The placenta and low birth weight

Correlation between histological signs of placental underperfusion and perinatal morbidity in late-onset small-for-gestational-age fetuses

OBJECTIVE

To investigate whether signs of placental underperfusion (PUP), defined as any maternal and/or fetal vascular pathology, confer an increased risk of neonatal morbidity in late-onset small-for-gestational-age (SGA) fetuses with normal umbilical artery (UA) Doppler indices.

METHODS

A cohort of 126 SGA singleton fetuses with normal UA Doppler indices that were delivered after 34 weeks' gestation was studied. For each case, the placenta was evaluated histologically for signs of PUP using a hierarchical and standardized classification system. Neonatal morbidity was assessed according to the score calculated from the morbidity assessment index for newborns (MAIN), a validated outcome scale. The independent association between PUP and neonatal morbidity was evaluated using multivariable median regression analysis.

RESULTS

In 84 (66.7%) placentae, 97 placental histological findings that qualified as signs of PUP were observed. These PUP cases had a significantly higher incidence of emergency Cesarean section for non-reassuring fetal status (44.1% vs 21.4%, respectively; P = 0.013) and neonatal metabolic acidosis at birth (33.3% vs 14.3%, respectively; P = 0.023), than did those without PUP. The median MAIN score differed significantly between those with PUP and those without (89 vs 0, respectively; P = 0.025). This difference remained significant after adjustment for potential confounders. The proportion of cases with scores indicative of mild to severe morbidity was also significantly higher in the PUP group (31% vs 14.3%, respectively; P = 0.043).

CONCLUSION

In late-onset SGA fetuses with normal UA Doppler indices, signs of PUP imply a higher neonatal morbidity. These findings allow the phenotypic profiling of fetal growth restriction among the general population of late-onset SGA.

Association of Doppler parameters with placental signs of underperfusion in late-onset small-for-gestational-age pregnancies

OBJECTIVE

To elucidate the association between Doppler parameters and histological signs of placental underperfusion in late-onset small-for-gestational-age (SGA) babies.

METHODS

Umbilical, fetal middle cerebral and uterine artery pulsatility indices and umbilical vein blood flow (UVBF), which had been recorded within 7 days prior to delivery, were analyzed from a cohort of SGA singleton pregnancies delivered after 34 weeks' gestation and confirmed as having a birth weight < 10(th) percentile by local standards. In each case, the placenta was histologically evaluated for signs of placental underperfusion using a hierarchical and standardized classification system. The independent association of the Doppler parameters with placental underperfusion was evaluated using logistic regression and decision tree analysis.

RESULTS

In 51 cases (53.7%), there were 61 placental histological findings indicative of placental underperfusion. These cases had a significantly higher incidence of Cesarean section for non-reassuring fetal status (52.1% vs 11.9%; P < 0.001) and neonatal metabolic acidosis at birth (21.6% vs 0%; P = 0.001). Significant and independent contributions to the presence of placental underperfusion lesions were provided by increased mean UtA pulsatility index (PI) (P = 0.018; odds ratio (OR) 2 (95% CI, 1.1-3.7)) and decreased UVBF normalized to estimated fetal weight (P = 0.027; OR 0.97 (95% CI, 0.95-0.99)). The combination of both parameters revealed three groups with differing risks for placental underperfusion: normalized UVBF > 82 mL/min/kg (risk 31.3%), normalized UVBF ≤ 82 mL/min/kg and mean UtA-PI ≤ 95(th) percentile (risk 65.5%), and normalized UVBF ≤ 82 mL/min/kg and UtA-PI > 95(th) percentile (risk 94.4%).

CONCLUSIONS

In late-onset SGA pregnancies, uterine Doppler and UVBF are surrogates for placental underperfusion. These findings facilitate phenotypic profiling of cases of fetal growth restriction among the general population of late-onset SGA babies.

Development of the placental villous tree and its consequences for fetal growth

Co-ordinated development of the fetal villous tree of the placenta is necessary for continued fetal growth and well-being. Before fetal viability, blood vessel development within the developing immature intermediate villi (IIV) is characterized by branching angiogenesis, such that the placenta expands to produce 10-16 generations of stem villi. Once fetal viability is attained, a developmental switch occurs to form large numbers of gas-exchanging terminal villi (TV) by non-branching angiogenesis in mature intermediate villi (MIV). Several growth factors, including vascular endothelial growth factor (VEGF), placenta growth factor (PlGF), angiopoietins, and angiostatins are produced within the villi and act locally, via their receptors, to control angiogenesis. Their relative contributions to placental vascular development are not fully understood at the present time. Severe early-onset intrauterine growth restriction (IUGR) is characterized by absent/reversed end-diastolic flow velocity (ARED) in the umbilical arteries, leading to fetal hypoxia, acidosis and a substantial rise in perinatal mortality and morbidity. The placentas from such cases show a deficit in peripheral villous development, which may be perpetuated by the effects of oxygen (delivered by maternal blood into the intervillous space) upon VEGF-directed angiogenesis, the so-called 'placental hyperoxia' theory of villous maldevelopment. Trophoblast apoptosis is a significant feature of early-onset IUGR and may explain poor flow-independent transfer of nutrients to the fetus. Finally, since transgenic mouse studies highlight the importance of trophoblast-derived transcription factors for placental villous (labyrinth) development, it is possible that the villous trophoblast controls the orderly development of the underlying mesoderm and blood vessels into the fetal villi.

Branching patterns of human placental villous trees: perspectives of topological analysis

Topological analysis was applied to investigate the branching pattern of three specimens obtained from early human placenta (6, 9, and 16 weeks p.m.) reconstructed on the basis of semi-thin sections. Centripetal Horton-Strahler and centrifugal branching order nomenclature was used for topological description of the analysed tree-like structures. Bifurcation ratio and vertex ratio were determined for all three cases and were found to be relatively constant. It was shown that branching pattern is closely related to the model of random segment branching that implicates a high level of asymmetry and a small level of space limitation for branching. The significance of this approach for the analysis of development of the villous tree, for the analysis of mesenchymal villous heterogeneity, and for the estimation of physiological parameters for fetoplacental exchange is discussed. We suggest that topological analysis can lead to a new quantitative classification of branching patterns of the human placental villous trees in normal and pathologic pregnancies.

Placental morphology in relation to umbilical artery blood velocity waveforms

The association between umbilical artery flow velocity waveforms, placental morphology and arterial vascular pattern was investigated in 30 pregnant women at risk for intra-uterine growth retardation. The blood velocity waveform was assessed in the umbilical arteries with pulsed Doppler ultrasound. Placentas from fetuses with an end-diastolic zero flow were small and thick with an extrachorial configuration, marginal cord insertion, magistral or mixed allantochorial vessel pattern and few cotyledons. The incidence and the extension of gross lesions were slightly increased in these placentas compared to placentas from fetuses with a normal S/D ratio (peak systolic velocity/minimum diastolic velocity). Placentas from fetuses with an increased S/D ratio (greater than +2SD) were large and thin with a high maximum diameter/maximum thickness ratio. Heavily smoking mothers were overrepresented in the group, with an increased S/D ratio and corresponding SGA infants. End-diastolic zero flow in the umbilical artery was strongly correlated with placental developmental abnormalities.

Chorioamnionitis in relation to gestational outcome in a Swedish population

In a histopathological study, from a homogeneous Swedish population with a better than average socio-economic standard, placentas from 161 singleton infants small for gestational age (SGA) and 322 singleton infants appropriate for gestational age (AGA) were examined for the presence of inflammation in the placental parenchymal membranes, cord and decidua. Acute chorioamnionitis including funiculitis was found in 13.4% of the total material, in 17% of term AGA-infants (GA, greater than or equal to 38 weeks), in 13% of preterm AGA-infants (less than or equal to 37 weeks) and in 6.8% of SGA-infants (p less than 0.001, compared to term AGA). Acute chorioamnionitis was correlated to vaginal delivery (p less than 0.01), rupture of the membranes greater than 24 hours (p less than 0.01), nulliparity (p less than 0.05) and amniocentesis (RR = 1.7). In nulliparous, chorioamnionitis was related to duration of labor greater than 16 hours (p less than 0.01). Streptococcal (p less than 0.01) and anaerobic vaginal infections (p less than 0.05) were also related to chorioamnionitis. Of 17 infants with sepsis, 6 had chorioamnionitis (p less than 0.05). Decidual inflammation was chronic in type and found in 4.5% of the placentas and was not related to chorioamnionitis, but to parity (p less than 0.05) and term AGA-infants (p less than 0.001).

Placental lesions and maternal hemoglobin levels. A comparative investigation

A high maternal hemoglobin level during pregnancy has been correlated to a low birth weight and a low placental weight, but has not been investigated in relation to placental factors. In 330 consecutive deliveries, placental lesions, birth weight and placental weight were studied in a multiple regression analysis in relation to maternal hemoglobin concentration, taking into consideration possible confounding factors such as smoking, hypertensive disorders, weight gain, primiparity, gestational age and sex. A high maternal hemoglobin concentration (greater than 130 g/l) was correlated with a low birth weight, acute infarcts and syncytial knots. Intervillous thrombosis was more common in non-smokers and multiparous women, increasing in incidence as gestational age advanced. Infarcts and microscopic perivillous fibrin were correlated with hypertension. Microscopic perivillous fibrin was slightly associated with a high hemoglobin level (greater than 130 g/l) in a bivariate analysis. These findings may indicate that a high maternal hemoglobin level impairs the uteroplacental circulation.

Placental villitis and intrauterine growth retardation in a Swedish population

Villitis was studied in placentas from 445 singleton infants from an ethnically homogeneous population with a good socioeconomic standard. There were 161 infants small for gestational age (SGA) and 284 appropriate for gestational age (AGA). Villitis was found in 12 SGA-placentas (7.5 per cent) and 8 AGA placentas (2.8 per cent) (p less than 0.05). The degree of villitis was also related to growth retardation (p less than 0.05). Except for one placenta with villitis due to CMV infection, the cause of villitis could not be determined. No association was found with various studied factors such as hypertension, pre-eclampsia, smoking or maternal pyrexia during pregnancy.

Intrauterine growth retardation: morphometry of the microvillous membrane of the human placenta

The syncytiotrophoblast microvillous membrane of the human placenta has been investigated with quantitative analyses in cases of severe fetal growth retardation associated with a marked reduction in the surface area of exchange at the peripheral villous level. This study has shown that, in placentae of intrauterine growth-retarded infants of unknown origin, there were morphological changes in the microvillous membrane characterized by an increase in the microvillous surface density and surface enlargement factor, associated with a reduction of the intermicrovillous space. It is not possible to state whether these morphological changes represent a delayed maturation of the placental tissue, or compensatory mechanisms to improve the functional efficiency of the placenta. In pre-eclampsia, these placental changes were much less pronounced, possibly due to severe uteroplacental ischaemia in this complication of pregnancy. Despite these morphological changes, both groups of placentae showed significant reductions in absolute values for the microvillous and total trophoblastic surface areas, which can have major implications on the functional efficiency of the placenta.

Computerized ultrasonic image analysis for placental characterization in normal and hypertensive pregnancies

A technique has been developed for characterizing ultrasonic images of the human placenta by computerized image analysis. An ultrasonic image data base has been assembled from routine obstetric scans collected from 112 patients. A region within the placenta was manually identified in each image, and a series of parameters which mathematically describe the image texture in the region of interest was calculated. Our pilot study has shown that gestational age at scan, placental position and the presence or absence of hypertension can all be correlated with the mathematically defined textural descriptors of the ultrasonic placental image.

Chronic placentitis--a clinicopathological study

Between 1978 and 1983 1240 singleton placentas were examined macroscopically and histologically. In 82 cases (6.6%) a "chronic placentitis" was diagnosed. The pathognomonic inflammatory foci were localized within the placental villi. The vast majority showed mixtures of both fibrohistiocytes and lymphoid cells, which were occasionally interspersed with plasma-cells. The clinical data relating to 67 placentas were correlated retrospectively with the degree of inflammation. 46 showed mild and 21 moderate to severe chronic placentitis. In both of these groups the proportion of preterm deliveries and cases with preeclampsia was equally high. With increasing severity of chronic placentitis, however, there was a significant reduction in weight and size of both, placenta and infant, and the incidence of perinatal asphyxia was significantly raised.

The human placenta in idiopathic intrauterine growth retardation: a light and electron microscopic study

Six placentae from small for gestational age infants were examined by both light and electron microscopy. These were from pregnancies in which all maternal or fetal factors known to be associated with intrauterine growth retardation, including maternal cigarette smoking, were excluded. At the light microscopic level the only significant finding was an excess of villous cytotrophoblastic cells whilst electron microscopy showed these placentae to be characterized by villous cytotrophoblastic hyperplasia, focal syncytial necrosis, microvillous abnormalities, reduced syncytial secretory activity, irregular thickening of the trophoblastic basement membrane and the presence of small fetal villous vessels with multilayered basement membranes. It is thought that most of the observed abnormalities are due to uteroplacental ischaemia and it is possible that the fetal vascular abnormalities are a reflection of the fetal growth retardation. There is little evidence that the functional efficiency of the placenta is impaired in these cases and it is suggested that the principal factor in the pathogenesis of fetal growth retardation is a restriction of nutrient supply to the fetus because of an inadequate degree of physiological change within the maternal spiral vessels.

The fetal arterial vasculature in placentas of insulin-dependent diabetic mothers

Seventeen placentas from insulin-dependent diabetic women and ten placentas from non-diabetics were studied with angiography. The fresh placentas were injected in both umbilical arteries with barium sulphate suspension. After fixation in formaldehyde, the placentas were X-rayed, intact and after being sliced in 0.8 cm slices. There were two clearly distinguishable types of intracotyledonary arteries. Type A is long, narrow and usually runs in the periphery of the cotyledon; type B is wider and usually runs towards the centre of a cotyledon. The cotyledons were classified according to the distribution of these two types of arteries. Type I contained only A-arteries and Type II, both A- and B-arteries or only B-arteries. Twelve per cent of the cotyledons in the control group belonged to Type I, but in the diabetes group 29 per cent. One block of tissue from every placenta was examined histologically to check that the contrast medium filled the stem villus vessels but not the capillaries in the peripheral villi. The histological sections in both groups were compared. Endarteritis appeared to be a feature of the diabetes placenta. The angiographic findings were compared with results of previous direct light microscopical studies. A high percentage of hypovascular villi was found in placentas with a high number of Type I cotyledons.