in 2008 , a 30-year - old primigravida physician experienced intrauterine fetal demise ( iufd ) at 20 weeks gestation , as established by last menstrual period and confirmed by ultrasound at 8 weeks .
the patient spent most of her pregnancy providing direct patient care . in october 2007 , during gestational weeks 26 , she was exposed to at least 2 patients with presumed influenza .
she reported symptoms of fever , myalgia , headache , and cough during gestational week 4 .
she had no testing for influenza , did not receive antiviral therapy , and took acetaminophen ; her symptoms resolved .
an ultrasound at 18 weeks demonstrated early growth restriction and oligohydramnios with normal appearing fetal kidneys and head .
the patient had an unremarkable medical history , did not smoke , and was normotensive throughout pregnancy .
microscopically , histiocytes were abundant in the maternal space ( chronic intervillositis ) and were noted within the fetal chorionic villi ( hofbauer cells ; figure 1 , panel a ) .
histologic analysis of fetal autopsy specimens showed scattered luminal histiocytes of the lung and gut .
no other inflammatory changes or viral inclusions were identified in the placenta or fetal organs .
tissue sample from 30-year - old primigravida patient exposed to seasonal influenza ( h1n1 ) .
a ) intervillous ( maternal ) spaces with clusters / sheets of histiocytes ( chronic intervillositis ) and fibrotic fetal chorionic villi with hofbauer cells  histiocytic inflammation ( hematoxylin and eosin stain , original magnification 200 ) .
b ) dual - stained immunofluorescent assay showing antibodies to influenza a virus ( h1n1 ) ( tetramethylrhodamine isothiocyanate , red ) and cytokeratin ( fluorescein isothiocyanate , green ) in intravillous ( fetal ) and intervillous ( maternal ) space .
chronic intervillositis was evident in the placental histology and has been previously described with nonspecific changes in miscarriage and recurrent pregnancy loss ( 4 ) .
histiocytes identified from the maternal intervillous space and fetal chorionic villi demonstrated characteristics of viral production ( figure 2 ) .
several well - formed viral capsids were noted within the cytoplasm , each containing regularly spaced projections along the surface of the virion corresponding to the hemagglutinin and neuraminidase spikes .
tissue sample from 30-year - old primigravida patient exposed to seasonal influenza ( h1n1 ) .
electron microscopy ( original magnification 70,000 ) of maternal intervillous space and fetal chorionic villi , showing intranuclear viral transcription aligning along the nuclear envelope 
electron hypodensities ( asterisks ) , and intracytoplasmic viral production in varying stages shown by numerous electron densities ( v and ^ ) .
pcr for m1 capsid protein confirmed influenza a. immunohistochemical testing was performed on tissue from the placenta and on a sampling of fetal organs by using influenza a virus ( h1n1)specific antibody . in the placenta , stippled immunofluorescence ( figure 1 , panel b )
was noted in the histiocytes of the intervillous space ( maternal ) and fetal intravillous histiocytes . in the fetal organs ,
immunofluorescence for subtype h1n1 was notable in the surface epithelial cells and scattered luminal histiocytes of the fetal respiratory and gastrointestinal tracts .
no immunofluorescence was noted within the fetal organs , which implied transamnionic passage of virus ( amnionic fluid infection ) .
y - specific immunofluorescent stain with histiocyte counterstaining was performed . because only the intravillous ( fetal ) histiocytes stained positively , maternal and fetal inflammatory responses were confirmed .
harris reported higher rates of miscarriage after exposure and infection in the earliest months of pregnancy in the spanish influenza outbreak of 1918 ( subtype h1n1 ) ( 5 ) .
hardy et al . reported a similar observation following the asian influenza outbreak of 195758 ( 6 ) , as did investigators in the united kingdom during the 198586 influenza season ( 7 ) .
yawn et al . documented influenza a transplacental transfer from the mother to amniotic fluid and fetal heart ( 8) .
. summarized placental findings associated with influenza infections in publications from 1987 and 1994 , describing perivillous and villous inflammation with concurrent amniotic fluid immunofluorescence for influenza virus ( 9 ) . in another study ( 10 ) , researchers from beijing , people s republic of china , reported autopsy findings for 2 patients ( 1 of whom was 4 months pregnant ) who died of avian influenza a ( h5n1 ) .
viral antigens were present in the maternal pulmonary system , and virus was detected in placental hofbauer cells ( histiocytes ) , cytotrophoblast , fetal lung , circulating mononuclear cells , and liver macrophages ( 10 ) .
their documentation of tropism of the influenza virus to placental tissue is similar to the histopathologic features in our report .
our unexpected discovery of viral production in placental , maternal , and fetal histiocytes is another example of transplacental passage of influenza .
adverse fetal outcomes have reportedly included congenital malformation and schizophrenia , but factors that determine these effects remain unclear ( 11,12 ) .
fetal consequences of influenza exposure may be an effect of systemic inflammatory response to the infection , which could represent direct action of the virus on the placenta , the maternal  fetal interface , or the fetus .
reported the inflammatory response of decidual and fetal tissue in the presence of influenza virus infection and demonstrated expression of mrna for a set of proinflammatory cytokines such as interleukin-6 , tumor necrosis factor- , and granulocyte  macrophage colony - stimulating factor , secreted in substantial amounts in response to exposure to influenza virus in vitro ( 13 ) .
as our case suggests , a complex interaction of maternal and fetal responses at the interface is a more likely explanation .
a total of 15%20% of pregnancies end in spontaneous miscarriage , most before gestational week 12 ( 3 ) . approximately 50% of miscarriages are associated with chromosomal defects , which leaves many other miscarriages unexplained ( 14 ) .
examined first trimester miscarriages not associated with chromosomal abnormality , observing histologic changes of chronic intervillositis and increased perivillous fibrin ( 15 ) .
the mechanism of loss was thought to be related to a maternal inflammatory response to infectious antigen or an autoimmune phenomenon . whether these findings can be extrapolated to second trimester losses
histopathologic features of these early second trimester miscarriages are not well studied , and descriptions are usually included in reports of fetal losses during 1427 weeks , which include iufd ( > 20 weeks ) and miscarriage .
consequently , a direct causal relationship between influenza a and fetal demise has not been well established . in our report , a retrospective investigation of the patient s products of conception with ultrastructural , immunohistochemical , and molecular methods that identified subtype h1n1 implies an exposure during her first trimester .
type - specific serologic analysis was not possible because she received influenza vaccine several weeks after presumed exposure .
the maternal and fetal inflammatory responses ( chronic intervillositis ) after placental infection may have reduced villous surface area for oxygen and nutrient transport , resulting in growth restriction and ultimately second trimester loss .
investigation of the effects of influenza in early pregnancy is needed to evaluate potential pathophysiological relationships between maternal exposure , infection , and fetal loss or adverse outcome . during the 200910 influenza pandemic ,
the centers for disease control and prevention ( atlanta , ga , usa ) collected information from populations exposed to and infected with pandemic ( h1n1 ) 2009 virus .
we recommend that future influenza outbreak evaluations of women exposed to influenza with first or early second trimester pregnancy loss include collections of placental and fetal tissue samples .
 a second trimester fetal demise followed influenza - like illness in early pregnancy . 
 influenza a virus ( h1n1 ) was identified in maternal and fetal tissue , confirming transplacental passage . 
 these findings suggested a causal relationship between early exposure and fetal demise . 
 management of future influenza outbreaks should include evaluation of products of conception associated with fetal loss . 
The Case
Conclusions