Preterm Labor (Syn: Premature Labor)

Question 1

What is preterm labour?

Answer 1

Preterm labor (PTL) is defined as labor that spontaneous occur before the 37th completed week (< 259 days)
 Lower limit of GA is not uniformly defined; age of viability is 24 weeks in developed countries, and 28 weeks in
resource limited settings

Preterm labor is defined as labor
(contractions with cervical
dilation) occurring before 37
completed weeks.

Question 2

High risk factor for prterm labour

Answer 2

a) Incidence of preterm labor is Increased in Previous history of;
 Induced or spontaneous abortion or preterm delivery
 Pregnancy following assisted reproductive techniques (ART)
 Asymptomatic bacteriuria or recurrent urinary tract infection
 Smoking habits - two-fold increase of PPROM
 Extremes of maternal age- Age < 18 or > 40 years
 Low socioeconomic and nutritional status
 Maternal stress.
 Drugs of abuse: especially cocaine
 Body mass index (BMI) <20: underweight women
b) Pregnancy complications: maternal, fetal or placental.
i) Maternal: Pregnancy complications:
 Preeclampsia,
 Antepartum hemorrhage
 Premature rupture of the membranes,
 Polyhydramnios
 Multiple pregnancy,
 Uterine anomalies: Cervical incompetence, malformation of uterus, fibroids
 Medical and surgical illness: Acute fever, acute pyelonephritis, diarrhea, acute appendicitis, toxoplasmosis
and abdominal operation.
 Chronic diseases: Hypertension, nephritis, diabetes, decompensated heart lesion, severe anemia, low body
mass index (LBMI) and Genital tract infection, Bacterial vaginosis, beta-hemolytic streptococcus,
bacteroides, chlamydia, and mycoplasma.
ii) iii) iv) Fetal: congenital malformations, intrauterine death., IUGR
Placental: Infarction, thrombosis, placenta previa or abruption.
Idiopathic: (Majority)- often associated with Premature effacement of the cervix with irritable uterus and
early engagement of the head

Question 3

Clinical features of preterm labour

Answer 3

Confirm GA by reviewing menstrual history, HOF and any prior ultrasound to establish gestations viability.
 Presence of symptoms of early labour;
 Regular uterine contractions,
 cervical effacement and dilatation,
 membrane rupture,
 Funneling of the internal os,
 Pelvic pressure, Backache and or
 vaginal discharge or bleeding
 Speculum examination may reveal; pooling of amniotic fluid, bld and/ or abnormal discharge, cervical dilatation
 Assess vitals: pulse, blood pressure, temperature and state of hydration- i. maternal tachycardia, ii. Fetal
tachycardia, iii. Fever and iv. Uterine tenderness

Question 4

Diagnosis of preterm labor

Answer 4

Preterm labor is based on the following criteria in patients with ruptured or intact membranes:
1. Documented uterine contractions (4 per 20 minutes or 8 per 60 minutes)
2. Documented cervical change (cervical effacement of 80% or cervical dilation of 2 cm or more).
NB: Uterine contractions are not a good predictor of preterm labor, but cervical changes

Question 5

Predictors of preterm labor:

Answer 5

A. Clinical predictors:
i) Multiple pregnancy
ii) History of preterm birth
iii) Presence of genital tract infection
iv) Symptoms of PTL.
B. Biophysical predictors:
i) Uterine contractions (UC) > 4/hr
ii) Bishop score > 4
iii) Cervical length (TVS) < 25 mm.
C. Biochemical predictors:
i) Fetal fibronectin (fFN) in cervico vaginal discharge (see below)
ii) Others IL-6, IL-8, TNF-a

Question 6

Differential diagnosis of preterm labour

Answer 6

1. Urinary tract infection
2. Red degeneration of fibroid
3. Placental abruption
4. Constipation
5. Gastroenteritis

Question 7

Investigations for preterm labour

Answer 7

1. Full blood count
2. Serum electrolytes and glucose levels when tocolytic agents are to be used
3. LFT, U/E + Creat
4. Urine for routine analysis, microscopy, culture and sensitivity;
5. Cervicovaginal swab for culture
6. Cervicovaginal swab for fibronectin (fFN). Fetal fibronectin is a ‘glue-like’ protein binding
   the choriodecidual membranes. Any disruption at the choriodecidual interface results in fFN release
7. 8. Cardiotocograph (CTG)- to determine the status of the fetus
      Ultrasonography for fetal well being, EFW, fetal presentation, cervical length (normal cervix measures approx
      35 mm) and placental localization. Significant cervical shortening is often accompanied by dilatation and
      funnelling of the membranes down the cervical canal
8. Vaginal examination- Repeat V/E 1–4 hours in the absence of specialized tests or interval is guided by
   the severity of symptoms

Question 8

Management of Mothers with risk/s factors for preterm labour

Answer 8

Mothers with risk/s factors for preterm labour should;
a) Receive Glucocorticoids to reduce neonatal RDS, IVH and NEC. 2 doses of betamethasone or 4 doses of
dexamethasone (48 hours to complete dosing)
b) c) d) e) f) g) Be transfered antenatally to an equipped center with NICU services
Recieve tocolytic drugs for a short period unless contraindicated.
Receive antibiotics to prevent neonatal infection with Group B Streptococcus (GBS)
Carefully be monitored intrapartumly and insure minimal trauma
Seek the presence of a neonatologist during delivery
Prefer vaginal delivery, unless otherwise indicated for cesarean birth

Question 9

Management of preterm labour

Answer 9

Benefits of in utero existence are weighed against the risks of threatened preterm delivery and in each case a
decision is reached about the best treatment options.
 Bed rest to prevent early rupture of the membranes
 Place pt in the lateral decubitus position to take the uterine weight off the great vessels
 Give glucocorticoids for fetal pulmonary maturation to reduce mortality and incidence of RDS, NEC and IVH in
preterm infants- GA (24 to 34 weeks); 2 doses of 12 mg of betamethasone, iv/im od, or 4 doses of 6 mg of
dexamethasone iv Bd.
 Evaluated for presence of any underlying correctable problem, such as UTI or vaginal infection.
 Ensure adequate fetal oxygenation by giving oxygen mother by mask
 Ensure oral or parenteral hydration- consider clear caloric liquids
 Cervical colonization and vaginal infection play critical role to etiology of preterm labor and PROM, obtain
cultures for group B Streptococcus. Other important organisms are Ureaplasma, Mycoplasma, and Gardnerella
vaginalis (these cause bacterial vaginosis)
 Administer antibiotics to patients in preterm labor
 Epidural analgesia is of choice,
 Labor should be carefully monitored prefer-ably with continuous EFM
 judged appropriate to hasten delivery, either because a late miscarriage appears inevitable or because the
maternal or fetal risks of continuing the pregnancy are judged too high
2nd stage:
 its extremely important to continue monitoring fetal heart and give prompt attention to abnormal fetal heart rate
patterns;
 Acidosis at birth adversely affects respiratory function by destroying surfactant and delaying its release.
 Birth should be gentle and slow to avoid rapid compression and decompression of the head
 Episiotomy may be done to minimize head compression if there is perineal resistance
 Cord is to be clamped immediately at birth to prevent hypervolemia and hyperbilirubinemia
 Shift baby to neonatal intensive care unit under the care of a neonatologist
 Place of cesarean section: Preterm fetuses before 34 weeks presented by breech are generally delivered by
cesarean section.

Question 10

Attepmts to arrest preterm labor

Answer 10

Attepmts to arrest preterm labor
 Bed rest- lie preferably in left lateral position.
 Adequate hydration is maintained.
 Prophylactic antibiotic- not given routinely but recommended when infection is evident.
 Prophylactic cervical circlage- in those with prior preterm birth and short cervix in present pregnancy.
 Tocolytic agents:

Question 11

Tocolytic agents in preterm labour

Answer 11

Tocolytic agents: including
i) Micronized progesterone 200mcg od-to inhibit uterine contractions.
ii) Betamimetics- terbutaline 0.25 mg SC injection of 0.25 mg every 3 to 4 hours is given
MOA: Activates intracellular enzymes (adenylate cyclase, cAMP, Protein kinase), thereby reducing
intracellular free calcium and inhibits activation of MLCK → Reduced interaction of actin and myosin →
smooth muscle relaxation. β (β2) receptor stimulation causes smooth muscle relaxation
iii) Nifedipine 10-20 mg every 3-6 hour
MOA; blocks the entry of calcium inside the cell.
iv) v) vi) Magnesium sulphate- Loading dose 4-6 g IV (10- 20% soln) over 20-30min followed by an infusion of 1-2
g/hr → to continue tocolysis for 12 hrs after the contractions have stopped.
MOA: competitive inhibition to calcium ion either at the motor end plate at the cell membrane reducing
calcium influx. Decreases acetylcholine release and its sensitivity at the motor end plate. Direct depressant
action on uterine
Oxytocin antagonists (Atosiban IV infusion 300 mg/min. a bolus may be needed
MOA: blocks myometrial oxytocin receptors. It inhibits intracellular calcium release, release of PGS and
thereby inhibits myometrial contractions
Nitric oxide (NO) Donors (Glyceryl trinitrate (GTN) Patches, isosorbid nitrate
MOA: Smooth muscle relaxant

Question 12

Contraindications for tocolytics

Answer 12

a. Advanced labor
b. Mature fetus (tocolysis rarely used after 34 weeks or after corticosteroids completed)
c. Intrauterine infection
d. Significant vaginal bleeding
e. Severe preeclampsia

Question 13

Prevention of PTL

Answer 13

1. 2. 3. Primary care- aimed to reduce incidence of preterm labor by reducing high-risk factors (e.g. infection, etc.).
         Secondary care - includes screening tests for early detection and prophylactic treatment (e.g. tocolytics).
         Tertiary care- aimed to reduce perinatal morbidity and mortality after diagnosis (e.g. use of corticosteroids).

Question 14

Explain the pathogenic causes of preterm labour

Answer 14

 There are 4 major causes:
 Stress
 Inflammation
 Placental abruption
 Abnormality in uterine
distension
STRESS
 Includes both physical and
emotional stress.
 The stress activates the
hypothalamic-pituitary-adrenal
axis in the mother.
 When the axis is activated the
stress hormones active preterm
labor.
 If the fetus undergoes stress this
also exacerbates the occurrence
of preterm labor.
INFLAMMATION
 May be as a result of an
inflammatory condition or
infection (urinary tract infection,
infection of fetal membrane,
dental infection)
 Bacteria can also produce
enzymes which can degrade the
fetal membranes and induce
labor.
PLACENTAL ABRUPTION
 In response to bleeding between
the placenta and the uterine wall, the uterus contracts to clump the
blood vessels in order to arrest
the bleeding.
 This contraction results in
induction of labor.
ABNORMALITY IN
UTERINE DISTENSION
 The uterus is more distended than
it should be for the specific
gestational age.
 The stretching of the
myometrium triggers preterm
labor (through release of
prostaglandins)
 Causes: multiple gestation,
polyhydramnios, abnormalities
with the cervix (Cervical
incompetence)