• Obstetrics and Gynaecology
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Preterm labour: Symptoms, Causes, Diagnosis and Treatment

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  • Revised on: 2020-10-20

Preterm labour is the presence of uterine contractions of sufficient frequency and intensity to cause progressive cervical effacement and dilatation occurring after 20 weeks' or but before 37 weeks' gestation regardless of birth weight.

This is because most of these babies are appropriately grown, some are small for gestational age and a small number are LGA.

A pregnancy normally lasts about 40 weeks and in a normal labor, more than 4 contractions an hour are needed to cause cervical dilatation.

For this diagnosis there must be appreciable cervical effacement or dilation of at least 2 cm without previous examination.

The uterine contractions need not be painful to cause cervical change and may manifest themselves as abdominal tightening, lower back pain, or pelvic pressure

Preterm labour is the major cause of neonatal morbidity and mortality and causes 25% of neonatal deaths that are not due to congenital anomalies in about 10-15% of all pregnancies.

Causes

Although the exact cause remains elusive triggers of preterm labour maybe multifactoral.

These causes are classified into those labours that commence spontaneously and elective causes where a decision is made to terminate a viable pregnancy before term.

Spontaneous causes

  • Up to 40% of the cases have unknown causes
  • Multiple gestation – the higher the multiple the greater the chance
  • High fevers or hyperpyrexia due to viral or bacterial infection,often urinary tract infections especially Pyelonephritis
  • Premature rupture of the membranes as a result of maternal infection, especially chorioamnionitis.
  • Maternal infections such as chorioamnionitis
  • Polyhydramnios
  • Maternal short stature,
  • Age (mothers who are less than 18 years and the ones over 35years of age,
  • Parity
  • Maternal uterine malformation most commonly often bicornuate or significant fibroids
  • Mothers with poor obstetric history such as history of preterm labour are at a higher risk
  • Mothers with cervical incompetense or ones with a history of cone biopsy
  • Substance abuse during pregnancy such as alcohol or cigarette smoking.

Elective causes

  • Elective or induced causes of preterm labour are:
  • Hypertensive disorders in pregnancy such as pregnancy-induced hypertension, pre-eclampsia, chronic hypertension
  • Maternal disease like renal, heart complications,
  • Placental abnormalities such as placenta praevia, abruptio placenta,
  • Rhesus incompatibility in rhesus negative mothers,
  • Fetal disorders such as congenital abnormality of the baby,and
  • Thyrotoxicosis in the fetus can lead to preterm labour,
  • Intrauterine growth restriction (IUGR).

Risk factors associated with preterm labor.

a) Obstetric complications

  • In previous or current pregnancy

Severe hypertensive states, anatomic disorders of the placenta, Placental insufficiency, Premature rupture of membranes, Polyhydramnios or oligohydramnios

  • Previous premature or low-birth-weight infant
  • Low socioeconomic status
  • Short interval between pregnancies (< 3 months)
  • Maternal age < 18 years or > 40 years
  • Low prepregnancy weight
  • Multiple pregnancy
  • Previous abortion
  • Non-Caucasian race
  • Inadequate or excessive weight gain during pregnancy
  • Previous laceration of cervix or uterus

b) Medical complications

  • Pulmonary or systemic hypertension
  • Renal disease
  • Heart disease
  • Infection:  acute maternal systemic infection, urinary tract infection, genital tract infection , feto-toxic infection, maternal intra-abdominal
  • Cigarette smoking and alcoholism,
  • Severe anemia
  • Malnutrition or obesity
  • Leaking benign cystic teratoma
  • Perforated gastric or duodenal ulcer
  • Adnexal torsion
  • Maternal trauma or burns
  • Positive foetal fibrinectin

c) Surgical complications

  • Any intra-abdominal procedure
  • Conization of cervix
  • Previous incision in uterus or cervix such as cesarean delivery)
  • Genital tract anomalies
  • Uterine abnomalities
  • Congenital cervical incompetency

Signs and symptoms of preterm labour

  1. Uterine contractions

Regular uterine contractions at frequent intervals, generally more than two in one-half hour.

  1. Dilatation and effacement of cervix

A cervical change in dilation or effacement of at least 1 cm or a cervix that is well-effaced and dilated at least 2 cm on admission is considered diagnostic.

  1. Vaginal bleeding

Most mothers present with bloody mucous vaginal discharge known as bloody show.

If the vaginal bleeding much significant, then the mother should be assessed for abruptio placentae or placenta previa.

Signs of preterm labour

Indicative signs of preterm labour are:

  • Show that may be blood stained
  • Palpable uterine activity
  • Engagement of presenting part
  • Cervical dilatation and effacement
  • Bulging membranes
  • Rupture of membranes

Diagnostic Investigations

The basic laboratory investigations done in cases where preterm labour is suspected are;

Blood slide for malaria parasites is the mother is from a malarial endemic region.

Urine sample may also be taken for microscopy culture and sensitivity

Swabs that may be obtained are:

  • High vaginal swab for gram stain and culture
  • Endocervical swab for gonorrhoea culture
  • Endocervical swab for Chlamydia

If genital infection is suspected, a urethral and anorectal swabs are indicated as well

If preterm labour is suspected then its prudent to take a vaginal fetal fibronectin before pelvic cervical examination.

Other investigations are usually ordered as per individual assessment

Ultrasound for foetal assessment and biophysical profiling (dating, foetal anomalies, presentation, liquor assessment, estimating foetal weight)

Treatment of preterm labour

The patient diagnosed with preterm labor should be observed for 30-60 minutes to determine appropriate management.

Decisions regarding management are made based on estimated gestational age

Management of these mothers falls into one of two categories:

  1. Expectant management (observation) or
  2. Active management

Goals of management

The goals of the management of preterm labour are;

  1. To identify the risk factors early
  2. To timely diagnose preterm labour
  3. To identify the cause
  4. To evaluate fetal well being
  5. To provide appropriate prophylactic measures
  6. To initiate tocolysis
  7. To establish fetal and maternal surveilance

Conservative management

Conservative management is done if the cervix less than 2 cm dilated and includes;

  • Bed rest if less than 34 weeks gestationshould be encouraged, especially where the mother has any of the conditions that predispose to preterm labour
  • Use of sedatives during preterm labour to ensure complete bed rest
  • Administration of tocolytics and
  • Use of corticosteroids preferably dexamethasone and bethametasone.
  • Treat underlying cause
  • Avoidance of strenuous exercise and calming the mother, because any strain or stress may aggravate preterm labour

Active management

Active Management is recommended if the cervical dilatation is more than 2cm, presence of foetal distress, or IUFT.

This type of management involves:

  • Use of corticosteroids in anticipation of preterm delivery.
  • Administration of antibiotics
  • Rupture the membranes nut not in the cases of IUFD,
  • Monitoring of labour and caesarean section is sometimes indicated for obstetric reasons, but vaginal delivery is usually preferable.

Hydration and Bed Rest

Hydration and bed rest should be started immediately upon presentation.

Corticosteroids

The administration of corticosteroids to accelerate fetal lung maturity

Steroids can be given according to one of two protocols:

  • Betamethasone 12 mg IM every 24 hours for a total of 2 doses; or
  • Dexamethasone 6 mg IM every 12 hours for a total of 4 dosesto improve foetal lung maturity and chances of neonatal survival.

This corticosteroid should not be used in the presence of frank Infection.

In pregnancies which are between 24 and 34 weeks' gestation or estimated fetal weight (EFW) between 600 and 2500 g, intervention with corticosteroids and tocolysis is recommended.

Fetuses of very preterm pregnancies, 20-24 weeks EGA or EFW less than 600 g, re not considered to be viable. If these pregnancies can be continued for several more weeks, the fetuses will become viable, but they have a high risk of significant morbidity if they survive.

Use of tocolytics

Tocolytics are to be initiated if the patient continues to experience contractions despite of hydration and bed rest.

The primary reason why these drugs are used is to prolong delivery for 48 hours so as the fetus sh


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