceive. Accurate prediction of ovulation
using home ovulation tests or fertility monitors is thus a
useful aid for women trying to get pregnant and could
shorten the time to conception
5,8,17
.
Mistiming of intercourse is a primary reason for failure
to conceive
5
, and although conception-seeking couples are
usually advised to increase their coital frequency, for many
couples, this is neither desirable or achievable
20
. Use of a
home ovulation test or dual-hormone fertility monitor can
accurately detect the LH surge that immediately precludes
ovulation
10,21
. This enables women to accurately predict
their ovulation date themselves, without expensive labo-
ratory tests or ultrasound examinations
22,23
. However, for
some women, these home tests may still be unaffordable.
Cervical mucus monitoring or noting cervical position can
both be used to prospectively identify the fertile period,
although often training is required and these methods can
be of lower accuracy
8
.
An important limitation of this study is that it studied
women recruited via an advertisement on a pregnancy/fer-
tility focused website, which is likely to have biased
recruitment towards those seeking more information to
assist with conception. As these women are taking an
active interest in conception it would be expected that
they would be more knowledgeable about their menstrual
cycle than those less actively planning a pregnancy. Also
the analysis only considered cycles in which conception
actually occurred, therefore the findings relate to truly fer-
tile cycles. It is likely that, if non-conceptual cycles were
included, there would be increased variability of menstrual
cycle characteristics, thus women’s perception of their
menstrual cycle characteristics could be less accurate if
these cycles were also considered.
Conclusion
Women trying to conceive may benefit from using a pro-
spective method to identify the fertile phase, as a signifi-
cant proportion could be incorrectly estimating their
fertile days and so incorrectly timing intercourse in order
to conceive.
Transparency
Declaration of funding
This study was funded by SPD Swiss Precision Diagnostics
GmbH.
Declaration of financial/other relationships
S.J. has disclosed that she is an employee of SPD Development
Company Ltd, UK. J.E. has disclosed that she is a former
employee of SPD Swiss Precision Diagnostics GmbH,
Switzerland. M.Z. and W.L. have disclosed that they have
received honoraria from, and provide ongoing consultancy,
to SPD Development Company Ltd.
CMRO peer reviewers may have received honoraria for their
review work. The peer reviewers on this manuscript have dis-
closed that they have no relevant financial relationships.
Acknowledgements
The authors would like to thank IMC Healthcare
Communication, funded by SPD Swiss Precision Diagnostics
GmbH, for their assistance in preparing this manuscript.
Previous presentation: ACOG 59th Annual Clinical Meeting,
Washington, USA, 30 April–4 May 2011.
Table 2. Proportion of women (n¼102) whose estimate of day of ovulation
would mean that they would time intercourse to coincide with their fertile
window: peak 2 days (day of LH surge and LH surge þ1), three most fertile
days (day preceding surge, day of LH surge, LH surge þ1), four most fertile
days (2 days before, day of LH surge, LH surge þ1), full fertile window
(3 days preceding surge, day of surge, LH surge þ1).
Number of women Percentage of women
Peak 2 days 27 26.47
Three most fertile days 40 39.22
Four most fertile days 49 48.04
Full fertile window 56 54.90
LH: luteinising hormone.
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