Definition of Preterm :

Pre-term labour is defined as the presence of true labour (Regular painful uterine contractions associated with cervical effacement and dilatation) before the 37^th week of pregnancy and after the age of viability of the fetus.

Eg 37 weeks and 1 day is not preterm while 36 weeks and 6 days is preterm.

In the UK the age of viability is considered to be 24 completed weeks of gestation -from the date of the last menstrual period-LMP or 22 completed weeks from the date of conception, assuming a 28 day menstrual cycle.

The correct term for the onset of labour before 24 weeks of gestation is miscarriage rather than preterm labour.

Predisposing factors/ causes of pre-term labour:

Obstetric and gynaecological causes:

i) Previous history of preterm/ premature rupture of membranes

ii) Cervical incompetence

iii) Multiple Pregnancy

iv) Polyhydramnios.

v) Antepartum Haemorrhage.

vi) History of previous intrauterine death of the fetus.

vii) Uterine abnormalities

viii) Idiopathic

ix) Previous history of elective delivery due to preterm or intrauterine growth retardation.

x) Vaginal infections

Medical causes:

i) Heart disease and other medical disorders

ii) Systemic infections

iii) Anaemia (Hb< 9.5g/dl) and high haemoglobin concentration (> 13.5 g/dl) is associated with a markedly increased risk of preterm.

Epidemiological Causes:

i)Women from the lower socioeconomic class of society

ii)Body mass index (BMI) <19

iii)Young and older age mothers.

iv)Smoking mothers.

v) Single mother (Unmarried/unsupported).

What is preterm pre-labour rupture of membranes?

This is the pre-labour rupture of the membranes with subsequent preterm labour. The important and well know complication of preterm pre-labour rupture of membranes is ascending infection.

Preterm Pre-labour rupture of membranes will be discussed separately on another post.

Incidence and epidemiology:

Approximately 7% of labours are preterm.

The incidence of preterm is much higher among women from the lower socioeconomic class of society. It is also much lower among more affluent areas.

The period called term (Between 37 and 42 completed weeks of gestation) is the period where 90% of births occur. This explains the fact that the length of a normal human pregnancy is much more variable than other mammals.

Diagnosis of preterm:

Although the only real proof of preterm labour is the progressive dilatation of the cervix, the diagnosis of preterm labour has to be made on the basis of uterine contractions. This is because it is too late to try any preventive measures once cervical dilatation is established.

Some of the problems associated with the diagnosis of preterm labour are:

i) Bouts of preterm uterine contractions experienced by numerous women and which are not associated with progressive dilatation of the cervix and preterm delivery.

ii) Preterm labour can be easily confused with acute presentations of abdominal pain such as in urinary tract infection (UTI) and pre-eclampsia.

A thorough history and examination should be undertaken in any woman suspected to have preterm labour as it is a leading cause of neonatal mortality.

If there is any evidence of ruptured membranes, digital examination should be avoided , as it increases the risk of ascending infection. The examination should be repeated 4 hours later if thee is any doubt doubt about the diagnosis.

Cardiotocography is  very useful in the diagnosis of preterm labour. It also helps to confirm fetal wellbeing by observing the fetal heart rate pattern. However one has to note that the absence of uterine contractions does not eliminate the diagnosis of preterm labour. A vaginal examination is still necessary.

A high vaginal swab at the time of the speculum examination for Gram stain, microscopy and culture (look for group B streptococcus- most dangerous). This will enable the use of appropriate antibiotics if infection develops.

The management of preterm labour will be covered in a subsequent post.

Feel free to ask any questions/comments below

References:

i) Chapter 24 pages 291-294 Preterm Labour by P.J Steer -Dewhurst’s Textbook of Obstetrics and Gynaecology for Postgraduates, Sixth Edition. Edited by D. Keith Edmonds.

ii) Chapter 18 pages 273-275 Preterm Labour -Obstetrics by Ten Teachers- Seventeenth Edition edited by Stuart Campball and Christoph Lees.

It is also known as acute inversion of the uterus. It is a rare complication of the third stage of delivery. The incidence is about 1 in 2000 deliveries. It could be partially or completely turned inside out after delivery.

There is no evidence to suggest that acute uterine inversion is caused by the mismanagement of the third stage of labour.

Clinical features and diagnosis.

There is profound shock( Reduced perfusion to the peripheral areas of the body-ie a reduction in the flow of blood to the limbs and organs etc) which is out of proportion to the amount of blood loss. The vaginal tone is increased, a physiological response to acute inversion of the uterus.

The uterus may or may not protrude through the vagina. In over 90% of cases uterine inversion is associated with haemorrhage.

Degrees of Uterine Inversion

a) Inverted fundus reaches the cervical os.

b) The whole body of the uterus is inverted up to the vulva.

c) The uterus, vagina and cervix are completely inverted.

Principles of Management

The immediate resuscitation of the patient is of utmost importance, this is achieved by the treatment of hypovolemia (reduced amount of circulating blood volume).

If the inversion of the uterus occurs at the time of delivery one should try to replace the uterus back to the normal position manually with the hands immediately.

The earlier the restoration is done the more likely that it would succeed. One should not try to remove the adherent placenta without repositioning the uterus.

Once uterine inversion has occurred one should not attempt control cord traction and counter traction (Active management of labour).

The placenta should be removed manually (see the post on retained placenta and manual removal of the placenta.)

Procedure to replace immediately:

Immediate replacement of the inverted uterus via the vagina is recommended. The part which was inverted last should be replaced last, therefore the fundus must be replaced last.

Give atropine 0.6mg intravenously and diazepam 10mg iv.

After replacement of the uterus give ergometrine 0.5mg iv, then the placenta can be removed manually.

Procedure to replace the inverted uterus in the theatre:

The uterus of only about a third of patients can be repositioned without the use of uterine relaxants. This is best done under general anaesthesia using halothane (2% or higher).

Once the uterus is repositioned the attendants hand should remain in the uterine cavity until firm contraction occurs.

Once the procedure is completed, further bleeding and recurrence of inversion can be prevented by giving syntocinon infusion 20 units in 500ml of normal saline.

Procedure to replace the uterus if the inversion takes place sometimes after delivery:

O’ Sullivan’s hydration method of replacing the uterus should be tried.

In this method about 2 liters of normal saline in body temperature is instilled into the posterior fornix of the vagina (This can be done via a rubber tubing connected to a douche can or using an infusion set).

The douche can or the saline bag should be kept more than 1 meter above the patient. The escape of the fluids should be prevented by the operators hand blocking the introitus (opening of the Vagina) or by using several green armitage forceps. After the hydrostatic reduction is complete the fluid is allowed to flow out freely. The placenta can be manually removed if it is still attached.

0.5 mg of ergometrine or 10 units of oxytocin should be given after the procedure.

Reference:

O’ Sullivan JV (1945) Acute inversion of the uterus B med J 2 ,282.

Chapter 26: Obstetric Procedures by R Johanson. Dewhurst’s Textbook of Obstetrics and Gynaecology for Postgraduates. Sixth Edition Edited by Keith Edmonds.

The third stage of labour refers to the period from the birth of the baby to the complete delivery of the placenta and membranes. The third stage of labour is a crucial time in the management of labour.

Major complications such as retained placenta and primary postpartum haemorrhage could occur.

The third stage normally lasts between 5 and 10 minutes. The third stage is said to be prolonged if it is greater than 30 minutes.

The separation of the placenta from the uterus occurs in the third stage of labour . It occurs due to uterine contraction and retraction of the muscle fibers of the uterus, which leads to the formation of a cleavage plane within the deciduas basilis.

The Signs of Placental Separation are:

i) The fundus of the uterus rises up and also becomes hard and globular (rises up to the umbilicus).

ii) A gush of blood from the vagina.

iii) Lengthening of the cord.

The lengthening of the cord is the most convincing sign of placental separation. If a clamp is placed on the cord as close as possible to the vulva , the lengthening of the cord can be easily detected.

Management of the third stage of labour:

Active management of the third stage of labour is now recommended in modern obstetric practice. It reduces the incidence of post partum haemorrhage.

In active management there is no need to await signs of placental separation.

The active method of delivery is also known as Brandt Andrews method which is controlled cord traction (Traction and countertraction).

The active management of labour entails :

i) Intramuscular syntometrine (0.5 mg of ergometrine and 5iu of oxytocin) is given to the mother with the delivery of the anterior shoulder . Alternatively 10iu of synthetic oxytocin could be given. Syntometrine should not be given to hypertensive women.

ii) The cord should be clamped ( with two clamps) approximately 1 minute after the delivery of the baby. The lengthening of the cord is easily observed is a clamp is placed close to the vulva. The left hand of the delivery attendant (Midwife or Doctor) should feel the uterus for contraction while the right hand should grasp the cord. A steady traction should be exerted until the placenta is delivered.

Complications of the Third Stage of Labour

i) Primary postpartum haemorrhage.

ii) Retained placenta.

iii) Genital tract injuries.

iv) Acute inversion of the uterus.

v) Post partum shock and collapse.

Among the complications of the third stage of labour, primary post partum haemorrhage and retained placenta are the commonest complications.

The complications of the stage stage of labour will be dealt with extensively with posts dedicated to each complication.

References:

O’ Driscoll .K, Meagher D, Boylan P, Active Management of Labour, 3^rd Edition. Mosby 1993.

Russel .K.P (1982) The course and conduct of normal labour and delivery in current obstetric , gynaecologic diagnosis and treatment, 5t edition R.C. Benson. Lange Medical Publications, Los Altos , California.

Labour is divided into three stages

First Stage: This stage lasts from the onset of labour( When the woman begins to have regular painful uterine contractions) and a dilated cervix of 2-3 cm to a full cervical dilation of 10 cm.

The average duration of the first stage is about 12 to 14 hours for primigravida (woman who have not delivered before, ie first time delivery) . For women who have delivered before  (Multipara) this stage lasts about 8 to 10 hours.

Second Stage: The second stage starts at the time of full cervical dilatation and ends with the birth of the baby. The average duration of the second stage for a primigravida is about 25 minutes while for a multipara it lasts for about 15 minutes.

Third Stage: The third stage lasts from the time the baby is born to the time the placenta is delivered. The average duration of the third stage is about 5 minutes for the primigravida and 6 minutes for the multipara.

What is the average duration of labour?

In primigravida (woman who have not delivered before, ie first time delivery) the average total duration of labour is about 14 hours. While for a multipara (Women who have delivered before) the average total duration of labour is about 10 hours.

The components or essential factors of labour

The components or essential factors of labour are commonly referred to as the three P’s of  labour. These include:

i) The Passage: There are four types of pelvis, the gynecoid, android, anthropoid and platypelloid. The gynecoid pelvis is the normal female pelvis while the male type is referred to as the android. The pelvic inlet, the mid-cavity and the outlet should be carefully evaluated.

If the clinical pelvimetry is in doubt a lateral x-ray pelvimetry is very useful in assaying the bony pelvis. The soft tissue of the pelvis which includes the muscles, fascia and ligaments should also be assayed as excessive scarring can delay labour.

ii) The Powers: As labour progresses in normal labour the contractions become regular , stronger and well co-ordinated . They occur every 2 to 3 minutes (about 3 times per 10 minutes) . The intensity (force of contractions increases) from an average of 20 to 30 mmHg to 50 mmHg.

As the labour progresses the upper segment becomes thicker while the lower segment becomes thinner.

iii) The Passenger: The passenger refers to the baby. The average size babies tend to have the best prognosis (assuming that the baby does not have any congenital malformations/diseases) in terms of neonatal well being . 

The average size of the fetus at term(Birth weight) varies from country to country .eg in Sri Lanka the average birth weight is 2.8 Kg while in Nigeria it is 3.4 Kg.

References:

Dewhurst’s Textbook of Obstetrics and Gynaecology for Postgraduates (Sixth Edition)-Edited by Keith Edmonds FRCOG , FRACOG

Oxford Handbook of Clinical Specialties-6 th edition

Obstetrics by Ten Teachers- edited by Stuart Campbell and Ash Monga- 17th edition

Textbook of Obstetrics and Gynaecology for Medical Students by Akin Agboola et al-2nd edition

What is false labour (Braxton Hicks contractions)?

This refers to irregular weak uterine contractions which may occur before term or at term. They are usually not painful. Braxton Hicks contractions can cause a lot of anxiety and may even lead to premature admission to the labour ward.

How can I differentiate a false labour from a true labour?

The only definitive way to differentiate a false labour from a true labour is to get a vaginal examination (V/E) done by a midwife or a doctor. The vaginal examination will reveal  a dilated cervix and or effaced cervix.

In true labour there must be more than one contraction in 10 minutes. Contractions can either be recorded by modern instruments or by feeling the abdomen with the palm of the hand.False labour is usually not very painful and not forceful.

It must be emphasized that labour does not begin at a point, it is a gradual physiological transition from late pregnancy to labour.

What causes the onset of labour?

The mechanism responsible for the onset of labour is still not properly understood.

What is known is that prostaglandin hormones are primarily responsible for stimulating uterine contractions of labour . It is believed that prostaglandin action on the uterus is mainly due to cervical ripening rather than stimulating uterine contractions. Cytokines, oxytocin ,steroid hormones, endothelin-1 and platelet activating factor (PAF) may stimulate prostaglandin synthesis ,while progesterone and phospholipase A2 inhibitors may inhibit prostaglandin synthesis.

A fall in plasma progesterone has also been observed prior to the onset of labour. Even though oxytocin stimulates uterine contractions , its concentration in the blood does not rise near term. Relaxin, is another hormone that is thought to help cervical ripening.

Prostaglandins and oxytocin may increase intracellular free calcium ions which in turn causes contractions by formation of the contractile entity of  actin-phosphorylated myosin.

Uterine contractions are involuntary in nature . There is little or no neuronal control over uterine contractions.

The duration of pregnancy is also affected by the fetal genotype.

There is progressive shortening of the uterine smooth muscles as labour progresses .This is called retraction . Retraction mainly takes place in the upper segment of the uterus. After contractions they do not return to their original size. This enables the lower segment to become thinner and more stretched, eventually the cervix also becomes stretched and taken up into the lower segment of the uterus.

References:

Dewhurst’s Textbook of Obstetrics and Gynaecology for Postgraduates (Sixth Edition)-Edited by Keith Edmonds FRCOG , FRACOG

Oxford Handbook of Clinical Specialties-6 th edition

Obstetrics by Ten Teachers- edited by Stuart Campbell and Ash Monga- 17th edition

Textbook of Obstetrics and Gynaecology for Medical Students by Akin Agboola et al-2nd edition