J Assist Reprod Genet (2011) 28:699–705
DOI 10.1007/s10815-011-9583-z
ASSISTED REPRODUCTION TECHNOLOGIES
A meta-analysis of the impact of IVF and ICSI on major
malformations after adjusting for the effect of subfertility
Alfred A. Rimm & Alyce C. Katayama &
K. Paul Katayama
Received: 25 March 2011 / Accepted: 13 May 2011 / Published online: 31 May 2011
# Springer Science+Business Media, LLC 2011
Abstract
Objective To estimate the effect of assisted reproductive
technology (ART) on major malformation (MM) rate in ART
offspring independent of the effect of subfertility on MM.
Design Meta-analysis.
Methods This meta-analysis is based on our previously
published meta-analysis of observational studies evaluating
the relationship between ART treatment and MM rates, as
well as recent research by Zhu et al. to estimate the impact
of subfertility alone on MM in subfertile couples conceiving
spontaneously.
Results The overall odds ratio for MM in our original metaanalysis, in which all studies used apparently inappropriate
control groups of “normal” populations, was 1.29 (95% CI
1.01–1.67). Here we attempted to estimate the risk of
subfertility and used this estimate to perform an adjusted
meta-analysis. Zhu et al. found that about 40% of the odds
Capsule This study attempts to separate the risk of major
malformation in ART offspring attributable to subfertility from the risk
attributable to ART. After adjusting for subfertility, we found no
increased risk.
A. A. Rimm (*)
Department of Epidemiology and Biostatistics,
Case Western Reserve University School of Medicine,
Room WG-57, 10900 Euclid Avenue,
Cleveland, OH 44106–4945, USA
e-mail: alfred.rimm@case.edu
A. C. Katayama
Health Law Group, Quarles & Brady LLP,
Milwaukee, WI, USA
K. P. Katayama
Department of Obstetrics and Gynecology, University of
Wisconsin School of Medicine and Advanced Institute of Fertility,
Milwaukee, WI, USA
of MM was due to subfertility. When we took Zhu’s finding
into account, the adjusted odds ratio in the meta-analysis
was 1.01 (95% CI 0.82–1.23).
Conclusions Our study suggests ART does not increase the
risk of MM as much as previously reported. More research
is needed to quantify the underlying risk of subfertility and
separate it from the risk associated with ART. Physicians
who counsel subfertile couples should recognize that
previous studies of MM rates in ART patients probably
overestimated the risk.
Keywords Subfertility and major malformations . ART
outcomes . Meta-analysis . IVF/ICSI outcomes
Introduction
The safety of IVF and ICSI, sometimes referred to as
assisted reproductive technology (ART), is a matter of
critical importance to patients and practitioners. To investigate one aspect of safety, we published a meta-analysis of
observational studies in 2004 evaluating the relationship
between in vitro fertilisation (IVF) and intra cytoplasmic
sperm injection (ICSI) (together referred to herein as ART)
and major malformations (MM) in the offspring [1]. The
details of the meta-analysis—including the literature search,
the study selection and the data extraction processes—are
described there. We found 19 studies [2–20] for inclusion in
the meta-analysis and found that ART increased the risk of
MM with an odds ratio of 1.29 (95% CI 1.01–1.67). Our
major conclusion was that the risk we found may be
inflated by the fact that none of the studies used the most
appropriate control group, namely subfertile couples conceiving spontaneously. Instead, each study used a control
group of either a general population or a hospital specific
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“normal” cohort. Thus the risk found did not take into
account the possibility that subfertile couples could be at an
increased risk of MM in part because of the various
underlying causes of their subfertility. Control groups made
up of almost all normal couples do not consider this
possibility. Lack of appropriate control groups in studies of
risk associated with ART continues to be an issue. For
example, as recently as 2009, the CDC published a report
estimating the increased risk of certain congenital malformations in ART offspring at 2.0 to 4.0 [21]. The study
lacked an appropriate control group [22].
While many studies have focused on the risks of ART
treatment, actually separating that risk from the risk associated
with the couples’ underlying subfertility has seldom been
attempted for any outcomes in the offspring. However, many
investigators [23–27] have suggested that underlying subfertility may have an impact on ART outcomes, separate
from the putative impact of the ART treatment itself.
In 2006, Zhu et al. [28] conducted a study that
responded to our study regarding inappropriate control
groups. They examined the effect of subfertility on MM
rates, using the Danish national birth cohort. They studied
MM rates in couples who conceived after less than
6 months, 6 to 12 months, and more than 12 months of
attempting to conceive. They collapsed the scale to a binary
grouping: ≤12 and >12 months. This is consistent with the
widely accepted view that subfertility is “a disease of the
reproductive system defined by the failure to achieve a
clinical pregnancy after 12 months or more of regular
unprotected sexual intercourse” [29].
When Zhu et al. compared the fertile couples who
conceived in 12 month or less to the subfertile couples,
an increased risk of MM of 1.20 (95% CI 1.07–1.35)
was found. When couples receiving IVF or ICSI (ART)
were compared to the same group of fertile couples, an
increased risk of MM of 1.50 was found (weighted
average). This suggests that subfertility contributes close
to 40% of the increased risk of MM that is observed in
the offspring of ART-treated subfertile couples. Zhu et al.
also observed that the overall prevalence of congenital
malformations increased with increasing time to pregnancy (TTP). Zhu’s results support our suggestion and
that of other investigators [30–32] that only subfertile
couples are an appropriate control group for ART outcome
studies because subfertility, with all its underlying causes,
itself creates a risk of MM and other outcomes of concern.
Materials and methods
Since the Zhu study apparently gives the first estimate of
the effect of the underlying subfertility on MM risk, that
estimate was used to adjust our meta-analysis in a
J Assist Reprod Genet (2011) 28:699–705
quantitative effort to account for the subfertility effect
separate from the ART treatment effect. The literature was
searched for other studies where estimates of MM rates
were presented for subfertile couples. No studies were
found, other than Zhu’s, which could be used to estimate the
effect of underlying conditions on MM in subfertile couples.
The literature was also searched to determine whether any
other studies since 2006 had attempted to adjust MM odds
ratios based on Zhu’s findings; none were found.
In this review of the 19 studies used in our original metaanalysis, one study was found to have a problem with the
control group. After correspondence with the author about
this problem, the study had to be excluded from our metaanalysis. Before this change, the OR with the 19 studies
was 1.29 (95% CI 1.01–1.67). With the 18 remaining
studies, using our original methodology, the corrected OR
is 1.14 (95% CI .94–1.4).
Using the findings of Zhu’s study, the 18 studies in our
meta-analysis were reanalyzed in order to derive an overall
estimate of the results that might have been obtained if proper
control groups had been used in those studies. Based on the
fact that Zhu’s results showed ART increased the risk of MM
about 50% and subfertility increased it 20%, it was assumed
that subfertility is the cause of about 40% of the overall
increased risk of MM observed in ART offspring. Therefore,
the odds ratio in each study was reduced by 40%. For
example, when the odds were 1.5, it was reduced to 1.30.
When the odds were less than 1.0, which suggested a
protective effect, an adjustment was obtained by subtracting
the odds from 1.0, taking 40% of this difference, and then
subtracting that difference from the observed odds ratio. For
example, if the odds were .90, this was subtracted from 1.0,
giving .10. Forty percent of .10, or .04, was subtracted from
.90, giving an adjusted odds of .86.
The 95% confidence intervals (CIs) were obtained by the
following method. For each study, the adjusted odds ratio was
first obtained and then used to solve for the number of
malformed infants in the ART group that would be expected
if the number of infants with MM due to subfertility were
eliminated from the numerator of the ART group. Using the
adjusted numerator in the ART group, the adjusted 95% CIs
were then calculated. The adjusted 95% CIs were very similar to
the original 95% CIs in our meta-analysis. The random effects
model was used in the meta-analysis. A fixed effect model was
also used and the results were found to be almost identical to the
results when the random effects model was used.
Reducing the odds ratio for each study by 40% is the
conservative method of trying to adjust out the malformations as a result of subfertility. A less conservative method
was also used; this entailed reducing the odds ratio for each
study by the absolute value of .19. This is derived from the
odds ratio of 1.19 for MM found in Zhu’s study for
subfertile couples who conceived spontaneously. In this
J Assist Reprod Genet (2011) 28:699–705
analysis, the random effects model was used, but the forest
plot is not presented because it is almost identical to that
obtained when the 40% reduction in the odds is used.
Results
Figure 1 is a forest plot of the odds ratios and 95% CIs for
the 18 studies in our original meta-analysis, after adjusting
for the risk of subfertility by reducing the odds of each
study by 40%.
Table 1 shows the unadjusted odds ratios in each of the
18 studies from our meta-analysis as well as the adjusted
odds ratios for each study. The original overall odds ratio
from our published meta-analysis of the 19 studies was 1.29
and statistically significant. When the one study with an
error in the control group was eliminated, the odds ratio for
the remaining 18 studies was 1.14 (95% CI 0.94–1.4).
When the odds ratio of each of the 18 studies was
reduced by 40%, the adjusted overall odds ratio was 1.01
(95% CI 0.82–1.23). The rather low overall adjusted OR of
1.01 is due to the fact that some of the larger studies had a
protective effect before adjustment and the analysis weights
studies according to their sample size. This is our best
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Table 1 Originally Publisheda and Adjusted Odds Ratios of the
Association Between ART and Major Malformations
Reference &
study typeb
Originally
published
odds ratio
Significance
Adjusted
odds ratio
Significance
4C
12 V
2C
18 V
20 V
0.54
0.81
0.77
0.86
0.90
P<.05
NS
NS
NS
NS
0.38
0.59
0.64
0.79
0.84
P<.05
P<.05
NS
P<.05
NS
15 V
13 V
3X
19 C
9V
6V
16 V
7V
10 X
17 V
5X
8C
14c V
1.00
1.04
1.07
1.24
1.21
1.19
1.29
1.25
1.27
1.38
2.05
2.23
NS
NS
P<.05
NS
NS
P<.05
NS
NS
P<.05
NS
P<.05
P<.05
1.00
1.02
1.05
1.07
1.11
1.12
1.13
1.17
1.18
1.18
1.69
1.82
NS
NS
NS
NS
NS
NS
NS
NS
P<.05
NS
P<.05
P<.05
15.4
1.14e
NS
P<.05
5.4
1.01
NS
NS
Overall Odds
Ratiod
a
18 of the original studies are shown here; as explained in the text,
one study has been removed.
b
Reference numbers refer to references in this publication, not the
original publication. V: IVF Study; X: ICSI Study; C: Combined
Results of ICSI and IVF.
c
No MM in control group; when .5 is substituted for zero, the
adjusted OR is 5.4.
d
Since the odds ratios in our meta-analysis were not significantly
different for IVF versus ICSI and for singleton versus multiple, the
data were pooled to obtain an overall odds ratio.
e
Overall odds when 18 studies included.
estimate, at this time, of the overall risk of MM in ART
patients when the effect of subfertility is removed. In an
alternative approach to using the results from Zhu’s study,
which found that subfertile couples who conceived spontaneously had an odds of 1.19 for MM, we subtracted the
absolute value of .19 from each of the 18 studies. This
resulted in an overall odds ratio of 0.93 (95% CI .73–1.18),
suggesting a protective effect of ART.
Discussion
Fig. 1 Forest Plot of Odds shows the adjusted Odds Ratios and
Confidence Intervals for the 18 studies. V: IVF Study; X: ICSI Study;
C: Combined Results of ICSI and IVF; white diamond: Overall Odds
Ratio. The reference number for each study is given in parentheses
Risk associated with subfertility
Is it reasonable to think that subfertile patients would have
underlying conditions that may predispose them to poor
702
pregnancy outcomes? There is a great deal of evidence in
the literature to support this view. While it is beyond the
scope of this paper to catalog all prior efforts to answer this
question, a few should be noted. Past investigators have
looked at this issue with regard to preterm delivery (PTD),
low birth weight (LBW) and perinatal mortality. Saunders
et al. [23] appears to have been the earliest in the post IVF
era. Their findings were published in a preliminary report
on the first 2 years of statistics from the Australian IVF
Register. They found that the PTD rate in singleton
pregnancies both for IVF patients and for subfertile couples
conceiving spontaneously while on the IVF waiting list
(10.0%) exceeded that of the general population (6.2%).
The incidence of LBW among singletons was also elevated
in the IVF group (6.5%) and in the spontaneously
conceiving group (8.7%) when compared to the general
population (4.8%).
In 1992 Bhalla et al. [24], 1994 Joffe et al. [25], and
1997 Henriksen [26] made important additions to the
efforts to quantify the risk of subfertility. Bhalla reported
a significantly (p <0.01) higher rate of PTD in a group of
112 subfertile (at least 2 years to conception) patients
who conceived spontaneously (28.1%) when compared to
normal controls (12.6%). Joffe reported in a populationbased study that a delay in time to conception was a risk
factor for poor obstetric outcomes, regardless of medical
intervention. Pregnancies that ended in PTD among
women who took more than 12 months to conceive
tended to take 18% longer to conceive than other live
births in the population-based cohort. Henriksen reported
that when compared to women who conceived in
6 months or less, women who tried for more than
12 months and conceived spontaneously without infertility
treatment had a significantly increased risk for PTD of 1.6
(95% CI 1.0–2.7).
In 1999, Draper et al. [30] carried out a populationbased case control study of perinatal deaths. They found
that a history of subfertility in the index pregnancy,
irrespective of treatment, increased the risk of perinatal
death, with odds of 2.9 (95% CI 1.8–4.5). Compared to the
infants of women without subfertility, the infants of
women with untreated subfertility had an increased risk
of perinatal death with odds of 3.3 (95% CI 1.6–6.8). In
the treated subfertile group, there was also an increased
risk of perinatal death, but the odds ratio was lower, 2.7,
suggesting that treatment provided a protective effect.
There are also, as described by Park et al. [33], genetic
causes of subfertility in parents known to be associated
with congenital anomalies in a baby, such as constitutional chromosomal rearrangements, including reciprocal
and robertsonian translocations and inversions. Even with
a normal karyotype there is the possibility of subtelomeric rearrangement or interstitial chromosomal dele-
J Assist Reprod Genet (2011) 28:699–705
tions and duplications. Gonadal mosaicism in a parent is
another possibility. Maternal stress could also play a role
[34].
Time to pregnancy
Since increasing TTP is associated with a risk of adverse
outcomes in the offspring, it is important to know where
ART patients fall on the TTP spectrum. When reporting on
ART treatment, TTP is seldom reported, but investigators
often cite the duration of subfertility (DOS) in the
presenting patients.
DOS is known to be significantly higher in patients
achieving pregnancy through ART treatment. Several
relatively recent studies from developed countries report
this. Poikkeus reported a DOS of about 4 years in a Finnish
IVF patient group [35]. Kupka reported a DOS of about
5 years in a large German study [36]. Thum reported a DOS
of 3.3 years in an English patient group [37]. Boivin
reported a DOS of 4.1 years among Danish couples
undergoing IVF treatment [38].
It is fair to conclude that ART patients are rather far out
on the TTP spectrum and by and large well beyond a TTP
of 12 months. Therefore, our assumption that almost all
ART couples would have conceived beyond 12 months is
reasonable, and maybe a conservative one.
Protective effect
Does the protective effect of ART, as observed in 5
studies in our meta-analysis of 18 studies, have a basis
in reality? There is some possibility that a protective
effect may arise in the ART clinic laboratory where a
variety of sperm and embryo selection processes occur.
These range from pre-implantation genetic diagnosis
(PGD) to various objective and subjective ways in
which the embryologist attempts to identify the “best”
gametes and embryos. For example, when male factors
are present and ICSI is used, several criteria—including
the proximity of appearance to normal in terms of
morphology and motility, as well as other criteria—are
used to select from among the available sperm. Poorer
quality embryos may not develop to the blastocyst
(6–8 cell) stage typically used for embryo transfer today.
When a patient has multiple embryos available, those
judged to be the “best” are transferred to the uterus first.
Finally, inferior embryos that are cryopreserved at a
patient’s request for use in a subsequent attempt to
achieve pregnancy may be the ones that do not survive
freezing and thawing.
Successful treatment may also provide protection, since
it interrupts or cuts short the TTP for the subfertile couple,
and thus avoids some delay. A prolonged TTP has been
J Assist Reprod Genet (2011) 28:699–705
shown in several studies, in addition to Zhu’s, to increase
risk. For example, Basso and Olsen [31] reported that the
risk of neonatal death was significantly increased in all
women with a TTP of greater than 12 months, OR 2.82
(95% CI 1.35–5.90), with the OR being 3.32 (95% CI
1.47–7.53) among those who had reported not receiving
infertility treatment and 2.32 (95% CI 0.86–5.80) among
those who reported treatment. Though the lower increased
risk in the treated group is not statistically significant, it
suggests the possibility of a protective effect.
Basso and Baird [32] found that an increasing TTP was
associated with significantly increased risk of preterm
(less than 37 weeks) delivery (PTD). In all primiparous
women (treated or untreated) with a TTP of greater than
12 months, the OR for preterm birth was 1.38 (95% CI
1.14–1.69); in the untreated-only subset, the OR was very
similar at 1.36 (95% CI 1.08–1.71). They concluded that
the increased risk of preterm birth observed in this group
could not be attributed solely to the effects of infertility
treatment.
Furthermore, if TTP is longer, the patient will be older
when conception occurs. Thus shortening TTP reduces the
patient’s age at the time of conception. General population
data in the U.S. have long shown the impact of maternal
age on the rate of congenital defects. The incidence is
approximately 2.7% at age 26 and by age 37 it is 3.35%
[39]. Data from France also shows that as maternal age
advances, the frequency of aneuploidy in the oocytes also
increases [40].
Strengths and weaknesses of this study
One strength of our study is that our approach to the
adjustment may be considered conservative compared to
other adjustment methodologies. For example, we could
have used the overall odds ratio of 1.29 from our metaanalysis and assumed that this 29% increase in the
incidence of MM was the truth and that subfertility
increased the incidence of MM 20%. Had we used this
approach, we would have reduced the odds in each study in
the original meta-analysis by 69% (.20÷.29=69%) rather
than 40%.
In support of the 40% risk reduction we have used here
is the fact that it is in general agreement with the level of
risk posed by subfertility alone as reported in other studies
of risks both before and since Zhu’s paper. For example,
Sun et al. reported that the risk of epilepsy was 1.71 in the
ART group and 1.38 (95% CI 1.0–1.89) in the spontaneously conceiving subfertile group [41].
Our study also benefits from the strengths of Zhu’s
study: namely a large cohort; the collection of TTP data
prior to the birth; and the fact that, in Denmark, subfertile
couples have access to up to three free IVF treatments,
703
which eliminates most of the concern about skewing of the
spontaneously conceiving group to lower socioeconomic
status than the ART-treated group.
A weakness in our study stems from the fact that
Zhu’s group only had data for spontaneous conceptions
before and after a 12 month TTP. Thus using their
estimate of the impact of underlying subfertility on the
MM rate may underestimate the effect of duration of the
underlying conditions causing infertility. In other words,
couples who try for 24 or 36 or more months before
conceiving spontaneously may be at greater risk of MM
than those who conceive at, say, 18 months. If the
distribution of couples in Zhu’s study did not represent
the world experience—if, for example, it had an excess
of couples who conceived between 12 to 15 months—
using his results could underestimate the MM risk of
underlying subfertility.
Another weakness in our study stems from the fact
that the underlying causes of subfertility may differ to
some extent between treated couples and those who
manage to conceive spontaneously. For example, some
infertile couples, with absent or blocked fallopian tubes
who procreate through ART could never conceive
spontaneously [42].
Conclusion
Our adjusted analysis suggests that the relative risk of MM
in the offspring of ART treated couples is 1.01 and not
statistically significant. It may be that with regard to MM,
ART is safer than originally thought.
These results can also be described in terms of the
actual incidence of MM. The risk of MM in the general
U.S. population is 3% [43]. Our original (corrected)
analysis, which showed an OR of 1.14, suggests an
incidence of 3.42% for MM among ART offspring. Our
adjusted analysis with an OR of 1.01 among ART treated
patients suggests that the incidence of MM among ART
treated patients is 3.03%. Though the change in incidence
is small, a discussion of the increased risk with a patient
can now be based on a study where an effort has been
made to take into account the effect of subfertility on
MM.
This analysis raises an important question about the
exact magnitude of the effect of the underlying conditions
in subfertile patients on the MM rate observed after ART
treatment and points to the need for further studies. The
literature contains studies with odds ratios that vary at least
between .55 and 7.69. It is hoped that future well-designed
studies will narrow the range and that the meta-analysis of
such studies will give a better estimate of the effect of ART
on MM.
704
Acknowledgement This work was supported in part by the
Department of Epidemiology and Biostatistics at Case Western
University School of Medicine.
J Assist Reprod Genet (2011) 28:699–705
19.
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