Post-dated Pregnancy &

Induction Of Labor

Post-term Pregnancy (Syn:Post-dated Pregnancy or Post maturity

Prolonged pregnancy)

• A pregnancy that has reached or surpassed 42 weeks ( 294 days ) of gestation from the first day of the last menstrual period. ( ACOG,WHO,FIGO)

• Incidence- Range 4-19%,Average incidence-10%

Aetiology

• Wrong dates- The most common cause of prolonged pregnancy, due to inaccurate LMP

• Hereditary- postdatism seems to run in families, showing a genetic predisposition

• H/o previous prolonged pregnancy- recurrence 50%

• Abnormal fetal HPA and adrenal hypoplasia as in anencephaly deficiency of dehydro-

epiandrosterone reduced fetal cortisol response.

• Placental Salphatase deficiency- this enzyme play a

critical role in synthesis of placental estrogens which are necessary for the expression of oxytocin & PG receptors in myometrial cells

Changes associated with prolonged pregnancy

• A series of changes occur in -amniotic fluid -placenta and - fetus

Amniotic Fluid Changes• In Postdated Pregnancy quantitative &qalitative changes occur in Amniotic fluid

Quantitative Amniotic Fluid Changes• Amniotic fluid peak 38wks ---- 1000ml 40wks ---- 800ml 42wks ---- 480ml 43wks ---- 250ml 44wks ---- 160ml• After 42wks there is 33% decrease in amniotic fluid volume/wk • A decrease in fetal renal blood flow is associated with postdatism

is the cause of oligohydromnios

• Amniotic fluid less than 400ml is associated with fetal complications

Method to evaluate amniotic fluid volume

• Most popular method to evaluate amniotic fluid volume is four quadrant technique to calculate Amniotic Fluid Index (AFI).

• AFI is obtained by measuring the vertical diameter of largest pocket of amniotic fluid in 4 quadrants of uterus by USG and the sum of the result is AFI

• AFI <5cm – oligohydromnios 5 – 10cm – decreased amniotic fluid volume 10 – 15cm – Normal 16 – 20cm – Increased amniotic fluid volume >25cm - Polyhydromnios

Qualitative Changes in Amniotic fluid • AF become milky and cloudy because of presence of

abundant flakes of vernix caseosa.

• The Phospholipids composition changes due to presence of large number of lamellar bodies released from fetal lungs. Vernix raises the lecithin, Sphingomyelin ratio to 4: 1 & more

• The liquor may be meconium stained as a result of intrauterine hypoxia

Placental Changes

• USG findings: -Indentation in chorionic plate become more marked,

giving the appearance of cotyledons

- Increased confluency of the comma- like densities that become the inter cotyledonary septations

- Appearance of hemorrhagic infarct & Calcification

Fetal Changes

• The fetus grow in utero after term - macrosomic which lead to fetopelvic disproportion , Prolong labor

Shoulder dystosia

• After term the fetus loses Vernix caseosa causing wrinkling of the skin due to direct contact with aqueous amniotic fluid

• Growth of hair and nails• Wasting of subcutaneous tissue

Diagnosis of Postdated Pregnancy

• The diagnostic accuracy of post term pregnancy hinges on the reliability of gestational age

• We can get accurate EDD by:-

- LMP when >3 normal regular period before LMP & no ocp

- EDD calculated by LMP coincide with EDD from USG

perform between 12-20wks

- When LMP not known EDD established from USG

between 7-11wks

- EDD corresponds to 36wks since the patient had +ve upt

- A reliable P/V finding for GA age in 1st trimester

Management• Prior to deciding any line of action it is important to

establish the diagnosis of post term gestation by history , examination and USG.

• Fetal Surveillance by – NST

- AFI

- Biophysical Profile

- Doppler ( Facilities available)

• Patient with Prolonged Pregnancy (>40wks) who need to be delivered :

* Women with medical or obstetrical complications

of pregnancy

* Favorable Cervix Bishop Score > 8

* Women with oligohydromnios

* Estimated fetal weight > 4.5kg

* Suspected fetal compromise

* Fetal congenital anomaly

* Hyper mature Placenta

• Expectant management of prolonged pregnancy is justified only when:

- GA <41 wks with unripe cervix, normal AFI ,

normal size baby , normal BPP and reactive

NST• There is universal agreement that once pregnancy

reaches 42wks delivery mandatory – Induction/ CS

-If there is signs of fetal distress ,wt. is > 4.5kg.or

obstetrical complicated pregnancy- CS

Complication of Postdated pregnancy

Maternal – Increased morbidity due to increased

Instrumental & operative delivery

Fetal - Intrapartum fetal distress

- MAS

- Fetal trauma due to macrosomia

- Increased Perinatal morbidity & mortality

INDUCTION OF LABOUR

• Induction Initiation or stimulation of uterine contractions before the spontaneous onset of labour with or without ruptured membranes

• Augmentation – refers to stimulation of uterine contractions that are already present but found to be inadequate.

Indications

Obstetrical indication• Post term pregnancy• Severe pre eclampsia/ eclampsia• PROM• Ruptured membrane with chorioamniotis• Intrauterine death• Fetal growth restriction• Nonreassuring fetal testing

• Rh iso-immunization• Malformed fetus• Abruptio Planctae• Severe hydramnios

Medical indication• Chronic nephritis/ renal disease• Chronic Hypertension• Diabetes

Contraindication

• Fetal macrosomia• Multifetal gestation• Malpresentation • Prior classical caesarean• Contracted pelvis• Major degree placenta previa• Active genital herpes infection• Cervical cancer

PREREQUISITES

Prior to initiation of induction the following should be assessed

• indication for induction/any contraindications• gestational age

• cervical favourability (Bishop score assessment)• assessment of pelvis and fetal size/presentation

• membrane status (intact or ruptured)• fetal well being/fetal heart rate monitoring prior to labour

Induction

• documentation of discussion with the patient including indication for induction and disclosure of risk factors

CERVICAL RIPENING PRIOR TO INDUCTION

• Cervical ripening is a component of induction of labor employed when the cervix is unfavorable in order to facilitate dilatation when labor is established.

Bishop’s Score (Modified)

Parameters Score

Cervix 0 1 2 3

Dilatation (Cm) Closed 1-2 3-4 5+

Effacement(%) Or Cervical Length (Cm)

0-30 Or >4

40-50 or 2-4

60-70 or 1-2

≥ 80 or <1

Consistency Firm Medium Soft -

Position Posterior Midline Anterior -

Head Station - 3 - 2 - 1, 0 +1, +2

• Total Score – 13

• Unfavorable Score – 0-5

• Favorable Score - 6-13

• Bishop score >8 is a good index of inducibility

Methods of cervical ripeningPharmacological methods

• Oxytocin

• Prostaglandins

-E2(dinoprostone,prepidil,cervidil)

-E1(misoprost)

• Steroid receptor antagonists

-Mifepristone (RU486)

-Onapristone

• Relaxin

Mechanical methods

• Membrane stripping

• Amniotomy

• Mechanical dilators

• Transcervical balloon cathetersWith extraamniotic saline infusionWith concomitant oxytocin administration

Methods of Induction of labor

• Medical – Prostaglandins (PGE2, PGE1)

- Oxytocin

- Mifepristone

• Surgical - Artificial rupture of membranes

- Stripping the membranes

• Combined - Medical + Surgical

Prostaglandin E2

• Gel preparation with 0.5mg in 2.5ml in a prefilled syringe for intracervical administration (prepidil/ dinoprostone

• With the woman in dorsal the tip of a prefilled syringe is placed intracervically and the gel is deposited just below the internal cervical os.The woman should remain reclined for at least 30 minutes.

• Dose repeated every 6 hours with a maximum of 3 doses

• Subsequent augmentation with oxytocin if needed to be started after 6 hours

• Side effects- uterine tachysystole• Contraindication- asthma, glaucoma , liver disease

Prostaglandin E1• Used as 25µg per vaginally every 4 hours or 50µg

per orally every 3-6 hours• Sublingual and buccal routes associated with rapid

onset action and more bioavalibility• Maximum dose of 200µg given• Synto augmentation if required to be started after 6

hours• Side effects- uterine tachysystole, fetal distress,

uterine rupture• Contraindicated in patients with previous uterine

scar, liver disease and renal disease

Oxytocin • Polypeptide hormone produced in hypothalamus,

secreted from posterior pituitary• Synthetic analogue of used as uterotonic and for

induction• Myometrial sensitivity increases with gestational age,

with rapid increase during labour• Effective means of induction in women with ripe cervix • Because of short half life (3-4min) used as iv infusion.

Plasma levels falls rapidly when iv infusion stopped.• Oxytocin infusion is commenced at the rate of

1-2miu/min and gradually dose increment at 15-30min

2.5 IU Oxytocin in 500ml RL(concentration- 5mIU/ml)

8 drops- 2.5mIU/ml

16 drops- 5mIU/ml

24 drops- 7.5mIU/ml

32 drops- 10 mIU/ml

40 drops- 12.5mIU/ml

48 drops- 15 mIU/ml

56 drops- 17.5 mIU/ml

60 drops- 20 mIU/ml

Complications

• Uterine overactivity

• Water intoxication

• Hypotension

• Uterine rupture

• Neonatal jaundice

Mifepristone

• Progestrone receptor antagonist

• Blocks both progestrone and glucocorticoid receptors

• 200mg vaginally daily for 2days has been found to ripen the cervix and to induce labour

Membrane stripping• Digital separation of chorioamniotic

membrane from wall of cervix and lower uterine segment

• Results in local release of endogenous prostaglandins

• Vertex should be well applied to cervix and os should be dilated to allow examining finger

• Complications- membrane rupture, haemorrhage from disruption of occult placenta praevia, chorioamnionitis

Transcervical Foley’s catheter• placed through cervical os inflated with 30-50cc saline

• Downward tension that is created by taping the catheter to the thigh can lead to cervical ripening

• The catheter is left in place until it spontaneously falls out or upto 24 hours

• Intracervical foley’s catheter can be combined with oxytocin or vaginal misoprostol or they can be started 12-24 hours after insertion.

• Preferred in woman where prostaglandins are contraindicated.

• Cotraindication-low lying placenta,APH, rupture of membrane, cervicitis

Factors that increase success of labour induction

• Favourable cervix

• Multiparity

• Bodymass index<30

• Birthweight<3500gm