Human Parvovirus (B19V) is a single stranded, non-enveloped DNA virus from the family
Parvoviridae, genus Erythrovirus 1 . Infection results in a flu-like illness, which may be asymptomatic in the host. It is the causative agent in erythema infectiosum (Fifth disease); a mild self-limiting disease that usually presents in childhood with a distinct facial rash:
‘slapped cheek syndrome’. Greater than 50% of the population has been infected by adulthood 1 .
Infection with B19 during pregnancy is mostly asymptomatic and causes no detrimental effects to the fetus; however in approximately 30% of cases vertical transmission takes place which increases morbidity and mortality to fetal outcome 3, . Fetal effects are increased if infection occurs within the first twenty-four weeks of gestation and include red blood cell destruction, decreased haematopoiesis, thrombocytopenia and fetal anaemia 4 .
Haematopoiesis is augmented during this critical period to meet the demands of the growing fetus therefore any insult can pose the most detriment 3 . In severe cases, anaemia can lead to non-immune hydrops fetalis (NIFH) (Figure 1) (Figure 2), cardiomegaly, pericardial effusion, intrauterine death (IUD) or stillbirth 2,3,5,7 (Table 1). Hydrops fetalis develops secondary to bone marrow aplasia and is detected on ultrasound scan (USS) 3,5 (Figure 1).
Consequences of Fetal Anaemia in Pregnancy
Low haemoglobin
Thrombocytopenia
Ascites
Heart failure
Hydrops fetalis
Cardiomegaly
Death (intrauterine/ neonatal)
Table 1. The consequences B19V induced fetal
anaemia.
Figure 1. Ultrasound scan showing a transverse view of the abdomen with an accumulation of fluid resulting in ascites.
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Figure 2. A schematic diagram illustrating the common potential causes of hydrops fetalis. B19V infection is categorised as a non- immune cause.
Pathogenesis
B19 virus exhibits tissue tropism for fetal erythroid progenitor cells found in the liver, bone marrow, umbilical cord and peripheral blood via the cellular globoside receptor (blood group
P antigen) that is present on haematopoietic percursors, endothelial cells, fetal myocytes and placental trophoblast 3,4 . Recent studies have shown an inhibitory effect on megakaryocyte progenitor cells colony forming ability in situ by the viral B19 antigen NS1 .
Reduction of bone marrow cells will lead to anaemia which in turn may lead to further complications such as hydrops fetalis, thrombocytopenia and death 2 . Fetal anaemia can be defined as a state where there is a decrease in the number of erythrocytes, therefore haemoglobin within fetal circulation. This results in an inability to meet the oxygen demands of growing tissues, leading to hypoxia and cell death. Anaemia is categorised as mild, moderate or severe depending on the haematocrit* (Table 2).
Haematocrit (%)
Mild 30 - 40%
Moderate 15 – 29%
Severe <15%
Table 2. Categorisation of anaemia determined by haematocrit (Packed cell volume).
* Haematocrit is the percentage volume of red blood cells in blood. Normal levels are approximately 40% and independent of body size.
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Diagnosis
Extent of anaemia must be determined in order to direct treatment. Diagnosis can occur via invasive or non-invasive techniques. The latter must be available to diagnose the pregnancies most at risk, thus minimising complications from fetal sampling by avoiding an associated procedure related pregnancy loss (PRPL). Mild anaemia is unlikely to require intrauterine therapy (IUT) unless significant associated complication.
Treatment
Fetal B19 infection is treated by IUT which permits resolution of anaemia and associated complications. It enables the fetus to meet oxygen demands for development whilst recovering from the infection. This can occur within a gestation where delivery is not an option and an IUT can be a rescue procedure that permits eventual delivery of live infant.
Adult haemoglobin has a lower affinity for oxygen however without transfusion the prognosis is poor. Perinatal survival following IUT in B19 infected fetuses has been reported to be in the region of 67%-85%; as opposed to greater than 90% in red cell alloimmunisation affected pregnancies 3 . Higher mortality rate in the B19 population may be due to complications from haematopoietic arrest at a critical stage which the fetus is unable to recover from. Thrombocytopenia is a prominent feature in B19 fetal infection therefore treatment induced exsanguination is a further complication 5 . Transfusion method and addition of platelets may reduce this risk. In comparison to alloimmunised pregnancies where serial IUTs are required until birth, B19 pregnancies often require a single IUT in order to improve 5 .
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The Ian Donald Fetal Medicine unit is situated within the maternity building of the Southern
General Hospital, Glasgow and is the national centre for intrauterine transfusions (IUT).
Referrals are received from Scotland, Northern Ireland and Iceland.
Data collection
This project was a retrospective analysis of data from all pregnancies that underwent IUT for
B19V infection. Data collection contained both clinical information and laboratory blood results from proven B19V infection from 2008 - 2013. A total of twenty –nine women were seen at the unit. Twenty-eight patients underwent thirtyeight IUT’s. From this cohort maternal parameters were recorded: maternal age, gestational age at IUT, pre/ post IUT blood sampling, complications (Table 3) and fetal outcome.
Fetal investigations
Ultrasound (USS)
Fetal anaemia secondary to B19V was diagnosed via middle cerebral artery Doppler analysis. Identification of moderate to severe anaemia can be detected with 100% sensitivity and 12% false positive rate. The cut-off used for peak systolic velocity was 1.5 multiples of the median (MoM) for gestational age.
Fetal blood sampling
Positioning of the fetus (cord access) and gestation indicated whether pre –IUT sampling was possible. Gestations less than twenty weeks were not sampled prior to procedure. A needle was inserted into the umbilical cord to gain intravascular access to fetal circulation.
Once a sample was successfully obtained it was analysed to determine the pre-IUT haematocrit (Hct), mean cell volume (MCV) and red blood cells (RBC).
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Complications Arising from Intrauterine Transfusion
Cord haematoma
Fetal bradycardia
Exsanguination from puncture site
Fetomaternal haemorrhage
Intrauterine infection Maternal alloimmunisation
Pre-term delivery Fetal death
Table 3. Procedure related complications for intrauterine transfusions.
TOTAL RESULTS
Twenty nine women with confirmed Parvovirus (B19) infection were treated at the Ian
Donald Fetal Medicine Unit. B19 infection was diagnosed and confirmed by serology and
PCR. Twenty –eight (96.6%) of women underwent thirty–eight IUT’s between the years 2008
- 2013. One (3.4%) procedure was abandoned as a concealed placental abruption was discovered during USS. An IUT was not undertaken on this occasion due to the intrauterine death (IUD). This has been excluded from the data. The mean maternal age was twentyeight years (16 – 39 years). Mean gestational age at IUT was 22 weeks (18-28 weeks).
Ultrasound investigation prior to IUT showed all cases to have fetal anaemia based on MCA-
PSV > 1.5 MoM. From available data twenty-one (75%) of those that underwent IUT had hydrops fetalis.
Total Pregnancy Outcome
Seven (25%) of the fetuses died in utero following IUT; Four (14.3%) of this group died within one week of the procedure. Six (21.4%) live births were recorded. A total of twelve
(42.9%) patients were discharged from the centre due to resolving infection and returned to their original health board. Fetal outcome for these patients is unknown. One patient (3.6%) underwent medical termination of pregnancy (MTOP) and one patient (3.6%) is still undergoing treatment for ongoing infection and fetal anaemia. There was one (3.6%) neonatal death (Table 4) (Figure 3).
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Pregnancy outcome Patient number Gestation Range at
Presentation
Live birth
IUD
Discharged
Termination
Ongoing treatment
Neonatal death
1
1
6
7
12
1
(20-28)
(18-24)
(18-28)
(21)
(18)
(20)
Table 4. Pregnancy outcome for all maternities presenting with confirmed B19V infection for treatment to the Ian Donald Fetal Medicine unit.
Figure 3. Pregnancy outcome for all confirmed B19 infection between the years 2008-2013.
SUB-COHORT
Pregnancy outcome depending on procedure route
Intrauterine transfusion (IUT) was performed via three different routes in the B19 cohort
(table 5).
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LIVE
IUD
DISCHARGED
NND
MTOP
ONGOING
TREATMENT
Intravenous (IV)
1
2
4
-
-
-
Table 5.
Pregnancy outcome depending on IUT route.
Pregnancy outcome with associated complications
Hydrops fetalis
Intrahepatic (IH)
5
3
7
-
1
1
Intraperitoneal (IP)
-
2
1
1
-
-
From the available data twenty-one (75%) of the fetuses that underwent IUT had confirmed hydrops fetalis (data missing from seven). (Table 6) (Figure 4).
LIVE BIRTH
IUD
DISCHARGED
TERMINATION
ONGOING TREATMENT
PREGNANCY OUTCOME – HYDROPS FETALIS
6
5
8
1
1
Table 6. Pregnancy outcome for all maternities that had hydrops fetalis associated with fetal anaemia due to congenital B19 infection.
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Figure 4. Pregnancy outcome for all maternities that had hydrops fetalis as a complication of B19 infection.
Haematological complications
Fetal blood sampling was obtained in twenty (71%) cases. From this the haematocrit and platelet levels determined fetal anaemia and whether thrombocytopenia thus determining treatment method.
Anaemia
Anaemia levels were determined via haematocrit and categorized into mild, moderate or severe (Table 7.1).
MILD
MODERATE
LIVE
1
1
IUD
1
1
DISCHARGED
4
1
NND
-
-
ONGOING
-
-
SEVERE 3 4 2 1 1
Table 7.1. Tabulated representation of the degree of anaemia detected via blood sampling within the sub group of twenty maternities that had laboratory results and their associated pregnancy outcome.
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Thrombocytopenia
Pre – IUT blood sampling in the twenty recorded (Table 7.2) (Figure 5.1). Platelet levels were observed in a control cohort of pregnancies undergoing IUT for alloimmunisation. The platelet levels between the B19 cases were then compared to the alloimmunised cases
(Figure 5.2)
PREGNANCY OUTCOME THROMBOCYTOPENIA
LIVE BIRTH
IUD
DISCHARGED
ONGOING TREATMENT
6
1
5
4
NEONATAL DEATH 1
Table 7.2. Pregnancy outcome for all maternities that had associated thrombocytopenia with fetal anaemia due to congenital B19 infection.
Figure 5.1. Pregnancy outcome for all maternities that had thrombocytopenia as a complication of B19 infection.
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Alloimmunised control cohort
A cohort of twenty-eight alloimmunised patients were selected as a control group to enable comparisons to be made when assessing platelet counts in B19 anaemia. Data from the initial IUT was compared with initial IUT for B19. Maternal parameters were matched. Mean age was 29 years (range 24-36 years) and mean gestation was 24 weeks (18-30 weeks).
Platelet counts were obtained from laboratory data from the initial IUT. Haematocrit and platelet counts were plotted on a graph and compared to B19 maternities (Figure 5.2). By comparing B19 anaemia to gestation matched alloimmunised anaemia, it is possible to identify whether this association is specific to B19 infection or if present in all fetal anaemia
50
40
30
20
10
0
0 100 200
Platelets (10x 9 )
300 400 despite the underlying cause.
A. B.
Figure 5.2. Platelet counts were plotted against haematocrit in order to determine the correlation between haemoglobin (hb) levels and thrombocytopenia. A. Fetal anaemia induced by rhesus disease displays a greater platelet level range (0-400). Anaemia in this cohort is mostly mild-moderate. B. Platelet range is smaller than in
Rhesus anaemia (0-150). There is a greater degree of thrombocytopenia in all cases. Most cases have both severe anaemia and severe thrombocytopenia.
In this cohort of pregnancies that presented with confirmed Parvovirus B19 infection in the last five years, it was found that fetal outcome depended on various factors. These include gestation at transmission, levels of anaemia at presentation, severity of thrombocytopenia and treatment route for IUT. Twenty-nine women in total had B19 infection between the years 2008-2013. One pregnancy is still undergoing treatment at the time of completing this study. From this cohort, one pregnancy ended prior to treatment as USS revealed the
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presence of a grossly hydropic fetus and an intrauterine mass which was suggestive of a
“concealed placental abruption”. The most likely outcome following parvovirus B19 infection was discharge from the unit (42.9%). These maternities returned to their own health boards and fetal outcome information was therefore unavailable. The fact that they were discharged suggests that they had improved. Live births were recorded in 21.4% of cases. All of which were greater than 20 weeks gestation at presentation (range 20-28 weeks). Intrauterine deaths (IUD) were record in 25% of cases; with fetal demise occurring in 43% of this subcohort within one day of IUT. A further 14% died within one week of the procedure. Whether the procedure contributed to these deaths is unknown. Gestation range for IUD was 18 -24 weeks. Pregnancies less than twenty weeks gestation required an intraperitoneal (IP) exchange method rather than direct vascular access. This method resulted in slower resolution of fetal anemia however it is the only means available to transfuse to smaller fetuses when vascular access is not possible. It is reserved for ‘small sick fetuses’ and this may suggest why no live births were recorded. It was used in only 14% of cases, which may be affecting the true morbidity/ mortality rate. Favoured transfusion access was intrahepatically (IH). This reduced the risk of exsanguination in the severely thrombocytopenic. If bleeding from the puncture site does occur, then blood can be reabsorbed into the circulation and is not lost into the amniotic fluid. This method of IUT had the highest success rate with 29% live born and 41% discharged from the unit as B19 infection was resolving. IUD rate for this method was 14%.
Hydrops fetalis was documented in 75% of cases. Information was missing from the other
25%. This does not indicate that hydrops was absent but that it was not evident from the available data. The presence of hydrops did not adversely affect fetal outcome. Outcome was dependent on haemoglobin. Low haematocrit was a measure of anaemia and directly related to morbidity. Mortality rate was four times greater for those with severe than those with mild anaemia. Thrombocytopenia was another associated morbidity factor. All the B19 fetuses had a degree of thrombocytopenia ranging from mild to severe. Platelet levels were categorised as severely affected in 85% of cases. This made treatment more complicated as there is an increased risk of exsanguination thus stress the already hypoxic cardiac myocytes and lead to heart failure. It was noted that B19 caused the fetus profound anaemia and induced thrombocytopenia in every case. If detected early and correction of anaemia occurred promptly, then usually one IUT is all that was required.
Using a cohort undergoing IUT for alloimmunisation for comparison then it was possible to determine if thrombocytopenia was a consequence of all fetal anaemia despite the underlying mechanism. Haematocrit levels revealed that anaemia was less than that in the
B19 cohort. This suggests that there may be less of a rapid red cell loss with anaemia
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developing gradually and with possibly fewer complications. Thrombocytopenia is less of a factor than that noted in the B19 fetuses. Only 21% had severe thrombocytopenia and 39% had none. This may be due to the lytic element of rhesus disease affecting primarily the red cell, whereas in B19 infection arrest of early erythroid precursors occurs resulting in decreased synthesis of various lineages. The difference in the mechanism of how anaemia evolves should identify how platelet levels are more affected in B19 infection than alloimmunisation.
In conclusion, infection with Parvovirus B19 during pregnancy can be vertically transmitted to in 30% of cases. Although mild and self-limiting for the mother, there can be significant morbidity and mortality to the fetus. Any suspicion of potential infection should be diagnosed and referred promptly for further investigation to minimise the potential of an adverse fetal outcome. As B19 related anaemia causes arrest in erythroid lineage then a profound decrease in both red cell and platelets are evident in the fetus. This can further increase the risk of complication from potential lifesaving IUT treatment via exsanguination. Due to this, all presenting maternities with B19 infection should be treated with IP or IH IUT to decrease bleeding risk and enable the fetus to recover. No IV cord transfusions should be undertaken in these fetuses as all will have a degree of thrombocytopenia. This will undoubtedly prevent further blood loss and may serve to decrease mortality in this already at risk population.
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6 th November 2013)
2. De Jong EP, Lindenburg IT, Van Klink JM, Oepke D, Van Kamp IL, Walther FJ, Lopriore
EL. Intrauterine transfusion for parvovirus B19 infection: long term neurodevelopment outcome, American Journal of Obstetrics and Gynaecology 2012; 206 (204): 1-5
3. Brennand J, Cameron A, Fetal disease: Pathogenesis and Principles. Red cell alloimmunisation In: Kilby M, Oepkes D, Johnson A (eds) , Fetal therapy , Cambridge,
Cambridge university press, 2013
4. De Haan TR, Van den Akker ESA, Porcelijn L, Oepkes D, Kroes ACM, Walther FJ.
Thrombocytopenia in hydropic fetuses with parvovirus B19 infection: incidence, treatment and correlation with fetal B19 viral load, BJOG 2008 ; 115: 76-81
5. Fairley CK, Smoleniec JS, Caul OE, Miller E. Observational study of effect of intrauterine transfusions on outcome of fetal hydrops after parvovirus B19 infection, The Lancet 1995;
346: 1335-37
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