Bio activity of Preterm Labour
Prof. M.C. Bansal.
MBBS. MS. MJCOG. FICOG.
Founder Principal& Controller;
Jhalawar Medical College And Hospital
Ex. Principal & Controller;
Mahatma Gandhi Medical College And
Hospital, Sitapura , Jaipur.
• 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
• Preterm Birth carry major adverse risks of human
• 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
Myometrial Quiescence Maintained during
Pregnancy—Till Phase -1 0f parturition
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
• Inherit ant mutation in genes regulating collagen
assembly may produce cervical insufficiency-or
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
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
• The fibroblast layer is the thickest of the amniotic layers,
consisting of mesenchymal cells and macrophages within an
• 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
: structure of the fetal membranes
MMP or TIMP Produced
Collagen types III,
Collagen types I, III, V, VI; fibronectin
Collagen types I, III, VI; nidogen laminin,
Intermediate (spongy) layer
Collagen type I, III, IV; proteglycans
Collagen types IV; fibronectin laminin
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
• 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
• 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 Degradation
The 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
• Thus, the compact (collagenous) layer of the fetal membranes is
sandwiched between two layers of cells that produce matrix
• 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
• 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’
• Collagenase activity is increased in prematurely ruptured membranes at
• 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
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
• 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
• Early uterine stretch also play a role in premature onset of
cervical remodeling --- cervical softening, ripening and
Preterm stimulation of fetal
–placental endocrine system
by uterine stretch
Maternal - fetal biological Stress
• 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
Phenomenon --- explained in next flow chart
Maternal -fetal stress
of Maternal Estriol
Production of steroids
Increased - fetal
Intra uterine infection And Preterm
• 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
• 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
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
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
• 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.
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