OBJECTIVE:
To determine the rate of histologic fetoplacental inflammation in fetuses and newborns with fatal perinatal Group B-Streptococcus (GBS) infection.
STUDY DESIGN:
Autopsy files (1990 to 2002) were searched for fetuses and newborns with
GBS-positive post-mortem blood and/or lung cultures. The rate of histological fetoplacental inflammation in preterm (<36 weeks gestational age) and term (
Z
36 weeks) fetuses/infants was compared using w 2 test.
RESULTS:
GBS infection was diagnosed in 4.9% (61/1236) of perinatal autopsies and was considered the exclusive cause of death in 58 cases (16 to 41 weeks gestation, median: 26 weeks). A total of 43 fetuses/infants (74%) were preterm, 24 (41%) were male and 33 (57%) stillborn. The histologic fetoplacental inflammatory response was age-dependent for the following variables: acute chorioamnionitis
(seen in 67% of preterm vs 33% of term fetuses/infants, p < 0.05), multiplevessel umbilical vasculitis (37 vs 7%, p < 0.05), funisitis (37 vs 13%, p <
0.05), and the presence of neutrophils in the gastrointestinal tract (35% vs none, p < 0.05). Neutrophils in the pulmonary airspaces (47 vs 33%) and pneumonia (16 vs 27%) were found with similar frequency in both groups.
CONCLUSION:
Histologic fetoplacental inflammation is a poor indicator of perinatal
GBS infection; the sensitivity is 67% in preterm and 33% in term fetuses/ newborns (overall sensitivity 59%). The higher rate of histologic inflammation in preterm fetuses/newborns suggests age-specific interactions between microorganism, host and placenta.
Journal of Perinatology (2004) 24, 441–445. doi:10.1038/sj.jp.7211129
Published online 13 May 2004
INTRODUCTION
Several lines of evidence have suggested a strong association between acute placental inflammation and neonatal bacterial infection. More than four decades ago, Benirschke
1 and Blanc
2 have demonstrated that neutrophilic inflammation of the placental membranes, chorionic plate and umbilical cord is associated with bacterial inflammation of the amniotic fluid. Subsequent studies have determined that acute placental inflammation correlates with neonatal bacterial infection, with the risk of neonatal sepsis being commensurate with the severity of inflammation.
3 – 7
More recently, a direct correlation has been demonstrated between the severity of placental inflammation and the levels of fetal/neonatal inflammatory mediators such as interleukin-6 (IL-6).
8–12
Most studies defining the association between histologic placental inflammation and neonatal infection have focused on the risk of infection in fetuses or newborns with histologic inflammation, thus addressing the question: ‘‘What is the risk of having amniotic fluid infection /neonatal infection/systemic inflammatory response in fetuses or newborns with histologic placental inflammation?’’ While these studies have determined the specificity of placental inflammation as marker of neonatal infection, they did not give much insight into its sensitivity .
(‘‘What is the rate of placental inflammation in fetuses/newborns with neonatal infection?’’)
The validity of placental inflammation as marker for intrauterine infections, an issue with major clinical and medicolegal implications, remains poorly defined at present. The aim of this study was to determine the sensitivity of histologic inflammation as a predictor of neonatal infection. Hereto, we have studied the rate of fetoplacental inflammation in a uniform autopsy series of fetuses and newborns with perinatal Group
B-Streptococcus (GBS) infection, the leading cause of invasive bacterial disease in the neonatal period.
13
Department of Pathology, Women and Infants Hospital and Brown Medical School, Providence
RI, USA.
Address correspondence and reprint requests to Monique E. De Paepe, MD, Department. of
Pathology, Women and Infants Hospital, 101 Dudley Street, Providence, RI 02905, USA.
Journal of Perinatology 2004; 24:441–445 r 2004 Nature Publishing Group All rights reserved. 0743-8346/04 $30 www.nature.com/jp
MATERIALS AND METHODS
Case selection
We performed a retrospective analysis of the Perinatal Autopsy database at Women and Infants Hospital (1990 to 2002), as approved by the institutional review board. Autopsy files of the
Division of Perinatal Pathology were searched for fetuses or newborns with perinatal GBS infection, based on post-mortem right atrial and lung cultures positive for GBS. The autopsy records were scrutinized to ensure that the GBS infection was exclusively
441

De Paepe et al.
Histologic Fetoplacental Inflammatory Response implicated as cause of death, allowing the designation of ‘‘fatal perinatal GBS infection’’.
The study was limited to fetuses and newborns with positive post-mortem cultures. Cases suggestive of, but not conclusive for,
GBS infection (such as positive placental cultures and/or positive maternal cultures in the absence of positive fetal/neonatal cultures) were excluded. Newborns living more than 48 hours were excluded as well, as the postnatal situation after such a long time interval may not reflect the in utero situation.
Histopathological analysis
The presence/absence and severity of acute inflammation in placenta and fetal tissues were recorded. Routine tissue samples taken from the placenta included two full-thickness sections of placental parenchyma, a section of a membrane roll including the site of membrane rupture, and sections from the proximal and distal parts of the umbilical cord. Hematoxylin–eosin-stained paraffin sections of the membranes, chorioamnionic plate and cord were examined microscopically.
Sections were evaluated for the presence and severity of neutrophilic infiltrates in the extraplacental membranes and chorionic plate (‘‘acute chorioamnionitis’’). The severity of histopathological inflammation was assessed using the Women and
Infants Hospital scoring system,
14 with some modifications. This simple protocol grades the intensity of the neutrophilic infiltrate on the free membranes or chorionic plate in the area of greatest density and categorizes the inflammation as mild, moderate or marked, as follows: one to ten neutrophils per high power field: mild chorioamnionitis; 11 to 50 neutrophils per high power field: moderate chorioamnionitis; higher concentrations of neutrophils: marked chorioamnionitis. The higher grade of inflammation of the amnion/chorion in the membranes and in the chorionic plate was designated as the degree of chorioamnionitis. Inflammation of the umbilical cord was scored based on the number of vessels involved and the presence of involvement of the perivascular
Wharton’s jelly (‘funisitis’). Histopathological analysis was performed by a single perinatal pathologist without knowledge of the clinical background.
Sections of lung, taken from all lobes, were studied for the presence of neutrophils within the airspaces. True fetal or neonatal pneumonia was defined as the presence of interstitial or peribronchial neutrophil infiltrates, usually in association with lymphoid aggregates. Sections of stomach, small and large intestine were studied for the presence of luminal neutrophil aggregates.
Statistical analysis
The rates of fetoplacental inflammation in preterm (< 36 weeks gestation) fetuses/newborns were compared with those of term
(
Z
36 weeks) fetuses/newborns using a w
2
-test. A p -value of < 0.05 was considered statistically significant.
442
RESULTS
Clinical features
A review of the perinatal autopsy files of Women and Infants
Hospital between 1990 and 2002 yielded 61 cases of perinatal GBS infection, as defined by positive post-mortem lung and/or blood cultures. This represents 4.9% of the total perinatal autopsy population (61/1236). Three cases of perinatal GBS infection were excluded from this study because GBS infection may not have been the exclusive cause of death: in two cases, GBS infection was associated with placental abruption and in one case with multiple congenital anomalies. In the remaining 58 cases, further described as ‘fatal GBS infection’, GBS infection was the only factor implicated in death.
The gestational age of these fetuses/newborns ranged from 16 to
41 weeks (median: 26 weeks). A total of 43 fetuses/infants were preterm (< 36 weeks gestation, median age: 23 weeks); and 15 were term (
Z
36 weeks, median age: 40 weeks). Of the 58 cases,
24 (41%) were male and 33 (57%) stillborn.
Histopathological analysis of placenta
Acute chorioamnionitis (acute inflammation of the placental amniotic membranes, virtually always associated with acute inflammation of the chorionic plate) was identified in 59% of cases
(Table 1); (Figure 1). The rate of placental inflammation in GBS infection was age-dependent: acute chorioamnionitis was seen in
29/43 (67%) of preterm infants, but only in 5/15 (33%) of term infants ( p < 0.05, w
2 test). Furthermore, the acute chorioamnionitis tended to be more severe in preterm than in term fetuses/infants (Table 1).
Vasculitis of the umbilical cord was identified in 25/58 (43%) of all cases (Table 2). The rate of multiple-vessel vasculitis (involving not only the vein, but also one or both arteries) was significantly higher in preterm infants than in term fetuses/infants (37% in preterm vs 7% in term, p < 0.05). Similarly, funisitis (extension of inflammation into Wharton’s jelly) was almost three-fold more prevalent in preterm placentas than in term placentas (37 vs 13%, p < 0.05) (Figure 1).
Table 1 Histologic chorioamnionitis in GBS-positive perinatal autopsies
Histologic chorioamnionitis Preterm n ¼ 43
Term n ¼ 15
Total n ¼ 58
Absent
Present
Mild
Moderate
Severe
14 (33%)
29 (67%)
5 (12%)
6 (13%)
18 (42%)
10 (67%)
5 (33%)*
1 (7%)
2 (13%)
2 (13%)
24 (41%)
34 (59%)
6 (10%)
8 (14%)
20 (35%)
Values represent number (and percentage) of GBS-positive term and preterm fetuses/ infants with histologic chorioamnionitis.
* p < 0.05 vs preterm ( w
2
-test).
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Histologic Fetoplacental Inflammatory Response De Paepe et al.
Table 2 Histologic cord inflammation in GBS-positive perinatal autopsies
Preterm n ¼ 43
Term n ¼ 15
Total n ¼ 58
Vasculitis
None
One-vessel
Two-vessel
Three-vessel
Funisitis
Absent
Present
22 (51%)
5 (12%)
2 (5%)
14 (32%)
11 (73%)
3 (20%)
1 (7%)
0 (0%)*
33 (57%)
8 (14%)
3 (5%)
14 (24%)
27 (63%)
16 (37%)
13 (87%)
2 (13%)*
40 (69%)
18 (31%)
Values represent number (and percentage) of GBS-positive term and preterm fetuses/ infants with histologic inflammation of the umbilical cord.
* p < 0.05 vs preterm ( w
2
-test) (for vasculitis, values compared include two- and three-vessel vasculitis).
Figure 1.
Acute inflammation of placenta. ( a ) Neutrophilic infiltrates in placental membranes (acute chorioamnionitis), marked.
( b ) Neutrophilic infiltrates in wall of umbilical vessel (vasculitis) with extension to perivascular Wharton’s jelly (funisitis). ( a , b ): Hematoxylin–eosin stain, magnification 10.
Table 3 Histologic fetal inflammation in GBS-positive perinatal autopsies
Preterm n ¼ 43
Term n ¼ 15
Total n ¼ 58
Neutrophils in airspaces
Pneumonia
Neutrophils in GI tract
20 (47%)
7 (16%)
15 (35%)
5 (33%)
4 (27%)
0 (0%)*
25 (43%)
11 (19%)
15 (26%)
Values represent number (and percentage) of GBS-positive term and preterm fetuses/ infants with histologic evidence of inflammation in lungs or gastrointestinal tract.
* p < 0.05 vs preterm ( w
2
-test).
Histopathological analysis of lungs and gastrointestinal tract
The autopsy tissues were reviewed with special attention to the lungs and gastrointestinal tract as known sites of inflammatory evidence in perinatal infections. The proportion of fetuses/infants with neutrophils within the pulmonary airspaces was similar in the preterm and term groups (47% in preterm vs 33% in term, difference not statistically significant) (Table 3; Figure 2).
Pneumonia, defined as the presence of confluent interstitial neutrophilic infiltrates, usually associated with lymphoid aggregates, was present in 27% of term fetuses and 16% of preterm fetuses (difference not significant) (Figure 2). Neutrophils were detected in the gastric and/or intestinal lumen of 15/43 (35%) of preterm, but in none of term fetuses/infants (Figure 2). Nearly all preterm fetuses/infants with gastrointestinal neutrophils also had pulmonary neutrophils (14/15).
Virtually all infants/fetuses with fetal inflammation (pulmonary neutrophils) had associated placental inflammation (19/20
Journal of Perinatology 2004; 24:441–445
Figure 2.
Acute inflammation of fetal tissues. ( a ) Neutrophilic aggregates in airspaces (newborn, 24 weeks). ( b ) Pneumonia, characterized by neutrophilic aggregates in airspaces and mixed inflammatory infiltrates in the interstitium (newborn, 28 weeks).
( c ) Neutrophils in gastrointestinal tract (fetus, 26 weeks).
( a – c ): Hematoxylin–eosin stain, magnification 40 ( a and b ),
20 ( c ).
preterm, 4/5 term). Conversely, 19/29 preterm and 10/10 infants/ fetuses with acute chorioamnionitis showed neutrophils within the pulmonary airspaces.
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Histologic Fetoplacental Inflammatory Response
COMMENT
In this study, we have determined the rate of histologic fetoplacental inflammation in an autopsy series of fetuses and infants with fatal perinatal GBS infection. GBS infection, defined by
GBS-positive post-mortem lung and/or blood cultures, was diagnosed in 61/1236 (4.9%) consecutive perinatal autopsies conducted between 1990 and 2002. Interestingly, a prior study from our institution, conceivably representing a population with similar demographics, found a strikingly similar prevalence (4.2%) of
GBS-positive autopsies between 1975 and 1982.
15
These numbers suggest that, in spite of improved diagnostic, prophylactic and therapeutic strategies, the rates of lethal perinatal GBS infection appear to have remained stable over the last decades.
In 58 of 61 GBS-positive cases, death was attributed solely to perinatal GBS infection, leading to the diagnosis of ‘fatal perinatal
GBS infection’. Fetal and placental tissue sections of these 58 preterm (<36 weeks) and term (
Z
36 weeks) stillborn fetuses and newborn infants were evaluated for the presence and severity of acute inflammation. The rate of acute chorioamnionitis of the placenta, characterized by neutrophilic infiltrates in the placental membranes and chorionic plate, was two-fold higher in preterm than in term fetuses/infants. Similarly, the rate of advanced inflammation of the umbilical cord, characterized by acute arteritis and inflammation of the perivascular Wharton’s jelly (funisitis), was almost three-fold higher in preterm fetuses/infants. Other studies, though different in study design and aims, have similarly recognized that placental inflammation tends to be more prevalent in preterm compared with term newborns with neonatal infection.
12
In addition to placental inflammation, we have studied the frequency of fetal inflammation in GBS-infected fetuses/newborns.
Pulmonary inflammation, defined as the presence of intra-alveolar neutrophils and/or true pneumonia, was present in 25/58 (43%) of fetuses/infants with GBS infection and occurred with similar frequency in preterm or term infants. Gastrointestinal neutrophils were identified in 15/43 (35%) of preterm fetuses/infants with GBS infection. Virtually all fetuses/infants with gastrointestinal neutrophils also had pulmonary neutrophils, indicating a possible common pathogenetic mechanism. Of interest, none of the term infants showed gastrointestinal neutrophils, although pulmonary neutrophils were seen in 5/15. Whether the lack of gastrointestinal neutrophils in infected term infants is due to more mature local immune responses, more rapid intestinal transit, or other factors, remains to be determined.
The different histologic inflammatory response to perinatal GBS infection in preterm and term fetuses/infants is strongly suggestive of age-specific interactions between microorganisms, host and placenta. Among the myriad of factors regulating the inflammatory reaction to an invading microorganism, maturation of the host immune system is likely the pivotal event implicated in the agespecific histologic inflammatory response. Of interest, levels of IL-6,
444 an inflammatory cytokine that is considered an important marker for neonatal infection, have been shown to be significantly different in preterm and term newborns in response to neonatal infection, attributed to immaturity of the preterm immune system.
8,12,16
Overall, the sensitivity of histopathologic analysis of fetus and placenta for the presence of neutrophilic infiltrates/acute inflammation (67% in preterm and 33% in term cases) was much lower than suggested in the current literature for neonatal infections in general.
17,18
Our findings are in sharp contrast with those of Korbage de Araujo et al.
17 who reported 100% sensitivity of histologic chorioamnionitis in preterm newborns considered infected based on various clinical criteria which led them to conclude that ‘‘histological chorioamnionitis is the most important risk factor for neonatal infection in premature newborns’’.
Smulian et al.
18 similarly stated: ‘when there is no placental histologic inflammation, it is reasonable to conclude that significant infectious causes of maternal or infant symptomatology are less likely’’. Contributing factors to the striking discrepancy between their findings and those presented in this study may include different demographics and different inflammatory response to GBS infection vs any putative ‘infectious organism’.
The low sensitivity of fetoplacental inflammation seen in our study has major clinical implications. Placental examination was negative in 1/3 preterm and in 2/3 term fetuses/infants with fatal
GBS infection. This high false-negative rate emphasizes the fact that the absence of acute chorioamnionitis on placental examination does not rule out serious infection in newborns with a concerning clinical presentation. The low sensitivity of acute chorioamnionitis as marker of fetal infection further underscores the importance of autopsy
F which routinely includes post-mortem lung and blood cultures
F in perinatal deaths, be they preterm or term.
In conclusion, we have determined the rate of histological fetoplacental inflammation in infants and fetuses with lethal perinatal GBS infection. Even in this most extreme form of perinatal GBS infection only 1/3 term and 2/3 preterm placentas showed evidence of inflammation, suggesting that less severe, nonlethal forms of GBS infection may even less frequently be associated with placental inflammation. This study was limited to
GBS infection, the most important bacterial cause of perinatal morbidity and mortality. The rate of histologic fetoplacental inflammation in association with other bacterial infections remains to be determined.
Acknowledgement
We thank Ms. Valerie Luks for helpful discussions and assistance in data collection.
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