Twin chorionicity-specific population birth-weight charts adjusted for estimated fetal weight.

OBJECTIVES: To construct chorionicity-specific birth-weight reference charts for dichorionic diamniotic (DCDA) and monochorionic diamniotic (MCDA) twin pregnancies, incorporating estimated-fetal-weight (EFW) data in order to adjust for the relationship between suboptimal growth and preterm delivery. An additional aim was to determine if the inclusion of complicated twin pregnancies impacts on the reference charts produced. METHODS: The inclusion criteria for this retrospective cohort study were twin pregnancy of known DCDA or MCDA chorionicity, known pregnancy outcome, last ultrasound scan within 14 days before birth and delivery between 25 and 38 weeks' gestation (Analysis A). An analysis was also conducted excluding pregnancies with complications recorded (Analysis B). Previously published twin EFW reference ranges were used in the analysis. A joint statistical model for EFW and observed birth weight for each pregnancy was created in order to estimate population birth-weight reference ranges corresponding to the distribution expected if all pregnancies delivered at any given gestational age. It was not assumed that the median EFW was equal to birth weight for any given gestational age. The models were fitted using a Bayesian approach. RESULTS: We retrieved data on 1664 twin pregnancies, of which 707 DCDA and 241 MCDA pregnancies met the inclusion criteria. In Analysis A, the estimated population median birth weight was similar to the median EFW at around 27 weeks' gestation but fell below the EFW values with increasing gestation, being 156 g lower in both DCDA and MCDA pregnancies at 35 weeks; this finding was confirmed by direct comparison of the last EFW and birth-weight values in each pregnancy. When the analysis was repeated after excluding complicated twin pregnancies (Analysis B), compared with Analysis A, there was very little difference in the median birth-weight results obtained across gestation. The largest absolute difference between Analyses A and B for DCDA twins was at 31, 32 and 33 weeks, with a 9-g lower median birth weight in Analysis A compared with Analysis B. The largest absolute difference for MCDA twins was greater than that for DCDA twins, with a 21-g lower median birth weight at 25 weeks in Analysis A compared with Analysis B. CONCLUSIONS: We have established population chorionicity-specific birth-weight reference charts for DCDA and MCDA twin pregnancies, corresponding to the range expected were all pregnancies to deliver at any given gestational age. In this population of twins, the median birth weight was consistently lower than that reported for singletons, and there was variation in the median birth weight at different gestational ages according to chorionicity. © 2021 The Authors. Ultrasound in Obstetrics & Gynecology published by John Wiley & Sons Ltd on behalf of International Society of Ultrasound in Obstetrics and Gynecology. - Legal Statement: This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made.

Effect of monochorionicity on perinatal outcome and growth discordance in triplet pregnancy: collaborative multicenter study in England, 2000-2013.

OBJECTIVES: To compare perinatal outcome and growth discordance between trichorionic triamniotic (TCTA) and dichorionic triamniotic (DCTA) or monochorionic triamniotic (MCTA) triplet pregnancies. METHODS: This was a multicenter cohort study using population-based data on triplet pregnancies from 11 Northern Survey of Twin and Multiple Pregnancy (NorSTAMP) maternity units and the Southwest Thames Region of London Obstetric Research Collaborative (STORK) multiple pregnancy cohort, for 2000-2013. Perinatal outcomes (from ≥ 24 weeks' gestation to 28 days of age), intertriplet fetal growth and birth-weight (BW) discordance and neonatal morbidity were analyzed in TCTA compared with DCTA/MCTA pregnancies. RESULTS: Monochorionic placentation of a pair or trio in triplet pregnancy (n = 72) was associated with a significantly increased risk of perinatal mortality (risk ratio, 2.7 (95% CI, 1.3-5.5)) compared with that in TCTA pregnancies (n = 68), due mainly to a much higher risk of stillbirth (risk ratio, 5.4 (95% CI, 1.6-18.2)), with 57% of all stillbirth cases resulting from fetofetal transfusion syndrome, while there was no significant difference in neonatal mortality (P = 0.60). The associations with perinatal mortality and stillbirth persisted when considering only pregnancies not affected by a major congenital anomaly. DCTA/MCTA triplets had lower BW and demonstrated greater BW discordance than did TCTA triplets (P = 0.049). Severe BW discordance of > 35% was 2.5-fold higher in DCTA/MCTA compared with TCTA pregnancies (26.1% vs 10.4%), but this difference did not reach statistical significance (P = 0.06), presumably due to low numbers. Triplets in both groups were delivered by Cesarean section in over 95% of cases, at a similar gestational age (median, 33 weeks' gestation). The rate of respiratory (P = 0.28) or infectious (P = 0.08) neonatal morbidity was similar between the groups. CONCLUSIONS: Despite close antenatal surveillance, monochorionic placentation of a pair or trio in triamniotic triplet pregnancy was associated with a significantly increased stillbirth risk, mainly due to fetofetal transfusion syndrome, and with greater size discordance. In liveborn triplets, there was no adverse effect of monochorionicity on neonatal outcome. © 2020 International Society of Ultrasound in Obstetrics and Gynecology.

Chromosomal abnormalities detected by karyotyping and microarray analysis in twins with structural anomalies.

OBJECTIVES: To evaluate the incidence and types of chromosomal abnormalities detected in twins with structural anomalies and compare their distribution according to chorionicity and amnionicity and by structural-anomaly type. The added value of chromosomal microarray analysis (CMA) over conventional karyotyping in twins was also estimated. METHODS: This was a single-center, retrospective analysis of 534 twin pregnancies seen over an 11-year period, in which one or both fetuses were diagnosed with congenital structural anomalies on ultrasound. The ultrasound findings and invasive prenatal diagnostic results were reviewed. Twin pregnancies were categorized as monochorionic monoamniotic (MCMA), monochorionic diamniotic (MCDA) or dichorionic diamniotic (DCDA). Chromosomal abnormalities detected by G-banding karyotyping and/or CMA were analyzed by chorionicity and amnionicity and by structural-anomaly type. RESULTS: The 534 twin pairs analyzed comprised 25 pairs of MCMA, 112 pairs of MCDA and 397 pairs of DCDA twins. Of the 549 fetuses affected by structural anomalies, 432 (78.7%) underwent invasive prenatal testing and cytogenetic results were obtained. The incidence of overall chromosomal abnormalities in the DCDA fetuses (25.4%) was higher than that in the MCMA (3.7%) and MCDA (15.3%) fetuses. The incidence of aneuploidy was significantly higher in the DCDA group (22.8%) than in the MCMA (0.0%) and MCDA (12.4%) groups. The incidence of chromosomal abnormalities detected in fetuses, with anomalies of the cardiovascular, faciocervical, musculoskeletal, genitourinary and gastrointestinal systems, was higher in the DCDA group than in the MCDA group. In both the DCDA and MCDA groups, hydrops fetalis was associated with the highest incidence of chromosomal abnormality; of these fetuses, 67.6% had Turner syndrome (45,X). Pathogenic copy-number variations (CNVs) undetectable by karyotyping were identified by CMA in five (2.0%; 95% CI, 0.3-3.7%) DCDA fetuses. No pathogenic CNVs were found in MCMA and MCDA twins. CONCLUSIONS: Dichorionic twins with structural anomalies have a higher risk of chromosomal abnormalities, especially aneuploidies, than do monochorionic twins. The incremental diagnostic yield of CMA over karyotyping seems to be lower (2.0%) in twins than that reported in singleton pregnancy. Copyright © 2019 ISUOG. Published by John Wiley & Sons Ltd.

Placentation in watersnakes II: Placental ultrastructure in Nerodia erythrogaster (Colubridae: Natricinae).

Ultrastructure of the placental tissues from redbelly watersnakes (Nerodia erythrogaster) was analyzed during late pregnancy to provide insight into placental development and function. Examination of the chorioallantoic placenta with transmission electron microscopy reveals that chorionic and uterine epithelia are extremely attenuated but intact and that the eggshell membrane is vestigial and lacks a calcareous layer. These features minimize the interhemal diffusion distance across the placenta. Scanning electron microscopy reveals that fetal and maternal components of the placentas are richly vascularized by dense networks of capillaries. Although the yolk sac omphalopleure has largely been replaced by chorioallantois by late gestation, it retains patches of yolk droplets and regions of absorptive cells with microvilli and abundant mitochondria. Transmission electron microscopy reveals that yolk material is taken up for digestion by endodermal cells. As yolk is removed, allantoic capillaries invade to occupy positions just beneath the epithelium, forming regions of chorioallantoic placentation. Ultrastructural features indicate that the chorioallantoic placenta is specialized for gas exchange, while the omphalallantoic ("yolk sac") placenta shows evidence of functions in yolk digestion and maternal-fetal nutrient transfer. Placental features of this species are consistent with those of other thamnophines, and are evolutionarily convergent on snakes of other viviparous clades.

Placentation in watersnakes I: Placental histology and development in North American Nerodia (Colubridae: Natricinae).

As part of a broad survey of placental structure, function, and evolution in reptilian sauropsids paraffin-section histology was used to study microscopic anatomy of the uterus and fetal membranes of three species of North American watersnakes (Nerodia: Colubridae). The pre-ovulatory uterus is poorly vascularized with inactive shell glands. These shell glands are activated during vitellogenesis but regress during pregnancy. Two placentas develop through apposition of the uterine lining to the chorioallantois and the yolk sac omphalopleure. Fetal and maternal components of the chorioallantoic placenta are progressively vascularized during development. Their epithelia are attenuated, but (contrary to a previous report), epithelia of neither the uterus nor the chorion are eroded. The fetal portion of the yolk sac placenta is an omphalallantois, formed of avascular omphalopleure, isolated yolk mass, and allantois. This placenta is progressively replaced by chorioallantoic placenta during mid- to late-development through depletion of the isolated yolk mass. The chorioallantoic placenta is anatomically specialized for maternal-fetal gas exchange, and its expansion during development reflects the growing needs of the fetus for gas exchange. The yolk sac placenta is morphologically unsuited for gas exchange, but may serve other functions in maternal-fetal exchange.

A review of the mechanisms and evidence for typical and atypical twinning.

The mechanisms responsible for twinning and disorders of twin gestations have been the subject of considerable interest by physicians and scientists, and cases of atypical twinning have called for a reexamination of the fundamental theories invoked to explain twin gestations. This article presents a review of the literature focusing on twinning and atypical twinning with an emphasis on the phenomena of chimeric twins, phenotypically discordant monozygotic twins, mirror-image twins, polar body twins, complete hydatidiform mole with a coexistent twin, vanishing twins, fetus papyraceus, fetus in fetu, superfetation, and superfecundation. The traditional models attributing monozygotic twinning to a fission event, and more recent models describing monozygotic twinning as a fusion event, are critically reviewed. Ethical restrictions on scientific experimentation with human embryos and the rarity of cases of atypical twinning have limited opportunities to elucidate the exact mechanisms by which these phenomena occur. Refinements in the modeling of early embryonic development in twin pregnancies may have significant clinical implications. The article includes a series of figures to illustrate the phenomena described.

Caracterización de estadios del desarrollo embrio-fetal, vesícula coriónica y de placenta en la gata doméstica (Felis catus) mediante método ecográfico / Characterization of stages of embrio-fetal, chorionic vesicle and placenta development in the domestic cat (Felis catus) by ultrasonography

La ecografía es uno de los métodos de diagnóstico gestacional más utilizados, que permite confirmar una gestación temprana y realizar seguimientos del desarrollo embrio-fetal. En este estudio se emplearon 10 gatas gestantes, entre 10 meses a 6 años de edad, con fecha de cruza conocida. Se realizaron exámenes ecográficos seriados en los días 15 (estadio 1), 18 (estadio 2), 21 (estadio 3), 38 (estadio 4), y 45 (estadio 5) de gestación para medir parámetros biométricos. Vesícula coriónica: diámetro transversal (DTVC), diámetro longitudinal (DLVC); Placenta: grosor (GP); Feto: longitud céfalo-caudal (LCC), diámetro toraco-abdominal (DTA), diámetro cefálico (DC), tomándose un registro fotográfico de cada estadio. En el estadio 1, no se logró visualizar el embrión. En el estadio 2, el embrión se observó cercano a la pared midiendo en promedio 4,7 milímetros de LCC, el tubo endocárdico se observó funcional. En el estadio 3, se observó el cordón umbilical, pero resultó difícil distinguir los diferentes órganos, excepto el corazón, debido al movimiento causado por sus latidos. En el estadio 4, el feto adquiere movimientos, se observó órganos como el encéfalo, pulmones, el tabicamiento del corazón, diafragma, hígado, estómago, asas intestinales, vejiga y la osificación de huesos. Se observó la flexión de los miembros. En los miembros anteriores se visualizaron los dedos separados, con garras y cojinetes plantares. En el estadio 5, además de las características observadas en el estadio anterior, los riñones muestran la corteza y médula, las cámaras del corazón se visualizaron claramente. Se realizó una correlación lineal entre los parámetros biométricos estudiados y los resultados dieron valor significativo (p<0,0001) para la mayoría de éstos. Se logró caracterizar los estadios gestacionales estudiados. Siete de las diez gatas presentaron una gestación normal, mientras que una de ellas presentó en uno de sus fetos una malformación congénita y en las otras dos gatas se presentó muerte embrio-fetal.

Ultrasound is one of the most widely used methods for gestational diagnosis, allowing the detection of early pregnancy and evaluation of fetal growth and development. Ten pregnant cats (aged 10 months to-6 years) were used in this study, with known dates of mating. Serial ultrasound testings were performed on days 15th (stage 1), 18th (stage 2), 21st (stage 3), 38th (stage 4) and 45th (stage 5) of gestation, to measure biometric parameters (Chorionic vesicle: transverse diameter (DTVC), longitudinal diameter (DLVC); Placenta: thickness (GP); Fetus: cephalocaudal length (LCC), thoraco-abdominal diameter (DTA), cephalic diameter (DC). Photographic records were made at each stage. In stage 1, it was impossible to visualize the embryo. In stage 2, the embryo was observed near the wall measuring 4.7 mm on average LCC, and the endocardial tube was functioning. In stage 3, the umbilical cord was observed, but it was difficult to distinguish different organs, with the exception of the heart, which was detected by heartbeat movements. In stage 4, the fetus begins to move. Organs, such as the brain, lungs, heart septation, diaphragm, liver, stomach, bowel, bladder and bone ossification were observed. In the forelimbs, fingers apart with claws and footpads were visualized. In stage 5, in addition to the features observed in the previous stage, the kidneys show the cortex and medulla, and the heart chambers are clearly visualize. A linear correlation analysis among the biometric parameters was performed. Results were statistically significant for most parameters studied (p<0.0001). We characterized the gestational stages studied. Out of the ten cats studied, seven cats had a normal pregnancy. One cat showed one congenitally malformed fetus, and one fetal death occurred in the other two cats.

The structure and ultrastructure of the egg capsule of Brachyptera risi (Plecoptera, Nemouroidea, Taeniopterygidae) with some remarks concerning choriogenesis.

The organization of the egg capsule of the euholognathan stonefly, which represents the family Taeniopterygidae (Nemuroidea) was investigated using light and electron microscopy techniques. The presence of a complex, multilayered egg capsule, composed of a vitelline envelope, multilayered chorion, and extrachorion is described. The morphology of the eggshell of Brachyptera risi was compared with that of euholognthan and systellognathan egg coverings and the ground plan of the egg capsule in Plecoptera was discussed.

[Embryochorionic insufficiency: anatomic and physiologic prerequisites, rationale, definitions and pathogenetic mechanisms].

The paper provides a rationale for the new concept--embryochorionic insufficiency as a combined pathological response of extraembryonic structures and an embryo to different maternal exo- and endogenous disorders; it gives rise to early spontaneous abortions and non-developing pregnancies. The main pathogenetic mechanisms of embryochorionic insufficiency are: 1) endometrial structural incompetence; 2) dyschronism in the development of the extraembryonic coelom, amniotic cavity, yolk sac, and early placenta; 3) insufficient cytotrophoblast invasion; 4) discordant hemodynamic relationships; 5) blood rheological disorders; 6) local inflammation (endometritis); 7) oxidative stress; 8) secondary changes in the placental villi; 9) compensatory responses.

Effect of nanoparticle stabilization and physicochemical properties on exposure outcome: acute toxicity of silver nanoparticle preparations in zebrafish (Danio rerio).

Nanotechnology has vast potential for expanded development and novel application in numerous sectors of society. With growing use and applications, substantial production volumes and associated environmental release can be anticipated. Exposure effect of nanoparticles (NP) on biological systems may be intrinsic to their physicochemical properties introducing unknown associated risk. Herein, we expand the knowledge of health and environmental impact of silver nanoparticles (AgNPs), testing the acute toxicity of 14 AgNP preparations on developing zebrafish embryos (Danio rerio). Toxicological end points, including mortality, hatching rate, and heart rate were recorded. Concentration, stabilization agent and physicochemical properties were monitored as contributing outcome factors. Our findings indicate wide ranging LC50 24 h postfertilization values (0.487 ppm (0.315, 0.744 95% CI) to 47.89 ppm (18.45, 203.49 95% CI)), and indicate surface charge and ionic dissolution as key contributory factors in AgNP exposure outcome.

[Main components of gene network controlling development of dorsal appendages of egg chorion in Drosophila melanogaster].

The development of dorsal appendages of the chorion (specialized structures in the D. melanogaster egg which look like elastic tubes and ensure the breathing of the developing embryo) is an attractive model for the study of genetic mechanisms of the development of organs and tissues, whose generation is based on transformation of the epithelial tissue in the tubular structures. In the present review, we present information on genes and proteins that control the development of dorsal appendages of the chorion. We demonstrated that three signal pathways (EGFR, DPP, and NOTCH), which are combined together in a single gene network through a number of components, play a major role in the development of dorsal appendages of the chorion.

Development of yolk sac and chorioallantoic membranes in the Lord Howe Island skink, Oligosoma lichenigerum.

Development of the yolk sac of squamate reptiles (lizards and snakes) differs from other amniote lineages in the pattern of growth of extraembryonic mesoderm, which produces a cavity, the yolk cleft, within the yolk. The structure of the yolk cleft and the accompanying isolated yolk mass influence development of the allantois and chorioallantoic membrane. The yolk cleft of viviparous species of the Eugongylus group of scincid lizards is the foundation for an elaborate yolk sac placenta; development of the yolk cleft of oviparous species has not been studied. We used light microscopy to describe the yolk sac and chorioallantoic membrane in a developmental series of an oviparous member of this species group, Oligosoma lichenigerum. Topology of the extraembryonic membranes of late stage embryos differs from viviparous species as a result of differences in development of the yolk sac. The chorioallantoic membrane encircles the egg of O. lichenigerum but is confined to the embryonic hemisphere of the egg in viviparous species. Early development of the yolk cleft is similar for both modes of parity, but in contrast to viviparous species, the yolk cleft of O. lichenigerum is transformed into a tube-like structure, which fills with cells. The yolk cleft originates as extraembryonic mesoderm is diverted from the periphery of the egg into the yolk sac cavity. As a result, a bilaminar omphalopleure persists over the abembryonic surface of the yolk. The bilaminar omphalopleure is ultimately displaced by intrusion of allantoic mesoderm between ectodermal and endodermal layers. The resulting chorioallantoic membrane has a similar structure but different developmental history to the chorioallantoic membrane of the embryonic hemisphere of the egg.

Prospective risk of late stillbirth in monochorionic twins: a regional cohort study.

OBJECTIVE: Monochorionic (MC) pregnancies are routinely delivered electively at late preterm gestation with the aim of avoiding stillbirth at term. The aim of this study was to evaluate the prospective risk of late stillbirth in a large regional cohort of twin pregnancies of known chorionicity. METHODS: This was a retrospective study of all twin pregnancy births of known chorionicity between 2000 and 2009 from a large regional cohort consisting of nine hospitals. Prospective risk was calculated per 1000 fetuses rather than pregnancies, as each twin pregnancy had two gestations at risk of stillbirth. RESULTS: A total of 3005 twin pregnancies delivered after 26 weeks' gestation in the Southwest Thames Obstetric Research Collaborative. The total risk of stillbirth after 26 weeks in MC twins (19.1 per 1000 fetuses) was significantly higher than in dichorionic (DC) twins (6.5 per 1000 fetuses), with an odds ratio (OR) of 2.97 (95% CI, 1.71-5.18). The risk of stillbirth in MC twins did not change significantly between 26 weeks (1.8 per 1000 fetuses) and 36 weeks (3.4 per 1000 fetuses), with an OR of 1.85 (95% CI, 0.3-13.2). The equivalent figures for DC twins were 0.6 per 1000 fetuses and 2.1 per 1000 fetuses, respectively (OR, 3.4 (95% CI, 0.9-13.2)). CONCLUSIONS: The risk of stillbirth in MC twins does not appear to increase significantly near term. This may be due to a policy of routine surveillance and elective delivery from 36 weeks. The data do not support a policy of elective delivery before 36 weeks' gestation in MC pregnancies.

Lineage Commitments: Emphasis On Embryonic-Extraembryonic Interfaces.

The EMBO Workshop on 'Lineage Commitments: Emphasis on Embryonic-Extraembryonic Interfaces', held in May 2011, demonstrated that embryonic and extraembryonic tissues play early and significant interacting roles that mutually promote each other's further and correct deployment within the mammalian conceptus. Highlighted here are those presentations that directly addressed embryonic-extraembryonic interfaces in building the mammalian fetus.

Amnion formation in the mouse embryo: the single amniochorionic fold model.

BACKGROUND: Despite the detailed knowledge obtained over the last decade on the molecular regulation of gastrulation in amniotes, the process of amnion development has been poorly described and illustrated in mice, and conflicting descriptions exist. Understanding the morphogenesis and development not only of the early mouse embryo, but also of its extraembryonic tissues, is crucial for correctly interpreting fate-mapping data and mouse mutants with gastrulation defects. Moreover, the recent isolation from amnion of cells with stem cell features further argues for a better understanding of the process of amnion formation. Here, we revisit the highly dynamic process of amnion formation in the mouse. Amnion development starts early during gastrulation and is intimately related to the formation of the exocoelom and the expansion of the amniotic fold. The authoritative description involves the fusion of two amniotic folds, a big posterior and a smaller anterior fold. We challenged this 'two amniotic folds' model by performing detailed histomorphological analyses of dissected, staged embryos and 3D reconstructions using historical sections. RESULTS: A posterior fold of extraembryonic ectoderm and associated epiblast is formed early during gastrulation by accumulation of extraembryonic mesoderm posterior to the primitive streak. Previously called the "posterior amniotic fold", we rename it the "amniochorionic fold" (ACF) because it forms both amnion and chorion. Exocoelom formation within the ACF seems not to involve apoptosis within the mesoderm. The ACF and exocoelom expand without disrupting the anterior junction of epiblast, extraembryonic ectoderm and visceral endoderm. No separate anterior fold is formed; its absence was confirmed in 3D reconstructions. Amnion and chorion closure is eccentric, close to the anterior margin of the egg cylinder: we name it the "anterior separation point". CONCLUSIONS: Here, we reconcile previous descriptions of amnion formation and provide new nomenclature, as well as an animation, that clarify and emphasize the arrangement of the tissues that contribute to amnion development and the dynamics of the process. According to our data, the amnion and the chorion are formed by a single amniochorionic fold initiated posteriorly. Finally, we give an overview on mutant mouse models with impaired amnion development.

Dynamic topology of the cephalochordate to amniote morphological transition: a self-organized system of Russian dolls.

This note presents a mechanistic explanation of the transition between the morphology of cephalochordates to that of amniotes. By a careful study of the morphogenetic movements which occur during the early stages of development of a typical amniote (a chicken embryo), we are able to show that the formation of a vertebrate body follows a sequence: first, formation of dorsal folds, then head and heart as dorsal and ventral folds, and finally another dorsal fold, which eventually builds up the chorion. This order has a physical origin linked to the velocity field of the tissue flow. These folds form at right angles to the flow direction, and the topology of the chordates flow is hyperbolic. This mechanism explains the differences between the successive bauplans, by the cumulate forward and backward movement of the flow. Eventually, the entire phenomenon can be described as a self-organized system of Russian dolls, by which the heart finds itself inside the embryo, and the embryo itself inside the chorion. In addition, the phenomenon has a mirror symmetry in the anterior and in the posterior part, thereby explaining naturally the existence of animals having a caudal heart.

VEGF-A promotes intussusceptive angiogenesis in the developing chicken chorioallantoic membrane.

OBJECTIVE: To assess the impact of vascular endothelial growth factor (VEGF) on intussusceptive angiogenesis. METHODS AND RESULTS: Polyurethane casts of the microvasculature of chicken chorioallantoic membrane (CAM) were prepared on embryonic days (E) 8, 10, 12, and 14. At light microscopy level, minute holes (<2 microm in diameter) and hollows (>2 microm) were observed in the casts. Transmission electron microscopy disclosed the minute holes to mainly represent transluminal pillars characteristic for intussusceptive angiogenesis. The numerical density of the holes/pillars was highest at an early (E8) and a late (E12-E14) stage. Only mRNA of VEGF-A-122 and VEGF-A-166 isoforms was detected in the CAM. The transcription rate of VEGF-A mRNA peaked on E8/9 and E12, while VEGF-A protein expression increased on E8/9 and E11/12 to rapidly decrease thereafter as determined by immunoblotting. At all time points investigated, VEGF-A immunohistochemical reactivity was restricted to cells of the chorionic epithelium in direct contact to the capillary plexus. When the VEGF-R-inhibitor PTK787/ZK222584 (0.1 mg/mL) was applied on E9 CAM, the microvasculature topology on E12 was similar to that on E10. CONCLUSIONS: The temporal course of intussusception corresponded to the expression of VEGF-A in CAM microvasculature. Inhibition of VEGF-signaling retarded intussusceptive-dependent capillary maturation. These data suggest that VEGF promotes intussusception.

Monochorionic diamniotic twin pregnancies pregnancy outcome, risk stratification and lessons learnt from placental examination.

Monochorionic diamniotic twin pregnancies have a more hazardous intrauterine stay than their dichorionic counterparts because of the vascular anastomoses that connect the two fetal circulations. The survival of monochorionic twins diagnosed in the first trimester is 89%. Twin-to-twin transfusion syndrome (TTTS) occurs in 9% and is the most important cause of death. Risk assessment by ultrasound scan in the first and early second trimester identifies a subgroup of monochorionic twins with a more than 70% risk of a complicated outcome and a survival rate of only 69%. For complicated monochorionic twin pregnancies, umbilical cord coagulation for selective feticide has a survival rate of 83% with a normal development in 92%. Umbilical cord coagulation also results in a good outcome for the healthy co-twin of a heterokaryotypic monochorionic pair. Unequally shared placentas have a more elaborate blood exchange, which reduces the birthweight discordance. In these cases, the anastomoses fulfill a beneficial role by increasing the availability of oxygen and nutrients to the twin on the smaller placental share. Pairs with early onset discordant growth have a higher mortality and a more unequally shared placenta than pairs with late onset discordant growth. Unequal placental sharing therefore appears to be the cause of early onset discordant growth, whereas a late intertwin transfusion imbalance may be involved in some cases with late onset discordant growth. Finally, placental examination after laser treatment for TTTS demonstrated that successful coagulation of all visible anastomoses cures TTTS. However, anastomoses can be missed and lead to a complicated pregnancy outcome.