Ultrasound Obstet Gynecol 2016; 48: 566–573

Published online 26 October 2016 in Wiley Online Library (wileyonlinelibrary.com). DOI: 10.1002/uog.16016

Stillbirth and intrauterine fetal death: factors affecting

determination of cause of death at autopsy
J. MAN*†, J. C. HUTCHINSON*†, A. E. HEAZELL‡, M. ASHWORTH*, S. LEVINE§
and N. J. SEBIRE*†
*Department of Histopathology, Camelia Botnar Laboratories, Great Ormond Street Hospital, London, UK; †University College London,
Institute of Child Health, London, UK; ‡Department of Obstetrics and Gynaecology, St Mary’s Hospital, Manchester, UK; §Department of
Histopathology, St George’s Hospital, London, UK

K E Y W O R D S: autopsy; intrauterine death; stillbirth etiology; unexplained

ABSTRACT could be identified from clinical review and external fetal

examination or imaging, with most of the remainder being
Objectives There have been several attempts to classify
determined following placental examination.
cause of death (CoD) in stillbirth; however, all such
systems are subjective, allowing for observer bias and Conclusions Based on objective criteria, many intrauter-
making comparisons between systems challenging. This ine deaths throughout gestation remain unexplained
study aimed to examine factors relating to determination despite autopsy examination. The rate of unexplained
of CoD using a large dataset from two specialist death varies from around 30% to 60% depending on
centers in which observer bias had been reduced by interpretation of the significance of features. CoD deter-
classifying findings objectively and assigning CoD based mination is dependent on both the classification system
on predetermined criteria. used and subjective interpretation, such that variation in
the proportion of ‘unexplained’ cases is based largely on
Methods Detailed autopsy reports from intrauterine
speculation regarding mechanisms of death. Novel meth-
deaths in the second and third trimesters during
ods to determine objectively the mechanism of death at
2005–2013 were reviewed and findings entered into a
postmortem examination are required. Copyright © 2016
specially designed database, in which CoD was assigned
ISUOG. Published by John Wiley & Sons Ltd.
using predefined objective criteria. Data regarding CoD
categories and factors affecting determination of CoD
were examined.
INTRODUCTION
Results There were 1064 intrauterine deaths, including
246 early intrauterine fetal deaths (IUFD) (< 20 weeks), The primary aim of postmortem investigation of intrauter-
179 late IUFDs (20–23 weeks) and 639 stillbirths ine death is determination of cause and mechanism of
(≥ 24 weeks’ gestation). Overall, around 40% (n = 412) death, to facilitate counseling of parents, management
had a clear CoD identified, whilst around 60% (n = 652) of subsequent pregnancies and future interventions1 – 4 .
were classified as ‘unexplained’, including around half Over the last 50 years there have been many attempts
with identified risk factors or lesions of uncertain to classify cause of death in stillbirths, but, according
significance, with the remaining half (n = 292 (45%)) to which of the more than 30 classification systems5 is
being entirely unexplained. A stepwise increase in used, a variable but significant proportion (15–60%)
the proportion of unexplained deaths was observed of stillbirths remain unexplained, despite postmortem
with increasing maceration. Black and Asian women examinations being undertaken in specialist centers6,7 .
had significantly greater proportions of deaths due to Classification systems include the Aberdeen, based pre-
ascending infection, whilst women aged over 40 years had dominantly on obstetric findings and clinical history8,9 ,
significantly increased placenta-related CoDs. There was the Wigglesworth, which subdivides cases into general
no significant difference in CoD distribution according to groups6 , the Relevant Condition at Death (ReCoDe),
maternal body mass index or with increasing postmortem which records associated risk factors7 , and the Causes
interval. Around half of those with an identifiable CoD of Death and Associated Conditions (CODAC), which

Correspondence to: Prof. N. J. Sebire, Department of Histopathology, Level 3 Camelia Botnar Laboratories, Great Ormond Street Hospital,
Great Ormond Street, London WC1N 3JH, UK (e-mail: Neil.Sebire@gosh.nhs.uk)
Accepted: 6 July 2016

Copyright © 2016 ISUOG. Published by John Wiley & Sons Ltd. ORIGINAL PAPER
Cause of intrauterine death 567

is designed to accommodate main cause of death and only the final subjective opinion of the initial reporting
associated conditions10 (the latter two systems recording pathologist. For example, ‘abruption’ was defined as a
apparent growth restriction as a specific cause of stillbirth recorded history of clinical abruption with or without
based on varying criteria). concurrent placental or autopsy findings; ‘ascending infec-
Each system has advantages and disadvantages and no tion’ was histologically proven chorioamnionitis with or
perfect system exists, the major consideration being the without funisitis with or without fetal pneumonia; ‘birth
underlying purpose for which the data will be used. A trauma’ was a documented complication that occurred
review of classification systems reported that the best per- during delivery leading to fatal intrapartum event, with
forming, in terms of ease of use, interobserver agreement consistent autopsy findings; ‘congenital abnormality’ was
and lowest rate of ‘unexplained’ deaths was CODAC11 . a congenital abnormality documented at autopsy, which
However, all such systems, especially when based on likely accounted for the death; ‘cord accident’ was a wit-
population or registry data, are subjective, thus allowing nessed and recorded cord complication during delivery,
bias and making useful comparisons between systems such as cord prolapse (the isolated postmortem finding of
challenging. There are several explanations for the differ- changes such as cord knot or abnormal coiling at autopsy
ences in reported frequencies of ‘unexplained’ stillbirths, in the absence of specific clinical history or other findings
including that classification systems may include events was not considered a definite cause of death); ‘placental’
that were not causally related to the stillbirth. Whilst it was significant and definite abnormal placental patholog-
is tempting to suggest that reducing unexplained cases is ical findings present which likely caused the death, e.g.
beneficial, this is true only if there is definitive evidence severe maternal vascular malperfusion, chronic histiocytic
that the ‘cause’ assigned is correct; in practice, the sig- intervillositis (placental histological changes of uncertain
nificance of factors in individual cases can be difficult to clinical significance such as mild changes suggestive of
assess. impaired maternal vascular perfusion, low-grade villitis
The aims of this study were to examine factors relating of unknown etiology and intervillous thrombi, and
to determination of cause of death using a large dataset non-specific cord changes such as coiling index, were not
extracted from an autopsy research database including included in this category). In cases in which no definitive
cases from two specialist centers, in which observer bias cause of death was identified, the case was classified, for
was reduced as far as possible by recording objectively the purposes of this study, as ‘unexplained’. However, in
findings at autopsy and assigning causes and classifications order to allow further analysis, these cases were further
of death based on predetermined criteria. subclassified as follows: ‘unexplained lesion, fetus’ was
defined as an unexplained cause of death, but in the
presence of a fetal finding of unknown significance (e.g.
METHODS
mild intraventricular hemorrhage only); ‘unexplained
This analysis was part of a larger study examining lesion, clinical’ was in the presence of a clinical risk
autopsy findings in intrauterine deaths, based on an factor known to increase stillbirth risk but of unknown
established Microsoft Access autopsy research database significance in the specific case (e.g. maternal cholestasis
(Microsoft Corp., Redmond, WA, USA) which includes or diabetes mellitus); ‘unexplained lesion, cord’ was in
details of all autopsies performed from 2005 to 2013 the presence of a cord finding of unknown significance
inclusive from Great Ormond Street Hospital and (e.g. true cord knot but with no thrombosis or other
additional cases of stillbirth autopsies from St George’s pathological findings); ‘unexplained lesion, placenta’
Hospital, London. Clinical details, autopsy findings and was in the presence of placental findings of unknown
results of ancillary investigations were recorded (> 400 significance (e.g. villous changes such as increased syn-
variables per case) based on predefined criteria, as cytial knots, but without changes of severe malperfusion
documented in the Database Manual (Appendix S1). such as infarcts or vasculopathy or intervillous thrombi);
Intrauterine fetal deaths (IUFDs) occurring ≤ 23 weeks’ ‘unexplained, obese’ was in association with documented
gestation were recorded as second-trimester IUFDs, while maternal obesity (body mass index (BMI) > 30 kg/m2 );
those ≥ 24 weeks’ gestation were classified as stillbirths. ‘unexplained, post-term’ was in association with doc-
For the purposes of this study, detailed autopsy data umented post-term delivery (≥ 42 weeks); ‘unexplained
from all intrauterine deaths occurring during the second with previous fetal loss’ was in association with maternal
and third trimesters were reviewed and analyzed through history of previous fetal loss; ‘unexplained with diabetes’
queries and statistical tests run using Microsoft Access was in association with diabetes mellitus or gestational
and Microsoft Excel (Microsoft Corp.), GraphPad Prism diabetes; ‘unexplained, unexplained’ was no cause of
(GraphPad Software Inc., San Diego, CA, USA) and Stats death found at autopsy, no abnormal placental findings
Direct (StatsDirect Ltd., Altrincham, UK). P < 0.05 was and no clinical risk factor associations; ‘unexplained all’
considered statistically significant. was no cause of death found based on antenatal history
Strict predetermined criteria were used to assign an and autopsy findings; this category encompassed all of the
objective cause of death for each case (Appendix S1). ‘unexplained’ groups listed above. If any specific cause
Cause of death was based on definite documented findings, of death was present, this was used to classify the case,
including clinical history, macroscopic and microscopic even in the presence of underlying maternal issues such as
features and results of ancillary investigations, rather than obesity or diabetes mellitus. Maceration was defined as

Copyright © 2016 ISUOG. Published by John Wiley & Sons Ltd. Ultrasound Obstet Gynecol 2016; 48: 566–573.
568 Man et al.

Table 1 Overall cause of death, defined objectively based on autopsy findings, in a series of 1064 intrauterine deaths in the second and third
trimesters, and subdivided according to gestational age at death

Overall cause of death All (n = 1064) Early IUFD (n = 246) Late IUFD (n = 179) Stillbirth (n = 639)

Abruption 38 (4) 3 (1) 5 (3) 30 (5)

Ascending infection 176 (17) 58 (24) 59 (33) 59 (9)
Birth trauma 7 (1) 0 (0) 0 (0) 7 (1)
Congenital abnormality 50 (5) 9 (4) 5 (3) 36 (6)
Fetomaternal hemorrhage 6 (1) 0 (0) 0 (0) 6 (1)
Infection 13 (1) 0 (0) 1 (1) 12 (2)
Known cord accident* 4 (< 1) 1 (< 1) 1 (1) 2 (< 1)
Known IUGR* 17 (2) 4 (2) 5 (3) 8 (1)
Placental lesion 60 (6) 1 (< 1) 4 (2) 55 (9)
Pre-eclampsia 16 (2) 0 (0) 0 (0) 16 (3)
Preterm birth 4 (< 1) 0 (0) 3 (2) 1 (< 1)
Twin complication 21 (2) 8 (3) 4 (2) 9 (1)
Unexplained (all) 652 (61) 162 (66) 92 (51) 398 (62)
Unexplained, diabetes† 23 (2) 4 (2) 3 (1) 16 (3)
Unexplained, lesion‡ 125 (12) 19 (8) 10 (6) 96 (15)
Unexplained, maternal obesity 83 (8) 27 (11) 9 (5) 47 (7)
Unexplained, post-term 29 (3) 0 (0) 0 (0) 29 (5)
Unexplained, previous fetal loss 100 (9) 43 (17) 16 (9) 41 (6)
Unexplained, unexplained 292 (27) 69 (28) 54 (30) 169 (26)

Data are given as n (%). Early intrauterine fetal death (IUFD) was defined as intrauterine death < 20 weeks, late IUFD was death at
20–23 weeks and stillbirth was death ≥ 24 weeks. *Known to pathologist before placental examination. †Diabetes mellitus or gestational
diabetes. ‡Fetal, cord or placental lesion. IUGR, intrauterine growth restriction.

changes on external examination following intrauterine 70

retention after fetal death according to standard clinical
definitions. 60
Data were analyzed with descriptive statistics,
chi-square-based comparison of proportion testing and
50
Mann–Whitney U-test for comparison of distributions,
Percentage of cases

using StatsDirect (StatsDirect Ltd.). P < 0.05 was consid-

ered statistically significant. The study was approved by 40
the local research ethics committee.
30
RESULTS
20
The total dataset comprised 1064 intrauterine deaths
across both second and third trimesters, including 425
IUFDs ≤ 23 weeks’ gestation (246 early (< 20 weeks’ ges- 10
tation) and 179 late (20–23 weeks)) and 639 still-
births ≥ 24 weeks; the classification of final cause of death 0
in ion

na no ma

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in term psia

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in ion

for the overall group and according to gestational age

m ital h tr on

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groups is provided in Table 1 and Figures 1 and 2. Over-

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all, around 40% of cases were associated with a definite

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history and/or abnormal pathological findings at autopsy.

on

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Approximately 60% of cases, however, did not have

Cause of death
a clear cause of death identified and hence were
‘unexplained’. Of these, around half either had identified
Figure 1 Overall cause of death, with percentage prevalence,
risk factors, such as diabetes mellitus, or lesions of
defined objectively based on autopsy findings in a series of 1064
uncertain significance, whilst the remainder had no intrauterine deaths in the second and third trimesters. *Known to
abnormal features and were entirely unexplained. For pathologist before placental examination. IUGR, intrauterine
the purposes of this study, intrauterine growth restriction growth restriction.
(IUGR) was given as the cause of death for cases in
which an antenatal diagnosis of IUGR was documented pathology was identified were classified as ‘placental’.
and in which surveillance was ongoing; cases in which The issue of determination of FGR based on body
placental pathology of maternal vascular malperfusion or weight and organ weight ratios is investigated in detail
other definite fetal growth restriction (FGR)-associated elsewhere12 – 18 .

Copyright © 2016 ISUOG. Published by John Wiley & Sons Ltd. Ultrasound Obstet Gynecol 2016; 48: 566–573.
Cause of intrauterine death 569

35 Cause of death in the majority of cases was

unexplained across all ethnic groups, but black and
Asian mothers had significantly greater proportions of
30 deaths due to ascending infection (Table S1, Figure 3;
z = 7.4, P < 0.0001 and z = 2.4, P = 0.08, respectively).
The majority of the study population (77%) had a
25 maternal age ≤ 35 years with the majority of deaths being
unexplained regardless of maternal-age group (Table S2,
Percentage of cases

Figure 4; z = 1.27, P = 0.21). However, mothers over

20
the age of 40 had a significantly increased frequency of
placental causes of death (z = 2.33, P = 0.02). There was
15
no significant difference in cause of death distribution
according to maternal BMI; in particular, unexplained
deaths had similar frequencies regardless of maternal BMI
10 category (Table S3, Figure 5, z = 0.73, P = 0.46).
There was no significant effect of postmortem interval
(time from delivery to postmortem examination) on
5 determination of cause of death (Figure 6), with propor-
tion of unexplained cases being similar at all intervals
(z = 0.48, P = 0.63). Fetuses with unexplained deaths
0 were significantly more macerated than were those with
em rm a

other causes of death (z = 9.24, P < 0.0001) and there

m ni ir fe on
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was a stepwise increase in the proportion of unexplained

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deaths with increasing severity of maceration (Table

a
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S4, Figure 7); even when cases of ascending infection

sc

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were excluded from the analysis, cases with unexplained

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deaths were significantly more macerated than were those

ne

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with other causes of death (z = 3.4, P < 0.0001). Finally,

U

Cause of death
when using predetermined objective criteria to determine
cause of death from the findings of the pathologist, there
Figure 2 Simplified cause of death, based on autopsy findings, in
1064 cases of intrauterine death, according to gestational age at was no significant effect of the particular pathologist
death: intrauterine fetal death < 23 weeks ( ) and stillbirth performing the autopsy (Figure 8), the proportion of
≥ 24 weeks ( ). *Known to pathologist before placental unexplained cases being similar across all pathologists
examination. IUGR, intrauterine growth restriction. (χ2 = 3.28, P = 0.06).
In order to compare our findings with published data,
‘Unexplained’ cases represented the largest category we applied the ReCoDe classification system, using cal-
regardless of gestational age. Placental pathologies, culations of unadjusted birth-weight centile to determine
i.e. placental abruption, placental histological the proportion of cases that were small-for-gestational
abnormalities19 and unexplained cases with placen- age (SGA, < 10th centile of the normal liveborn range).
tal lesions, were significantly more common in stillbirths These cases were coded as equivalent to ‘A7 Fetal Growth
compared with IUFDs (z = 2.4, P = 0.02; z = 5.1, Restriction’ according to the ReCoDe system and grouped
P < 0.0001; and z = 2.4, P = 0.019, respectively). Ascend- together with cases diagnosed with antenatal IUGR. (SGA
ing infection and unexplained death with a history of cases could only be calculated for fetuses > 23 weeks of
fetal loss were significantly more common in second gestation with documented birth weight; the total number
trimester IUFDs than in stillbirths (z = 7.8, P < 0.0001; of cases that could be classified using the ReCoDe system
and z = 4.1, P < 0.0001, respectively). No other cause was 529.) Using this classification system, 37% of deaths
of death categories had significant differences between were SGA (similar to the 43% reported in a previous
gestational-age groups. series of stillbirths in the UK7 ).
There were 81 cases with some form of ‘limited’ Around 20% of all deaths could be classified based
autopsy based on parental consent requirements (52 with primarily on the antenatal history, clinical events, ante-
external examination with postmortem cross-sectional natal ultrasound scan findings or external examination
imaging and placental examination only; 22 with stan- (for example, congenital anomalies, documented acute
dard autopsy but limited to specific body cavities; and placental abruption). Placental histological examination
seven with only postmortem imaging followed by organ identified the cause of death in a further 18%. Invasive
sampling only. Of these limited examinations, cause autopsy examination with organ sampling provided the
of death in 51 (63%) was unexplained, a proportion specific cause of death in only 1–2% of cases20 . The
not significantly different from the overall percentage remainder of the deaths in the study population were
of unexplained deaths (62%); thus for the analysis all unexplained, with invasive examination providing limited
autopsies were reported as one group. additional diagnostic information (Figure 9).

Copyright © 2016 ISUOG. Published by John Wiley & Sons Ltd. Ultrasound Obstet Gynecol 2016; 48: 566–573.
570 Man et al.

80
70

Percentage of cases
60
50
40
30
20
10
0
n

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Cause of death

Figure 3 Cause of intrauterine death in 752 cases according to maternal ethnicity: white ( ), mixed/Oriental ( ), Asian ( ) or black ( ).
Black and Asian mothers had a significantly greater proportion of deaths associated with ascending infection than did white mothers.
*Known to pathologist before placental examination. IUGR, intrauterine growth restriction.

70

60

50
Percentage of cases

40

30

20

10

0
n

ity

ia

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ag
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Cause of death

Figure 4 Cause of intrauterine death in 1039 cases according to maternal age: ≤ 35 years ( ), 36–40 years ( ) or ≥ 41 years ( ). There were
significantly more placenta-related causes of death in mothers over 40 years of age. *Known to pathologist before placental examination.
IUGR, intrauterine growth restriction.

DISCUSSION dependent on the classification system used; reduction in

the proportion of ‘unexplained’ cases across studies may
The findings of this study have potentially important
be based on speculation regarding mechanisms of death.
implications for both clinical practice and epidemiological
Finally, maceration changes which occur after death are
research studies in stillbirth and IUFD. First, using
associated with decreased frequency of identification of
objective criteria to classify cause of death, many
intrauterine deaths remain unexplained regardless of specific cause of death at autopsy but there is no effect
gestational age, despite full autopsy examination by of increasing interval between delivery and postmortem
specialist pathologists. Second, the rate of unexplained examination on determination of the cause of death.
death can vary from around 30% to 60% according Based on a predefined, objective hierarchical classifi-
to the interpretation of, and significance attributed to, cation, around 60% of intrauterine deaths were unex-
features in the clinical history, autopsy and placental plained, despite autopsy examination being performed;
examination, despite objective findings being similar. around half of these were associated with no clinical, fetal
Third, the cause of death provided both clinically or placental lesions, being entirely unexplained, while
and in population-based studies is variable and highly the remainder showed either associated risk factors or

Copyright © 2016 ISUOG. Published by John Wiley & Sons Ltd. Ultrasound Obstet Gynecol 2016; 48: 566–573.
Cause of intrauterine death 571

80
70

Percentage of cases
60
50
40
30
20
10
0
n

ity

ia

ll)
ag
m
tio

tio

io

nt

sio

rt

io
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(a
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bi
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Cause of death

Figure 5 Cause of intrauterine death in 466 cases according to maternal body mass index (BMI) category27 : underweight ( ), < 18 kg/m2 ;
normal ( ), 18–24 kg/m2 ; overweight ( ), 25–29 kg/m2 ; obese ( ), ≥ 30 kg/m2 . No association between specific causes of intrauterine death
and maternal BMI was observed. *Known to pathologist before placental examination. IUGR, intrauterine growth restriction.

70
60
Percentage of cases

50
40
30
20
10
0
n

ity

ia

ll)
ag
m
tio

io

io

nt

io

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io
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(a
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Cause of death

Figure 6 Cause of intrauterine death in 1039 cases according to duration of time between delivery and postmortem (postmortem interval
(PMI)): 1–4 days ( ), 5–8 days ( ), 9–12 days ( ), 13–16 days ( ) or ≥ 17 days ( ). There was no significant effect of PMI on
determination of overall cause of death. *Known to pathologist before placental examination. IUGR, intrauterine growth restriction.

findings of uncertain significance. These proportions are on clinical registry data. Until objective novel laboratory
largely in keeping with those in other studies; depending criteria are available to determine or confirm specific
on which classification system is used, one to two thirds of mechanisms of death, these issues cannot be resolved.
intrauterine deaths are unexplained, the proportion being The second commonest cause of death overall
dependent on whether particular features are interpreted was ascending infection, representing 17% of the
as being sufficient to have caused the death21 . Differences total population, similar to that reported in other
in cause of death reported across studies, centers and studies22 – 24 . One previous study reported that the rate
classification systems are therefore likely related to of chorioamnionitis, both preterm and term, increased in
differences in subjective interpretation of findings rather all ethnicities over a 15-year period, with white mothers
than differences in objective findings at autopsy. In this having a lower relative risk than other ethnicities25 . The
study, strict criteria were used regarding cause of death present data confirm that black and Asian mothers have
(both regarding FGR as cause of death and interpretation a significantly greater proportion of deaths associated
of placental findings; for example, isolated cord features, with ascending infection and that ascending infection is a
such as possible abnormal coiling, were not regarded major cause of non-macerated late second-trimester IUFD.
as a cause of death here). This strict approach allowed In general, other demographic factors, such as maternal
objectivity and consistency, with findings of only possible age and obesity, showed little association with specific
significance being categorized as unexplained; this likely causes of IUFD, other than there being a significantly
explains the relatively high frequency of apparently greater frequency of placental pathologies in mothers
unexplained cases compared with historical studies based over 40 years of age. There are few comparable published

Copyright © 2016 ISUOG. Published by John Wiley & Sons Ltd. Ultrasound Obstet Gynecol 2016; 48: 566–573.
572 Man et al.

80
Clinical event, history or clinical
70 US, external or imaging 20%
examination (20%)
60
Percentage of cases

50 38%

40 Placental examination
(18%)
30

20
39%
10
Autopsy
0
None Mild Moderate Severe
Degree of maceration

Figure 7 Percentage of unexplained intrauterine deaths according Cause of death found

to degree of fetal maceration, categorized as mild, moderate or (1%)
100%
severe following Genest and Singer28 (n = 533). A stepwise increase
in unexplained deaths was seen with increasing maceration (which
Unexplained
persisted even when deaths due to ascending infection were
n = 652 (61%)
removed from the analysis).

80
Percentage of cases unexplained

70 Figure 9 Proportion of cases that were allocated a cause of death

using clinical history, antenatal ultrasound (US) or postmortem
60
imaging/external examination (20%), placental examination (18%)
50 or autopsy (1%) and those remaining unexplained (61%).

40
examination and histological sampling, an alternative
30 explanation may be that cases with retention following
20
intrauterine death were less likely to be associated with
a clear clinical history or specific event. There was no
10 association between postmortem interval and determina-
0 tion of cause of death, demonstrating that delay between
A B C D E delivery and autopsy, even of many days, does not affect
Pathologist the likelihood of determining a cause of death, providing
that bodies are refrigerated suitably; this factor should
Figure 8 Percentage of intrauterine deaths that were unexplained, not affect decisions regarding investigation after death.
by pathologist performing the autopsy. When predefined criteria
were used based on objective autopsy findings, there was no
In order to allow comparison with published data, cases
significant difference in rate of unexplained deaths between were classified using ReCoDe; this resulted in many more
pathologists. deaths becoming ‘attributed’ to FGR (37%), based purely
on fetal weight at delivery (although there are method-
data regarding maternal demographic factors and specific ological flaws with this approach)17 . Nevertheless, around
causes of intrauterine death across gestation; one study one third of cases remained unexplained even using the
examined national stillbirth data and reported increased ReCoDe classification. These findings demonstrate the dif-
risk of term stillbirth among mothers ≥ 35 years of age due ficulty in comparing data across classification systems even
to major fetal congenital abnormalities, maternal medical when the same dataset is being assessed, due to the sub-
disorders and obstetric mechanical causes26 . jective nature of categorization and difficulty in interpre-
There was an association between maceration, indicat- tation of the significance of factors in an individual case7 .
ing an extended intrauterine interval between death and In around 20% of cases, the cause of death could
delivery, and apparently unexplained death. A relation- be identified from careful clinical review, fetal external
ship between proportion of unexplained deaths and wors- examination/imaging and placental examination. Tra-
ening maceration was noted, suggesting a possible effect ditional invasive autopsy examination itself determined
on the ability to identify the cause of death at autopsy. the cause in a minority of cases, most remaining unex-
One confounding factor could be ascending infection, plained if the placental findings and clinical history were
since this leads to onset of labor with intrapartum death non-contributory. Hence, the majority of published data,
of a non-macerated fetus, but this does not account for the which include the final composite of all aspects of the
effect since the association remained even once ascending postmortem examination, overestimate the role of internal
infection was excluded, suggesting a genuine association examination and sampling in cases of intrauterine death.
with maceration. However, as only a small proportion However, it should be emphasized that such examination
of all cases had a cause of death identified by internal may provide evidence supporting a given diagnosis, may

Copyright © 2016 ISUOG. Published by John Wiley & Sons Ltd. Ultrasound Obstet Gynecol 2016; 48: 566–573.
Cause of intrauterine death 573

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SUPPORTING INFORMATION ON THE INTERNET

The following supporting information may be found in the online version of this article:
Appendix S1 Database manual
Tables S1–S4 Cause of intrauterine death according to maternal ethnicity (Table S1), maternal age (Table S2),
maternal body mass index (Table S3) and fetal maceration (Table S4)

Copyright © 2016 ISUOG. Published by John Wiley & Sons Ltd. Ultrasound Obstet Gynecol 2016; 48: 566–573.
Ultrasound Obstet Gynecol 2016; 48: 566–573
Published online 26 October 2016 in Wiley Online Library (wileyonlinelibrary.com). DOI: 10.1002/uog.16016

Éxitus fetal y muerte fetal intrauterina: factores que influyen en la determinaci ón de la causa de
la muerte en la autopsia

RESUMEN
Objetivos Ha habido varios intentos de clasificar la causa de la muerte (CM) en éxitus fetal. Sin embargo, todos estos
sistemas son subjetivos, lo cual posibilita sesgos del observador y hace difı́ciles las comparaciones entre sistemas. Este
estudio tuvo como objetivo examinar los factores relacionados con la determinación de la CM mediante un conjunto
de datos extensos de dos centros especializados en los que el sesgo del observador se habı́a reducido mediante la
clasificación de los hallazgos de manera objetiva y la asignación de la CM con base en criterios predeterminados.
Métodos Se revisaron informes detallados de autopsias de muertes intrauterinas en el segundo y tercer trimestre durante
2005–2013 y los hallazgos se introdujeron en una base de datos especialmente diseñada, en la que la CM fue asignada
utilizando criterios objetivos predefinidos. Se examinaron los datos relativos a las categorı́as de la CM y los factores
que afectan a su determinación.
Resultados Hubo 1064 muertes intrauterinas, entre ellas 246 muertes fetales intrauterinas (MFI) tempranas (<20
semanas), 179 MFI tardı́as (20–23 semanas) y 639 éxitus fetales (≥24 semanas de gestación). En general, la CM
se identificó claramente en alrededor del 40% (n=412), mientras que alrededor del 60% (n=652) se clasificó como
‘‘sin explicación’’, y entre estas últimas alrededor de la mitad con factores de riesgo identificados o lesiones con
significado incierto, y la mitad restante (n=292 (45%)) totalmente sin explicación. Se observó un aumento gradual en la
proporción de muertes sin explicación con el aumento de la maceración. Las mujeres de raza negras y asiáticas tuvieron
significativamente una mayor proporción de muertes debidas a infección ascendente, mientras que las mujeres mayores
de 40 años tuvieron significativamente más CM relacionadas con la placenta. No hubo diferencias significativas en la
distribución de CM de acuerdo con el ı́ndice de masa corporal de la madre o con el aumento del intervalo post mortem.
En alrededor de la mitad de los fetos con una CM identificable, la causa se pudo identificar a partir de una revisión
clı́nica y de imágenes o examen fetal externo, y en la mayorı́a del resto se determinó mediante el examen de la placenta.
Conclusiones Basados en criterios objetivos, muchas muertes intrauterinas durante la gestación permanecen sin
explicación a pesar de la autopsia. La tasa de muertes sin explicación varı́a en alrededor del 30% al 60%, dependiendo
de la interpretación de lo significativo de las observaciones. La determinación de la CM depende tanto del sistema
de clasificación utilizado como de la interpretación subjetiva, de modo que la variación en la proporción de casos sin
explicación se basa en gran medida en especulaciones sobre los mecanismos de la muerte. En el examen post mortem se
requieren nuevos métodos para determinar objetivamente el motivo de la muerte.

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