Placental weight and neurologic outcome in the infant: a review

Genetic causal relationship between placental weight and autism spectrum disorder: A two-sample Mendelian randomization study

OBJECT

Previous research has suggested an association between placental tissue abnormalities and the diagnosis of autism spectrum disorder. This study aims to explore the causal relationship between placental weight and autism spectrum disorder.

METHODS

This study employed Mendelian randomization analysis to investigate the potential causal relationship between placental weight and autism spectrum disorder. The study design involved two sample populations, with data for the exposed population sourced from previous studies focusing on PW, and data for the outcome population obtained from the Integrative Psychiatric Research and the Psychiatric Genomics Consortium study. To ensure the robustness of the results, three sensitivity analyses were performed, including heterogeneity testing, pleiotropy testing, and a leave-one-out analysis. The inverse variance weighted method served as the gold standard for the Mendelian randomization analysis.

RESULTS

The results of the first analysis revealed a significant correlation between an increase in placental weight and an elevated risk of autism spectrum disorder (p = 0.02). Sensitivity analysis detected heterogeneity and outliers. After removing two outlier SNPs in the second round of analysis, the results still supported a genetic causal relationship between placental weight and autism spectrum disorder (p = 0.01). The second-round sensitivity analysis did not reveal any heterogeneity or outliers.

CONCLUSION

Our study provides compelling evidence supporting a causal relationship between elevated placental weight and increased risk of autism spectrum disorder. These findings underscore the significance of placental development in the etiology of autism spectrum disorder and propose a potential early predictive indicator for autism spectrum disorder.

Reference Values for Placental Weight and Placental:Fetal Weight Ratio in a Swedish Population

INTRODUCTION

There is important clinical information from placental weight and its ratio to the fetal weight. The aim with this study was to establish reference values for the placental weight and the placental:fetal weight ratio for gestational weeks 13-43 in a Swedish population.

MATERIALS AND METHODS

Cases were retrospectively collected from the database used at the Pathology Department at Karolinska University Hospital and information about the placental weight, fetal weight, and gestational age was retrieved. Conditions, which could affect the placental- or fetal weight were excluded. Thereafter percentile curves were calculated for the placental weight and the placental:fetal weight ratio for gestational weeks.

RESULTS

A total of 730 cases were included and percentile curves for the placental weight for gestational week 13-43 and placental:fetal weight ratio for gestational week 18-43 are presented.

CONCLUSIONS

Reference values for post fixation placental weight and its ratio to fetal weight for a Swedish population are presented. The reference values are lower than the current reference values used in our institution, and this will be of importance when interpreting findings after placental examination.

Placental size at gestational week 36: Comparisons between ongoing pregnancies and deliveries

INTRODUCTION

We aimed to compare placental size and placental size relative to fetal size (ratio) in ongoing pregnancies examined by magnetic resonance imaging (MRI) at gestational week 36 with placental size among all deliveries at gestational week 36 during the same time period.

MATERIAL AND METHODS

Ongoing unselected singleton pregnancies (n = 89) were examined by MRI at median gestational week 36+5 days during 2017-2018, and placental and fetal volumes (cm3 ) were calculated. The placental size and ratio in ongoing pregnancies were compared with placental size and ratio among all deliveries in Norway at gestational week 36 (median gestational week 36+4 days) during 2016-2019 (n = 5582). For comparison of size, we converted volume (cm3 ) in ongoing pregnancies into grams as: cm3  × 1.05 (density of placental and fetal tissue).

RESULTS

In ongoing pregnancies, median placental size was 873  (interquartile range [IQR] 265) grams and median size of all delivered placentas was 613 (IQR 290) grams. Placental size was smaller among the delivered placentas independent of delivery mode: 760 (IQR 387) grams among elective cesarean deliveries (n = 465) and 590 (IQR 189) grams among vaginal deliveries after spontaneous onset of labor (n = 2478). Median ratio in ongoing pregnancies was higher than among deliveries: 0.31 (IQR 0.08) vs 0.21 (IQR 0.08). The ratio was higher in ongoing pregnancies independent of delivery mode: 0.24 (IQR 0.17) among elective cesarean deliveries vs 0.21 (IQR 0.05) among vaginal deliveries after spontaneous onset of labor.

CONCLUSIONS

The placenta is larger in ongoing pregnancies than among deliveries. This finding suggests that placental size decreases during labor and delivery, possibly by transfer of blood to the fetus. Our finding also suggests that reference values of placental size based on delivered placentas are not valid for ongoing pregnancies.

Placental pathology and neonatal encephalopathy

Neonatal encephalopathy (NE) is an important cause of neonatal morbidity and mortality worldwide; however, there remain gaps in our knowledge about its pathogenesis. The placenta has been implicated in the pathogenesis of this disease but conclusive evidence related to the placental factors that influence it is sparse. This review aims to outline the current knowledge on the role of the placenta with particular attention to its role in NE as a consequence of hypoxia-ischemia. A total of 26 original articles/review papers were used to compile this review. Three themes were identified from these publications: fetal vascular malperfusion including umbilical cord pathology, inflammatory changes in the placenta, and maternal vascular malperfusion including placental weight. These features were identified as being significant in the development of NE. Advancing our understanding of this relationship between placental pathology and NE may facilitate the development of additional antenatal screening to better identify at-risk fetuses. We highlight areas for further research through antenatal screening and placental histology.

Placental pathology as a marker of brain injury in infants with hypoxic ischemic encephalopathy

BACKGROUND

Hypoxic Ischemic Encephalopathy (HIE) can lead to devastating consequences for the affected infant. Although therapeutic cooling benefits infants with moderate and severe HIE, differentiating mild from moderate-severe HIE may be challenging. The placenta reflects the fetal intrauterine environment and may reveal underlying processes that affect brain injury.

AIM

To describe placental histopathology using the Amsterdam Placental Workshop Group Criteria in different grades of HIE.

STUDY DESIGN

Retrospective cohort.

SUBJECTS

Infants admitted to a tertiary care neonatal intensive care unit with a diagnosis of HIE between 2011 and 2016.

OUTCOME MEASURE

Maternal and neonatal clinical variables and placental histopathology using the Amsterdam Placental Workshop Group Criteria were compared between mild and moderate-severe HIE. Mann-Whitney or t-test or ꭓ² were performed for bivariate associations as appropriate. To explain the relationship between placental pathology and severity of HIE odds ratios (ORs) and 95 % confidence intervals (CIs) were calculated using logistic regression models.

RESULTS

Of the 73 infants in the study, 23 had mild and 50 moderate-sever HIE. There was no difference in maternal and neonatal characteristics except for sentinel events which were higher in the moderate- severe group. On placental histopathology, acute inflammation, including fetal inflammatory reaction (FIR) were significantly higher in the moderate-severe group. After adjusting for confounders, FIR remained significantly associated with moderate-severe HIE, ORs 6.29, 95 % CI 1.5-25.

CONCLUSION

Our study demonstrates FIR in the placenta is associated with severity of HIE.

Placental Findings in Infants with Hypoxic-Ischemic Encephalopathy: The Importance of the Comparison Group

OBJECTIVE

To determine the effect of 3 distinct comparison groups on associations between placental abnormalities and neonatal hypoxic-ischemic encephalopathy (HIE).

STUDY DESIGN

This single-center, prospective case-control study of singletons of gestational age ≥36 weeks with predefined criteria for HIE (n = 30) and 3 control groups was conducted from June 2015 to January 2018. The control groups were infants born by repeat cesarean delivery (n = 60), infants born small for gestational age (SGA; n = 80), and infants receiving positive-pressure ventilation (PPV) at birth (n = 70). One pathologist blinded to infant category reviewed placental sections using the Amsterdam Placental Workshop criteria. Logistic regression with group contrasts relative to HIE was used to analyze primary placental pathologies, and ORs with 95% CIs provided effect sizes.

RESULTS

The odds of maternal vascular malperfusion were increased among HIE group placentas compared with placentas of the repeat cesarean delivery (OR, 4.50; 95% CI, 1.45-14.00) and PPV (3.88; 1.35-11.16) groups, but not those of the SGA group. The odds of fetal vascular malperfusion were increased in the HIE group compared with the SGA group (OR, 9.75; 95% CI, 1.85-51.51). The odds of acute chorioamnionitis were higher in the HIE group compared only with the repeat cesarean delivery group, reflecting a similar incidence of chorioamnionitis in SGA group and PPV group placentas. The absence of placental findings was lowest in the HIE group (6.7%), followed by the SGA (18.8%), PPV (31.4%), and repeat cesarean delivery (75%) groups.

CONCLUSIONS

Associations with placental abnormalities among infants with HIE varied based on the specific placental abnormality and the control group. Potentially important associations between placental pathology and HIE may be obscured if control groups are not well designed.

Weights of Fetal Membranes and Umbilical Cords: Correlation With Placental Pathology

INTRODUCTION

Proper placental gross examination requires weighing the placental disc trimmed of fetal membranes and the umbilical cord. However, untrimmed placental weights are often reported, both in cases submitted for consultation and in publications. Thus, determining the contribution of membranes and cords to untrimmed placental weights would be helpful in estimating the true trimmed weight of placentas. We sought to report the average weights of membranes and cord in term placentas and to correlate these weights with common placental pathologies.

METHODS

A total of 500 consecutive placentas delivered between 36 and 42 weeks gestational age were subjected to a modified grossing protocol, in which the weight of the trimmed and untrimmed placentas, fetal membranes, and umbilical cords were recorded. Acute chorioamnionitis, meconium, maternal vascular malperfusion, and fetal vascular malperfusion were included as pathologic correlates. Clinical data such as the presence of fetal hydrops, intrauterine growth restriction, intrauterine fetal demise, and maternal diabetes were also recorded.

RESULTS

The mean weights of the trimmed placenta, fetal membranes, and umbilical cords were 442 g (180-805 g), 47.2 g (16-108 g), and 37.9 g (9-126 g), respectively. The fetal membranes and umbilical cord weights contributed a mean of 16% to the total untrimmed placental weight. Meconium was associated with heavier fetal membranes. Fetal vascular malperfusion was associated with longer umbilical cord and thus also with heavier umbilical cords. Maternal vascular malperfusion and intrauterine growth restriction were associated with lighter placentas.

DISCUSSION

The trimmed placental disc weight may be estimated by subtracting 16% (ie, weight of the fetal membranes and umbilical cord) from the untrimmed placental weight, or alternatively by subtracting the mean weight of the membranes and umbilical cord. It is important to consider the effects of meconium, fetal and maternal vascular malperfusion, and intrauterine growth restriction on membrane and cord weights when estimating the trimmed placental disc weight.

Placental weights from normal deliveries in Ireland

BACKGROUND

The weight of the delivered placenta gives a useful representation of placental function in utero. In the absence of Irish data, many pathologists rely on data from other populations, many of which are now 15 to 30 years old. The development of a population-specific nomogram would aid in the examination of placentas after delivery, allowing pathologists and medical scientists to more easily distinguish between placental physiological changes and pathology.

AIMS

To record placental weights among women having a singleton delivery in Dublin and to establish median placental weights for each gestational age after 37 weeks.

METHODS

Prospective cohort study in a Tertiary level University Hospital. All singleton pregnancies were included; stillbirths, multiple gestations, and cases with obstetric complications involving the placenta were excluded. The placentas were weighed both untrimmed and trimmed with standard scales. Demographic features including birth weight and maternal parity were also recorded.

RESULTS

Four hundred thirty placentas were weighed over a 6-week period. A median term placental weight based on gestational age was established, with a range from the tenth to ninetieth centiles.

CONCLUSION

The weight of the placenta is one of several measurements that are easy to acquire, and when recorded in a systematic fashion, provide information not just on an individual, but also on a population basis. Birth weights have increased over the last century, and this study provides national data helping distinction between placental physiology and pathology.

Fetal programming and Wilms tumor

BACKGROUND

The "fetal programming" hypothesis has been evaluated in many adult diseases including cancer, but not for Wilms tumor. Wilms tumor has been related to high birthweight, but little is known about other growth metrics such as a baby's birth length, ponderal index, or placenta size, which can shed additional light on growth patterns.

METHODS

Cases of Wilms tumor (N = 217) were taken from the Danish Cancer Registry, and controls (N = 4340) were randomly selected from the Population Register and matched to cases by sex and age. Linkage to the Medical Births Registry provided information on gestational factors and fetal growth measurements, while linkage to the Patient Register provided information on maternal and child health conditions.

RESULTS

Despite having typically normal to higher birthweights, Wilms tumor cases had smaller placentas (≤540 g; odds ratio (OR) = 4.24; 95% confidence interval (CI), 1.84-9.78) and a lower placenta-to-birthweight ratio (OR = 1.81; 95% CI, 1.17-2.82, per 1 SD decrease). Small placentas were more common among Wilms cases without congenital anomalies (OR = 6.43; 95% CI, 1.95-21.21). Wilms tumor cases had a higher prevalence of high birthweight (>4000 g; OR = 1.57; 95% CI, 1.11-2.22), birth length 55 cm or longer (OR = 1.74; 95% CI, 1.09-2.78), and being large for gestational age (OR = 1.79; 95% CI, 1.08-2.96).

CONCLUSIONS

Our study corroborates earlier studies showing associations with high birthweight and suggests associations between Wilms tumor and decreased placental size and low placenta-to-birthweight ratio.

The role of morphology in mathematical models of placental gas exchange

The performance of the placenta as a gas exchanger has a direct impact on the future health of the newborn. To provide accurate estimates of respiratory gas exchange rates, placenta models need to account for both the physiology of exchange and the organ morphology. While the former has been extensively studied, accounting for the latter is still a challenge. The geometrical complexity of placental structure requires use of carefully crafted approximations. We present here the state of the art of respiratory gas exchange placenta modeling and demonstrate the influence of the morphology description on model predictions. Advantages and shortcomings of various classes of models are discussed, and experimental techniques that may be used for model validation are summarized. Several directions for future development are suggested.

Cerebral palsy: phenotypes and risk factors in term singletons born small for gestational age

BACKGROUND AND OBJECTIVES

Children born small for gestational age (SGA) are at increased risk of developing cerebral palsy (CP). The pathophysiology behind this association remains unclear. We compare the clinical profile of children with CP born SGA to other children with CP. We hypothesize that differences noted will support antenatal causes of CP in children born SGA.

METHODS

We conducted a retrospective cohort study of term singletons with CP, extracting data from the Canadian Cerebral Palsy Registry. SGA was determined as birth weight for gestational age and sex below the tenth percentile.

RESULTS

Mothers of children with CP born SGA were more likely to be of African-American ethnicity (RR 2.54, 95% CI 1.20-5.39), have intrauterine infections (RR 2.22, 95% CI 1.09-4.50) and have gestational hypertension (RR 1.78, 95% CI 1.06-3.00). Children with CP born SGA had smaller head circumferences at birth (p < 0.001) and higher frequencies of emergency cesarean-section (RR 1.53, 95% CI 1.22-1.92), birth asphyxia (RR 1.53, 95% CI 1.0-2.32), and placental abnormalities (RR 1.45, 95% CI 1.00-2.10). Children with CP born SGA had greater fine motor (RR 1.46, 95% CI 1.02-2.11), gross motor (RR 1.53, 95% CI 1.12-2.10) and communication impairment (RR 1.24, 95% CI 1.10-1.40), and a higher frequency of cognitive impairment (RR 1.33, 95% CI 1.06-1.69).

CONCLUSION

Children with CP born SGA have different clinical factors and phenotypic profiles than other children with CP. These differences support the hypothesis of antenatal and perinatal causes of CP in children born SGA. Future case control studies would be desired to further define this causal pathway.

Placental pathology and neurological morbidity in preterm infants during the first two weeks after birth

BACKGROUND

The placenta plays a crucial role during pregnancy and dysfunction causes long-term neurological problems. Identifying placenta-related risks for neurological problems shortly after birth may provide clues for early interventions aiming to improve neurological outcome.

OBJECTIVE

To determine the association between placental pathology and neurological morbidity in preterm infants during the first two weeks after birth.

STUDY DESIGN

Placentas of 52 singleton, preterm infants (GA: 25-31weeks, BW: 560-2250 grammes) were examined for histopathology. The infants' neurological condition shortly after birth was determined by assessing the quality of their general movements (GMs): normal, abnormal, or hypokinetic, on days 5, 8, and 15. A motor optimality score (MOS) was also assigned.

RESULTS

Examination of the placentas revealed maternal vascular underperfusion (n=29), ascending intrauterine infection (AIUI) (n=19), villitis of unknown aetiology (n=6), chronic deciduitis (n=11), foetal thrombotic vasculopathy (FTV) (n=9), and elevated nucleated red blood cells (NRBCs) as a marker for foetal hypoxia (n=7). None of the placental lesions were significantly associated with the quality of GMs or MOS.

CONCLUSIONS

This study indicated that placental lesions were not associated with infants' neurological condition as measured by the quality of their general movements during the first two weeks after birth.

Optimising sample collection for placental research

Biobanks provide an important repository of samples for research purposes. However, for those samples to reflect the in vivo state, and for experimental reliability and reproducibility, careful attention to collection, processing and storage is essential. This is particularly true for the placenta, which is potentially subjected to stressful conditions during delivery, and sample collection may be delayed owing to routine postpartum inspection by clinical staff. In addition, standardisation of the collection procedure enables samples to be shared among research groups, allowing larger datasets to be established. Here, we provide an evidence-based and experts' review of the factors surrounding collection that may influence data obtained from the human placenta. We outline particular requirements for specific techniques, and propose a protocol for optimal sample collection. We recognise that the relevance of these factors, and of the sample types collected to a particular study will depend on the research questions being addressed. We therefore anticipate that researchers will select from the protocol to meet their needs and resources available. Wherever possible, we encourage researchers to extend their collection to include additional samples that can be shared on an international collaborative basis, with appropriate informed consent, to raise the quality, as well as quantity, of placental research.