Material and Method:Placentae from 41 cases of otherwise uncomplicated antenatal and intranatal pregnancies with meconium stained liquor at 37 completed weeks of gestation were studied, both grossly and microscopically, comparing them with controls of 41 cases of clear liquor. Apgar score of all newborns at 1 minute and 5 minutes were recorded and correlated with histopathological findings.
Results: Both cases and controls were found to be age matched. Meconium stained liquor was associated with more caesarian section than the clear ones. Significant correlation was found with meconium stained liquor and low Apgar scores. Histopathology of placenta revealed many statistically significant associations between specific placental histopathology in meconium stained liquor and depressed Apgar score. Evidence of placental vasculopathy rather than meconium induced placental damage came out as the potential culprit in causing a low Apgar score in this case control study.
Conclusion: Placental vascular changes have a role in meconium staining of liquor. If timely interventions are taken, the chance of development of fetal distress is low.
Fetal distress is assessed by the Apgar score (less than 7 at 1 minute and 5 minutes), cardiotocograph traces, and cord or fetal scalp blood pH (less than 7.2) etc. Among these, Apgar score assessment is simple and commonly employed Meconium passage has been significantly associated with low Apgar scores, cord blood pH of 7.0 or less, respiratory distress, seizures in the first 24 hours, and the need for delivery room resuscitation. Neonatal morbidity of all kinds has been significantly associated with meconium stained amniotic fluid as compared to clear amniotic fluid [1,2]. Meconium staining of the liquor may be the thin or thick type. Thick meconium is associated with higher morbidity and mortality in comparison to clear liquor [3-5]. It is also associated with a higher incidence of emergency caesarean delivery [4,6,7].
Meconium aspiration syndrome is a life-threatening respiratory disease in infants born through meconium stained amniotic fluid. It is associated with thick meconium, low Apgar score and non-reassuring fetal heart rate tracing [3,8]. There is some evidence that meconium may interfere with surfactant production and in high enough concentrations, have a direct toxic effect on type II pneumocytes, possibly contributing to the meconium aspiration syndrome [9]. All cases of meconium stained liquor and especially the thick meconium type should therefore be continuously monitored to prevent serious complications [4].
Meconium is thought to cause placental and umbilical cord vasoconstriction along with cerebral and fetal hypoperfusion. These may be the causes for a major poor outcome in meconium stained liquor [10,11]. Meconium stained liquor is associated with an increased frequency of chorio-amnionitis [12].
It is not clear that whether meconium staining of liquor is associated with demonstrable placental pathology which may give rise to fetal distress, either directly or indirectly, or whether placental pathology gives rise to meconium staining and in turn causes fetal distress. It is not discernible which is the primary event among these variables.
There are many questions regarding the cause, effect, clinical significance and pathologic expression of in-utero meconium passage which are, as yet, unresolved. In the majority of infants, meconium passage is a reflection of physiological immaturity, although in some, it appears to be associated with adverse stimuli, out of which fetal distress is a significant factor.
It has also been observed that intra-uterine fetal distress is the consequence of maternal and fetal vascular compromise, though the normal placenta has considerable functional reserve. Placental infarct associated with crowding ghost-like villi, fetal thrombotic vasculopathy, intra-villous and peri-villous fibrinoid, placental villous hypoplasia associated with increased inter-villous spaces and exaggerated syncytial knots are some of the pathologic findings associated with fetal and maternal vascular compromise.
It is not certain that such factors, to what extent, are associated with fetal distress and thereby act as potential causes behind the meconium passage in-utero.
There are many studies which describe meconium induced fetal distress. A few studies have described placental changes in meconium stained liquor. However, there are lack of studies describing correlation of placental histopathology with fetal distress in meconium stained liquor.
This study has been undertaken to determine the association between meconium stained liquor with fetal distress and specific placental pathology in such cases. For this purpose, macroscopic and microscopic changes of placentae associated with meconium stained liquor were compared with those in clear liquor in otherwise uncomplicated term pregnancy.
The information collected were history & clinical examination (of the mothers in labour), observation (in the labour room), record review (antenatal card, bed head ticket) and recorded histopathological findings of the placentae.
The parameters were degree of meconium staining (light/ deep), Apgar scores of the newborns, and histopathological changes in placentae of the cases and controls.
After approval from the ethical committee, we attended the labour observation room of Gynaecology & Obstetrics Dept. of Burdwan Medical College. After duly filling up the consent and case record form (history and clinical examination), inspection of the pregnant mother in term gestation with meconium stained liquor took place and the time of rupture of membrane was noted. Mode of delivery of the case was decided by the obstetricians and delivery was done either by vaginal delivery or caesarean section. We collected the placenta in 10% buffered formalin solution. Apgar scores of the baby at 1 minute and 5 minutes were recorded. Thus we collected 41 placentae from thin or thick meconium stained liquor cases as per availability of such cases.
We collected 41 placentae with clear liquor after vaginal delivery from age matched control mothers without any antenatal and intranatal complication. We also noted Apgar scores of those newborns at 1 minute and 5 minutes.
Apgar score was determined by noting i) color, ii) respiratory effort, iii) heart rate, iv) muscle tone and v) reflex irritability. Each variable scores 2 points. The cumulative score (maximum being 10 and minimum being 0) was graded as follows: No depression (score 7- 10); mild depression (score 4- 6); and severe depression (score 0- 3)
The color of liquor was graded as- 0 (Clear), 1 (Thin), and 2 (Thick)
After getting the placentae, gross examinations and procedures were performed; sections were taken from different parts of the fixed placentae after one day and again the sections were fixed in neutral buffered 10% formalin. Paraffin blocks were prepared after following the routine histopathological techniques. Staining of sections (5μ thick) was done with routine Haematoxylin & Eosin stain. Light microscopic examination was done and results were noted. Different gross and histopathological changes were recorded in the histopathological data record form. They were corroborated with the respective Apgar score to uncover any relationship between them.
Examination of Placenta
I. Macroscopic examination
Each placenta was examined meticulously as early as
possible after collection following delivery and the findings
were noted in the case record form. Photographs of the
specimen were taken accordingly. The specimen was then
placed in 10% neutral buffered formalin for fixation.
The specimen was examined macroscopically for the following parameters (13):
The size of the placental disc and umbilical cord, shape, weight, colour, fetal surface membrane (graded as 0,1 and 2 according to the intensity of meconium staining), maternal surface, surface vessels and cut surface of the disc and cord.
II. Microscopic examination
Seven sections (14,15) were taken for histopathology of
placenta including three sections from the disc including
fetal and maternal surface, two sections from the fetal
membrane (jelly roll technique) and two sections from the
umbilical cord.0
Microscopically, the following parameters were noted.
1. Intervillous space (IVS): It is graded as 0 (narrow IVS),
1(normal) and 2 (widened IVS )
2. Intravillous fibrinoid and perivillous fibrinoid: In this
study, both are graded as 1 (normal), 2 (mild increase) and
3 (marked increase).
3. Villitis: It is graded as 0 (absent) and 1(present).
4. Syncytial knots (SK): It is increased at term as well as in
hypoxic conditions. It is graded as 1 (up to 5 SK/villous in
the majority of the villi), 2 (5- 10 SK/villous in majority of
the villi) and 3 (>10 SK/ villous in the majority of the villi).
5. Calcification: Focal calcification is considered normal at term, but excessive calcification may have underlying pathology. In this study it is graded as 0 (no or focal calcification) and 1 (marked calcification).
6. Infarction: Infarcts are the result of circulatory
disturbances. In this study it is graded as 0 (absent) and 1
(present).
7. Fibrosis: Villous stromal fibrosis may occur in hypoxic
conditions. It is graded as 0 (absent) and 1 (present).
8. Blood vessel changes: There may be thrombosis/ avascular villi/ atrophy of villi/ fetal thrombotic vasculopathy. In the present study, blood vessel changes are graded as follows: 0 (no change); 1 (mild changes (focal); 2 (marked changes (global)
9. Chorion and amnion: Multilayering of amniotic membrane, ballooning degeneration, necrosis and chorioamnionitis may be present in various proportions in meconium staining. The changes are graded as 0 (absent/ no change) and 1 (present).
10. Umbilical cord: There may be funisitis (inflammation of cord) or cord vasculitis. Changes are graded as 0 (absent) and 1 (present).
11. Chorangiosis : It may be an incidental finding. It is considered when there is presence of more than 10 terminal villi with more than 10 capillaries (actually more than 15 are usually present) involving several areas of placenta. It may be due to abnormal maturation of villi and hypoxia.
At the end of the study, all the data was compiled and tabulated. Analysis was done by using suitable statistical methods (2-tailed t-test and Pearson Chi-square test) and appropriate software (SPSS v.20).
The mean birth weight of babies of cases was 2818.90g. and of the controls was 2679.88g. The difference was statistically significant. Higher birth weight was associated with meconium staining of liquor in comparison to clear liquor.
The meconium stained placenta and placenta with clear meconium was grossly evident (Figure 1,2).
Figure 2: Gross photograph of a meconium stained placenta with opaque, gray-brown fetal surface.
The mean placental weight of cases was 480.98 g. and of controls was 487.32g. The difference was statistically significant. So, here it was evident that lower weight of placenta was associated with occurrence of meconium staining of liquor (Table I, Figure 3). In this study there was no abnormality noted in maternal surface or cut surface of placenta in either case or control group. No abnormality was seen in gross and microscopical examination of umbilical cord. Among the meconium stained liquor group, 19.6% (8/41) cases had thin and 80.4 % (33/41) cases had thick meconium stained liquor. There was increased incidence of caesarean section in meconium stained liquor group. 29.3% (12/41) newborns were delivered vaginally and 70.3% (29/41) babies were born through caesarean section.
Salient microscopical findings in this study as observed from different tables and statistical analysis were increase in inter-villous space (19.5%), prominence of intra- (19.5%) and peri-villous fibrinoid (24.4%) (Table II), exaggerated syncytial knots (26.8%), obvious blood vessel changes (31.7%), calcification (intra- and peri-villous as well as within vessel wall) (13.4%) (Table III), villous fibrosis (7.3%), epithelial hyperplasia in amnion (39%), evidence of chorio-amnionitis (13.4%) (Table IV, V). The statistical significance in distinguishing placental changes from normal control was evaluated (Figure 4-9).
Table II: Evaluation of intervilllous space, intervilllous fibrinoid and perivillous fibrinoid.
Table III: Depicting incidence of villitis, exaggerated syncytial knots and villous calcification.
Figure 5: The increase in inter-villous space with perivillous fibrinoid (H&E; x100).
Figure 6: Intra-villous fibrinoid with calcification (H&E; x100).
Figure 7: Extensive perivillous fibrinoid in meconium stained liquor (H&E; x100).
Figure 8: Exaggerated syncitial knots in meconium stained liquor (H&E; x400).
Figure 9: Fibromuscular sclerosis with intravascular fibrin thrombi (H&E; x100).
Villitis (6.1%) and infarction (1.2%) were observed in this study in variable proportions but not statistically significant.
Villous chorangiosis, a peculiar finding in this study, which was present in 13.4% of cases, was not statistically significant as it is also observed in control normal placentas (Table V) (Figure 10).
Figure 10: Villous chorangiosis in a control placenta (H&E; x400).
Unlike in previous studies, there was no obvious change in the umbilical cord and rarely meconium laden macrophages in amnion were found in this study.
The Apgar score at 1 minute was as follows: 17.1% (7/41) were not depressed, even they were associated with meconium stained liquor. Mild depression was present in 60.5% (25/41) and severe depression was noted in 22% (9/41) of cases. Apgar score at 5 minutes after delivery room resuscitation was as follows: No obvious depression in 73.2% (30/41), mild depression in 24.4% (10/41) and severe depression in only 2.4% (1/41) of cases. A significant association was seen between green colored placenta (meconium) and mild depression of Apgar score (p-value <0.05) (statistically significant), when a comparative study was done between the Apgar score and color of the placentas. A widened inter-villous space was significantly associated with mild to severe depression, both at 1 minute and 5 min (p-value < 0.01), which was not observed in control cases. Persistent neonatal depression was significantly associated with an increase in the amount of intra-villous and perivillous fibrinoid in the meconium stained liquor group (p- value <0.002).
No significant association was found with presence or absence of villitis, in meconium stained liquor and neonatal depression, evaluated by Apgar score. (p- value >0.094). Exaggerated syncytial knots (Figure 8), though a feature of post-maturity, were also observed in hypoxic state, as revealed from above analysis, showing p-value <0.05 , which is statistically significant. Wide areas of heterotrophic calcification may be the end result of villous atrophy and fibrosis, leading to maternal and fetal hypoperfusion, is significantly associated in cases of meconium-stained liquor and associated neonatal depression (p- value <0.05 which is statistically significant). Blood vessel changes were a noticeable finding, in this study population (Cases=41), with a significant association with both 1 min. and 5 min. Apgar score (p- value <0.05; which is also statistically significant).
Fibro-muscular sclerosis with vascular obstruction (46.3%) (Figure 9) was seen in a substantial population of cases (19/41), which was statistically significant (p-value<0.05) finding (Table VI). We have observed that mild to severe depression were always associated with meconium stained liquor. Though this figure is statistically significant (Pearsons Chi- square test), but actually we had selected our controls as normal placenta at birth in an otherwise normal vaginal delivery. So, this finding is not significant in respect to our study population.
The mean age of the mothers in this study is 23.11 years (23.17 in the meconium group and 23.05 in the clear liquor group). There is no significant difference in the mean age between case and control population (by 2 tailed significance test the value is 0.805). In this study, 46.3% of the mothers in the meconium stained liquor group (19/41) and 43.9% (18/41) of the mothers in the clear liquor group were primipara. So, there is similarity of parity between cases and controls. However, Osava et al. [17] found higher incidence of meconium stained liquor in primipara in comparison to clear liquor cases in their study. Klufio et al. [18] found positive significant association between grand multiparty and meconium stained liquor. In the present study, mean and most frequently occurring gestational age in both meconium and clear liquor group is 37 weeks and the average birth weight (BW) of babies is 2749.39 g.. The mean BW in meconium group was 2818.90 g. and in clear liquor group it is 2679.88 g.. So, the BW is little higher in meconium group, having no statistical significance. However, Zhu et al. [20] noted in their study that birth weight was higher in meconium stained amniotic fluid group than that in clear amniotic fluid group (P < 0.001). However, Khazardoost et al.. [8] found that neonatal birth weight was lower in the meconium stained liquor cases. Odongo et al. [21], however, found no significant difference in the mean birth weights of the infants born to women in 36 meconium stained liquor cases and 41 clear liquor cases (3359.72 g. and 3260.24 g. respectively, p-value: 0.282). This study also showed similar results on statistical analysis. In the present study, the mean placental weight of the case population was 480.98 g. and of the control population is 487.32 g. In this study, we found 19.6% thin meconium liquor and 80.4 % thick meconium liquor among the cases. Meconium stained liquor is associated with increased incidence of caesarean section, as noted in the studies by Arulkumaran et al. [4], Shaikh et al. [6], Osava et al. .[17], Odongo et al.[21], Khatree et al. [22], and Klufio et al. [18]. Similarly, in the present study, there is increased caesarean section rate among meconium stained liquor group: 29.3% delivered vaginally and 70.7% delivered by caesarean section. But, in contrast, in a study by Kumari et al. [7] 60% patients delivered through normal vaginal delivery and 40% through caesarean section among meconium stained liquor cases. Microscopically, free meconium consists of amorphous green-brown material and anucleate squames. The amniotic epithelium exposed to meconium shows degenerative changes including heaping, stratification, ballooning degeneration and eventually nuclear pyknosis and necrosis. With time, meconium is engulfed by macrophages in the amnion, chorion, and deciduas. Meconium is usually scant in the umbilical cord due to the paucity of macrophages. To investigate whether meconium causes vasoconstriction, Altshuler et al. [10] tested umbilical vein tissue with an isometric transducer connected to a polygraph. They hypothesized that meconium may cause placental and umbilical cord vasoconstriction, cerebral and other fetal hypoperfusion, and major poor outcome. According to Ziadie M.[11], meconium induced changes to placenta may be graded depending upon the exposure time of meconium mainly by the presence of meconium filled macrophages in the placental membranes. This study had shown significant association between meconium stained liquor and neonatal depression evaluated by Apgar score.
Apgar score was devised in 1952 by the eponymous Dr. Virginia Apgar as a simple and repeatable method for quickly and summarily assesses the health of newborn children immediately after birth and to diagnose fetal distress at birth [23]. Apgar was an anesthesiologist who developed the score in order to ascertain the effects of obstetric anesthesia on babies. It has a continuous value in detecting fetal distress at birth for many years [24,25].
From that time, numerous studies [19,26-31] have demonstrated lower 1 and 5 minute APGAR scores in cases of thick meconium and increased incidence of caeserean sections and maternal and perinatal foetal morbidity. In our study, 1 minute Apgar score shows no depression in 17.1%, mild depression in 60.9% and severe depression in 22% cases of meconium stained liquor. Mild and severe depression is present in meconium stained liquor group only. All clear liquor cases (controls) have no depression. At 5 minutes Apgar score no depression was observed in 73.2% of newborns, mild depression in 24.4% and severe depression in 2.4% of meconium stained liquor. Mild and severe depression is present in meconium stained liquor cases only. These findings are statistically significant. So, both 1 and 5 minutes Apgar scores are lower (denoting depression) in meconium stained liquor group in comparison to clear liquor. Similarly, Misao et al. [2] noted increased incidence of low Apgar score in their study. Arulkumaran et al. [4] also found low 1 minute Apgar score and more admission of the newborns in special baby care unit. Zhu et al. [20] noted average Apgar score in meconium stained amniotic fluid group was lower than that in normal amniotic fluid group (P = 0.001). Ramchandra et al. [5] found higher incidence of low Apgar score (0-7) at one minute in study group as compared to the control, but no significant difference was found in the Apgar score at 5 minutes.
A significant association was also noted between Apgar score and several microscopical changes in placentas of meconium stained liquor.
When association between Apgar score (both at 1 and 5 minutes) and placental changes are assessed, it is seen that color of placenta, color of membrane and most of the microscopical changes noted here, are significantly higher in meconium group in comparison to clear group, except villitis and infarction. Most changes are related to villous structures. These are increase in intervillous space, intravillous fibrinoid, perivillous fibrinoid, calcification, fibrosis, syncytial knots, blood vessel changes (especially, fetal thrombotic vasculopathy). These changes are statistically significant (p- value: <0.05) in meconium stained liquor group in comparison to clear liquor group. Though, villitis (6.1%) and infarction (1.2%) are not statistically significant (p- value: >0.05) in this study. No change was noted in umbilical cord both in control group and cases.
In the fetal membrane, (i.e.: amnion and chorion) we
found multi-layering of amniotic epithelium in significant
number of the cases (Amnion epithelial hyperplasia)
and chorio-amnionitis in 15 cases, which are statistically
significant findings (p- value: <0.05) in meconium group
in comparison to clear liquor group. However, meconium
laden macrophages in amnion or chorion are noted in only
3 cases of meconium stained liquor, may be because of early
intervention in a tertiary care center. Necrosis or ballooning
degeneration of chorion and amnion are not found in any
cases of study population. Villous chorangiosis is a peculiar
finding in this study. It is present in 13.4% of total cases
(72.7% in meconium stained liquor group and 27.3% in
clear liquor group). But the finding is not statistically
significant (p- value: 0.067 (>0.05)). But, Altshuler [32]
found it to be a sign of neonatal morbidity and mortality. A
study by Kaspar et al. [33], described 9 different pathologic
lesions of the placenta. Among those, the frequency of
villous vascular thrombosis (25.4%), infarcts (38%), acute chorioamnionitis (20%), villous edema (9.1%) and villitis
(14.5%) was significantly higher in the group with longer
meconium exposure. Somewhat closely we have also found
many changes in villi. Though in our study, villous oedema
is not present; villitis and infarction are not significant
finding in the present study. Kariniemi et al. [
This study also suggests, that vascular changes in villous
structures are possibly present due to placental insufficiency,
causal factor for fetal distress and meconium passage,
either due to maternal or due to fetal hypoperfusion,
and not the effect of long standing meconium exposure.
Redline et al. [35], Sienko and Altshuler [36], Altshuler et
al. [37], demonstrated muscle necrosis of umbilical vessels
with prolonged meconium exposure. Ziadie [11] described
meconium laden pigmented macrophages with apoptotic
like nuclei present in different parts of placenta. However,
this study did not show this type of microscopical feature,
significantly. We found more changes in villi, fewer changes
in amnion and chorion, no change in umbilical cord at all.
It had previously been observed that intra-uterine fetal
distress is the consequences of maternal and fetal vascular
compromise, though the normal placenta has considerable
functional reserve [1]. This study also revealed that various
placental changes observed in meconium stained liquor
and associated neonatal outcome are mostly the features of
fetal thrombotic vasculopathy as well as fetal and maternal
hypoperfusion. Intra-villous and peri-villous fibrinoid,
increase inter-villous space, fibro-muscular sclerosis of
fetal vessels with or without calcification and luminal
obstruction as observed in this study are the features of
vascular compromise.
In conclusion, we can postulate that, villi changes
of placenta, most importantly arises out of vascular
compromise in villi may be the primary cause which gives
rise to fetal distress and thereby passage of meconium in
utero, possibly arises out of chronic placental hypoxia.
Fetal thrombotic vasculopathy, characterized by increased
intra- and peri- villous fibrinoid, exaggerated syncytial
knots, villous fibrosis and fibro-muscular sclerosis may be
the cause behind chronic placental hypoxia. The changes
which are described in various studies, like changes in
umbilical cord and fetal membrane are not present in this
study, may be due to early intervention of the meconium
stained liquor cases and thus changes associated with
chronic meconium exposure were not detected in this small
study group. Elaborate cross-sectional study is necessary for further comments regarding placental changes in
meconium exposure with time and its effect on neonatal
outcome.
ACKNOWLEDGEMENT
FUNDING
CONFLICT of INTEREST
The authors thank all staffs of Department of Pathology,
Burdwan Medical College for support and help in this
research work.
The authors confirm that they are all employee of
Government of West Bengal, India and have no corporate
affiliations. No funding has been received to do this
research work.
The authors declare no conflict of interest.
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