Bio activity of Preterm Labour

Prof. M.C. Bansal.MBBS. MS. MJCOG. FICOG.Founder Principal& Controller;Jhalawar Medical College And Hospital Jhalawar.Ex. Principal & Controller;Mahatma Gandhi Medical College And Hospital, Sitapura , Jaipur.

INTRODUCTION• Before onset of preterm labour, Uterine quiescence is

maintained as in other Pregnancies ---after initiation and establishment of preterm labour—all the events involved in all 4 phases of parturition occur in similar manner as in term Labour.

• Preterm Birth carry major adverse risks of human consequences.• After congenital anomalies it is the major cause of neonatal

morbidity and mortality.• Spontaneous preterm labour without Pre PROM occurs in > 50%

cases while rest 25 % have pre PROM before the onset of Preterm Uterine activity.

• Many factors increase likelihood of preterm delivery---Genetics, infection , malnutrition, behavior and environmental etc.

Myometrial Quiescence Maintained during Pregnancy—Till Phase -1 0f parturition

Genetics

Factors Responsible For Preterm Birth

>50% ARE IDIOPATHIC

>50%

25%

Genetic Influence on Preterm Labour

• Analogous to another disease processes , multiple co-existing genetic alterations and favorable environment for expression of genetic factor may lead to preterm labour.

• There is polymorphism in genes associated with inflammation and infection and in those with collagen turnover.

• Inherit ant mutation in genes regulating collagen assembly may produce cervical insufficiency-or Pre PROM.

Pre PROM(PPROM)This defines premature rupture of membranes before 37 weeks and

before onset of true labour.STRUCTURE OF THE FETAL MEMBRANES• The human amnion is composed of five distinct layers.• It contains no blood vessels or nerves; the nutrients it requires

are supplied by the amniotic fluid.• The innermost layer, nearest the fetus, is the amniotic

epithelium. Amniotic epithelial cells secrete collagen types III and IV and noncollagenous glycoproteins (laminin, nidogen, and fibronectin) that form the basement membrane, the next layer of the amnion.

• The compact layer of connective tissue adjacent to the basement membrane forms the main fibrous skeleton of the amnion.

Structure of Fetal membrane----• The collagens of the compact layer are secreted by mesenchymal

cells in the fibroblast layer.• Interstitial collagens (types I and III) predominate and form parallel

bundles that maintain the mechanical integrity of the amnion Collagen types V and VI form filamentous connections between the interstitial collagens and the epithelial basement membrane .

• The fibroblast layer is the thickest of the amniotic layers, consisting of mesenchymal cells and macrophages within an extracellular matrix.

• The collagens in this layer form a loose network with islands of noncollagenous glycoproteins.

• The intermediate layer (spongy layer, or zona spongiosa) lies between the amnion and the chorion. Its abundant content of hydrated proteoglycans and glycoproteins gives this layer its “spongy” appearance in histologic preparations, and it contains a non fibrilar meshwork of mostly type III collagen

Layer Extracellular-Matrix Composition MMP or TIMP Produced

AmnionEpthelium MMP-1, MMP-2,

MMP-9

Basement membrane Collagen types III, IV, V: laminin, fibronectin, nidogen

Compact layer Collagen types I, III, V, VI; fibronectin

Fibroblast layer Collagen types I, III, VI; nidogen laminin, fibronectin

Intermediate (spongy) layer Collagen type I, III, IV; proteglycans

Chorion

Reticular layer Collagen types, I, III, IV, V, VI; proteoglycans

Basement membrane Collagen types IV; fibronectin laminin

Trophoblasts MMP-9

: structure of the fetal membranes

Machanism of rupture of Membranes• Intrapartum rupture of the fetal membranes has been attributed to

generalized weakening due to uterine contractions and repeated stretching. The tensile strength of the membranes is reduced in specimens obtained after labour as compared with those obtained during caesarean delivery without labour

• Generalized weakness of the membranes has been more difficult to

establish when prematurely ruptured membranes have been compared with membranes that were artificially ruptured during labour

• Membranes that rupture prematurely, however, appear to be focally defective rather than generally weakened. The area near the rupture site has been described as a “restricted zone of extreme altered morphology” that is characterized by marked swelling and disruption of the fibrilar collagen network within the compact, fibroblast, and spongy layers ; Because this zone does not include the entire rupture site, it may appear before membrane rupture and represent the initial breakpoint.

CHANGES IN COLLAGEN CONTENT, STRUCTURE, AND CATABOLISM

• The maintenance of the tensile strength of fetal

membranes appears to involve an equilibrium between the synthesis and the degradation of the components of the extracellular matrix. It has been proposed that changes in the membranes, including decreased collagen content, altered collagen structure, and increased collagenolytic activity, are associated with premature rupture of the membranes.

Connective-Tissue Disorders and Nutritional Deficiencies as Risk Factors

• Although there are conflicting data regarding changes in the composition of fetal-membrane collagen in association with the length of gestation and membrane rupture, a decline in membrane collagen content or a change in collagen structure probably precedes rupture of the membranes.

• Connective-tissue disorders are associated with weakened fetal membranes and an increased incidence of preterm premature rupture of the membranes.

• Nutritional deficiencies that predispose women to abnormal collagen structure have also been associated with an increased risk of preterm premature rupture of the membranes. Collagen cross-links, which are formed in a series of reactions initiated by lysyl oxidase, increase the tensile strength of fibrilar collagens.

• Lysyl oxidase is produced by amniotic mesenchymal cells, which lay down the collagenous compact layer of the amnion. .

• Lysyl oxidase is a copper-dependent enzyme, and women with premature rupture of the membranes have lower copper concentrations in maternal and umbilical-cord serum than women whose fetal membranes are artificially ruptured during labour.

Increased Collagen DegradationThe degradation of collagen is mediated primarily by matrix metalloproteinases,

which are inhibited by specific tissue inhibitors and other protease inhibitors.The matrix metalloproteinases are a family of enzymes produced by various types

of cells that hydrolyze at least one component of the extracellular matrix. Because of the various substrate specificities of matrix metalloproteinases, effective catabolism of the many component molecules in the extracellular matrix requires the concerted actions of several enzymes.

The interstitial collagenases matrix metalloproteinase-1 (MMP-1) and MMP-8 cleave the triple helix of the fibrilar collagens (types I and III), which are then further degraded by the gelatinases MMP-2 and MMP-9.

These gelatinases also cleave type IV collagen, fibronectin, and proteoglycans. In human fetal membranes, MMP-1 and MMP-9 messenger

RNA and protein have been localized to amniotic epithelial cells and chorionic trophoblasts.

• Thus, the compact (collagenous) layer of the fetal membranes is sandwiched between two layers of cells that produce matrix metalloproteinases.

• Tissue inhibitors of metalloproteinases form 1:1 stoichiometric complexes with matrix metalloproteinases and inhibit their proteolytic activity. Tissue inhibitor of metalloproteinase-1 (TIMP-1) binds to activated MMP-1, MMP-8, and MMP-9, and TIMP- 2 binds to latent and active forms of MMP-2.

• The more recently described TIMP-3 and TIMP-4 appear to inhibit matrix metalloproteinases as efficiently as TIMP-1.Coordinated activities of matrix metalloproteinases and tissue inhibitors of matrix metalloproteinases are essential to the process of extracellular matrix remodelling.

• Near the time of delivery, however, the balance between activated matrix

metalloproteinase's and their tissue inhibitors shifts toward proteolysis degradation of the extracellular matrix of the fetal membranes.

• In human amnion and chorion, MMP-9 activity increases and TIMP-1 concentrations decrease dramatically with labour ;

• These changes may reflect a coordinated progression of events preceding and during parturition, resulting in the controlled degradation of collagen within the fetal membranes.

• Premature rupture of the membranes may also be caused by an imbalance

between the activities of matrix metalloproteinases and their tissue inhibitors, leading to inappropriate degradation of the membranes’ extracellular matrixes.

• Collagenase activity is increased in prematurely ruptured membranes at term. • Overall, protease activity is increased in membranes of women with preterm

premature rupture of the membranes, the predominant activity being that of MMP-9.

• Furthermore, gelatinolytic activity corresponding to latent and active forms of MMP-9 is increased and the concentration of TIMP-1 is low in amniotic fluid obtained from women whose pregnancies were complicated by preterm premature rupture of the membranes

Mechanism of PROM

Spontaneous Preterm labour• Pregnancies with intact membranes and spontaneous labor must be

distinguished from those complicated by PPROM.• Even so the Spontaneous preterm labour do not constitutes the

homogenous group characterized singularly by initiation of parturition.

• Among the most common associated findings are multiple pregnancy , Intra uterine infection, IUFD, IUGR, bleeding , placental infarction , premature cervical dilatation, cervical incompetence , uterine and fetal anomalies.

• Many forms of spontaneous preterm labour result from preterm initiation of 2nd phase of parturition although this is also questioned.

• Identification of common and uncommon factors has begun to explain the physiological process of human labour at term and preterm ----A, Uterine distension B. maternal—fetal risk ,C Infection.

A. Uterine over distension & Preterm labour• There is no doubt that multiple pregnancy and poly

hydroaminos – associated with over distension of uterus lead to preterm labour.

• It is likely that over distension of uterus acts to initiate early expression of contraction associated proteins ( CAP )in myometrium.

• The CAP genes influenced by stretch include those coding for gap junction proteins such as connexin43 for oxytocin receptors and PGs synthase.-- decrease uterine quiescence.

• Excessive myometrial stretch also initiate premature activation of placental—fetal endocrinal cascade ---early rise in CRH, increased Estriole and premature with drawl of progesterone.

• Early uterine stretch also play a role in premature onset of cervical remodeling --- cervical softening, ripening and dilatation.

Preterm stimulation of fetal –placental endocrine system

by uterine stretch

Maternal - fetal biological Stress Response

• There are plenty of evidences that maternal physical and psychological stress ( PIH, APH, Infection , Nutritional deficiency , anemia etc.)and fetal distress ( IUGR, IUFD, Placental infection/ infestation, multiparty, hydraminos etc,) initiates stimulate placental –adrenal endocrine axis provides a potential mechanism for initiation of preterm labour .

• Serial estimation of Rising levels of placental CRH and estriole in maternal circulation have been noted as an important precursor of predicting on set of preterm labour

Phenomenon --- explained in next flow chart

Maternal -fetal stress Increased Placental - CRH

Increased ACTH

Adult adrenal

fetal Adrenal

Production of steroids

Increased - fetal cortisol

Fetal Adrenal cortisol

DHEA-S biosynthesis

Abstract to increase production of Maternal Estriol

Decreased Uterine Quiescence

Decreased uterine quiescence- PTL

Intra uterine infection And Preterm Labour

• A great interested has generated in the role of intra uterine infection ---though intra amniotic culture studies have hardly demonstrated 10-40 % positivity for microbes.

• Microbes associate with preterm labour are– Gardenella Vaginalis , Fusobacterium , Micoplasm Hominis and Uroplasma urealyticum

• But subclinical intrauterine infection is not uncommon, has been promoted as the most common accompaniment and cause of preterm labour,

• Microbes entered in maternal tissue produce endo toxins -reach the amniotic cavity --- produce inflammatory response--- cytokinins in amnion –chorion.

• these cytokynins– initiate PGs synthesis --- cascade Of placental CRH – adrenal axis

Possible routes of

intra uterine infection

Inflammatory response to bacterial invasion --- Preterm labour

• Bacteria invasion -Endotoxins production Toll like receptor present or develop in de novo on invading Mononuclear phagocytes, Decidual , amniotic , trophoblast cells ---Legends –polysaccharides Increased release of chemokines , cytokines and PGs ---resulting switched on Cascade initiate myometrial contraction.

• Thus microbes may not invade the cells and amniotic cavity but there is Increased invasion of Inflammatory cells in decidua, myometrium , amnion and cervix.

• Myometrial cells produce –cytokines –IL-1-6-8 and TNF alpha.• Cervical stroma and glands ---IL-1-8 and TNF alpha .IL cytokines play a critical role in

cervical remodeling and dilatation.• Leukocytes infiltration in fetal membranes --- synthesis of chemokines ---Monocyte

Chemotactic protein( MCP-1). MCP-1 is more in fore water than hind water bag. • Mcp-1 infiltration amniotic cells PGs synthesis .• Infiltration of inflammatory cells in placenta --- Increased production of CRH

Placental – adrenal endocrine axis stimulation.

Summary of Preterm Labour--Machanism

• Preterm Labour is a pathological condition with multifactoral etiologies – now Termed As “Preterm Parturition Syndrome “.

• Role of intra uterine infection ( clinical / subclinical ) is an important and major mediator of Preterm birth .

• In recent years our understanding of other influences in parturition process, such as nutrition before and during pregnancy ,Genetic and dynamics regulating the process of remodeling the extra cellular matrix, have led to new awareness in this complicated and multifactoral process.

• Current and future application of genomic and bio informatics as well as microcellular biological studies will shed a new light on the pathways involved in term and preterm parturition

• These will help to identify ongoing process in all phases of cervical remodeling and myometrial activity.