Preterm Labour
Type to enter a caption.
Introduction and Causes
By Humna Anis
Definition
• Preterm labour is defined by WHO as Onset of
Labour prior to the completion of 37 weeks of
gestation, in a pregnancy beyond 20 weeks of
gestation.
• Preterm labour is considered to be established if
regular uterine contractions can be documented
atleast 4 in 20 minutes or 8 in 60 minutes with
progressive change in the cervical score in the
form of effacement of 80% or more and cervical
dilation>1 cm.
• If uterine contractions are perceived in the
absence of cervical change, the condition is
called “Threatened Preterm Labour”.
• Nearly 50-60% of preterm births occur following
spontaneous labour.
• 30% due to preterm premature rupture of
membranes.
• Rest are iatrogenic terminations for maternal or
fetal benefit.
Pathogenesis
• Preterm labour maybe Physiological or Pathological.
• As parturition nears, the fetal adrenal axis becomes more sensitive
to ACTH and there is an increased production of Cortisol.
This stimulates 17-hydroxylase in the trophoblast resulting in
decreased progesterone secretion.
The reversal of estrogen-progesterone ratio
Increase in Prostaglandin Formation
Initiation of Labour
Classification
• For reasons related to aetiology, outcome and
recurrence risk, preterm births should be divided
into 3 gestational periods:
• Mildly preterm births (32+0 to 36+6 weeks)
• Very Preterm births (28+0 to 31+6 weeks)
• Extremely preterm births (24+0 to 27+6
weeks)
Aetiology and Risk Factors
• Obstetric Complications
• Racial Factors
• Demographic Factors
• Psychological Factors
• Past Obstetric History
• Infection
• Genetic Factors
Obstetric Risk Factors
• Conditions that cause over distension of uterus: Multiple
Pregnancies, Hydramnios.
• Preterm Premature Rupture of Membranes (PPROM)
• Idiopathic Preterm Labour
• Pre eclampsia
• Antepartum Hemorrhage
• Second Trimester bleeding not associated with Placental Causes
• Iatrogenic Preterm Termination for pre-eclampsia, fetal distress,
IUGR, Abruptio Placenta and uterine fetal death.
Racial Factors
• Black women have twice the risk compared to
whites.
This maybe explained by multiple factors like
socioeconomic status, medical disorders and
genetic predisposition.
Demographic Factors
• Women with low BMI and poor maternal weight gain in
pregnancy are at increased risk.
• Age-women younger than 17 and older than 35 yrs.
• Poor education
• Women living alone
• Minimal or no prenatal care
• Low socioeconomic status
• Multiple sexual partners
Psychsocial Factors
• Anxiety
• Stress
• Depression
• Negative life events
• Perception of racial discrimination and domestic violence
• Excessive alcohol intake
• Smoking
Past Obstetric History
• Previous h/o preterm birth (17-20% recurrence risk) or
second trimester pregnancy loss.
• 3 or more abortions (may result in cervical
incompetence)
• DES (diethylstilbestrol) exposure
• Conceptions following IVF
• Cervical incompetence (10-20% second trimester
losses)
Infection
• Result in 50% spontaneous preterm births.
• Asymptomatic bacterial vaginosis
• Trichomonas vaginalis
• Chlamydia trachoma’s
• Ureaplasma Urealyticum
• Mycoplasma hominis
• Asymptomatic bacteriuria
• Systemic Infections like pyelonephritis, pneumonia, acute
appendicitis.
Genetic
• Important component of idiopathic group.
• Single gene polymorphisms of cytokines in
both mother and fetus may be responsible.
• Polymorphisms involving TNF alpha-308, IL-
1Beta and IL-6 have been most consistently
associated with spontaneous preterm labour
and preterm birth.
Clinical Features of Preterm
Labour
• HISTORY:
• Always check the dating of pregnancy by
reviewing menstrual history and prior USG
examinations.
• Vague complaints such as increased discharge,
pelvic pressure or low backache.
• Contractions accompanied by advanced dilation
(>3cm), ruptured membranes or significant
vaginal bleeding.
• EXAMINATION:
• Abdominal examination will reveal the
presence of uterine tenderness, suggesting
abruption or chorioamnionitis.
• Speculum examination may reveal: pooling
of amniotic fluid, blood and/or abnormal
discharge.
• A visual assessment of cervical dilation.
Prediction of Preterm Labour
(Investigations)
• The two most promising markers currently
available are:
1.Fetal Fibronectin levels
2.Ultrasound assessment of cervical length
Fetal Fibronectin (fFN)
• It is an extracellular glycoprotein secreted by the chorionic tissue at
maternal-fetal interface.
• It is present in amniotic fluid, placental tissue and decidua basalis.It
acts as a biological glue which binds blastocyst to endometrium.
• It can be normally present upto 20-22 weeks.
• Therefore presence of fFN between 27-34 weeks can provide
important marker of preterm labour.
• Swabs can be taken from ectocervix or post vaginal fornix. ELISA
with FDC-6 monoclonal Ab is used to detect fFN.
• A cut-off of 50ng/ml is considered positive.
Length of Cervix
• Cervical insufficiency is defined as cervical
changes in absence of uterine contractions.
• Cervix can be assessed visually or by USG.
• A reduction in cervical length of >6mm between
2 Ultrasounds have higher risk.
• Funneling (internal os diameter >= 5mm) is also
independent risk factor.
Repeat Vaginal
Examination
• Repeat in 1-4 hours should be considered
essential in the absence of specialised tests. The
interval between assessments should be guided
by the severity of the symptoms.
