Obstetrics and Gynaecology chapters
Preterm labour and prelabour rupture of membranes
Labour before 37 weeks and rupture of the membranes before labour: causes and risk factors, how to predict preterm birth, tocolytics, steroids, magnesium for neuroprotection, erythromycin in PPROM, and prevention with progesterone and cerclage.
- Preterm labour is labour before 37 weeks; PPROM is rupture of membranes before labour and before 37 weeks. Preterm birth is the leading cause of perinatal death and of death under 5 years worldwide.
- Key causes: infection (chorioamnionitis), multiple pregnancy, cervical weakness, bleeding, uterine anomalies; the strongest predictor is a previous preterm birth. Fetal fibronectin and transvaginal cervical length help predict delivery.
- Steroids give the biggest benefit; tocolysis (nifedipine or atosiban) only buys time for steroids and transfer; magnesium protects the brain; in PPROM give erythromycin, watch for chorioamnionitis and never give tocolytics.
On this page
Overview
Labour that starts before 37 completed weeks of pregnancy is called preterm labour (PTL). Preterm prelabour rupture of membranes (PPROM) is rupture of the membranes before 37 weeks and before labour starts. Preterm birth is the most important cause of perinatal death and disability worldwide and the leading cause of death in children under 5. About 15 million babies are born preterm each year, mostly in lower-income countries such as Pakistan, where survival at a given gestation is much worse. In high-income settings a baby born at 24 weeks has about a 50% chance of survival; in low-income settings similar survival is reached only at about 34 weeks.
Types of preterm birth
| Type | Share |
|---|---|
| Spontaneous preterm labour | About 50% |
| PPROM | About 25% |
| Medically indicated (pre-eclampsia, FGR, maternal disease) | About 25% |
Causes and risk factors
| Group | Factors |
|---|---|
| Previous history | Previous preterm birth (about 4 times the risk) or mid-trimester loss |
| Infection | Chorioamnionitis (especially before 32 weeks), bacterial vaginosis, urinary infection |
| Overdistension | Multiple pregnancy (about half of twins deliver preterm), polyhydramnios |
| Cervix | Cervical weakness (painless mid-trimester dilatation), previous cone biopsy or repeated dilatation |
| Uterus | Müllerian anomalies (bicornuate, septate), fibroids |
| Bleeding | APH, abruption, subchorionic haematoma (thrombin stimulates contractions) |
| Maternal | Teenage or older mother, low socioeconomic status, poor nutrition, smoking, cocaine, stress, abdominal surgery in pregnancy |
| Fetal | Fetal anomaly, FGR (fetal stress) |
Smoking is the main modifiable risk factor; stopping smoking reduces preterm birth.
Why infection matters
Ascending infection from the vagina inflames the membranes. Cytokines (IL-1, IL-6, TNF) and prostaglandins trigger contractions and membrane rupture, and the same inflammation injures the fetal brain (periventricular leukomalacia, cerebral palsy).
Diagnosis of preterm labour
- Regular painful contractions with cervical change (effacement and dilatation).
- Many women with "threatened" preterm labour are not in labour: up to 70% do not deliver during that admission.
Prediction tests
| Test | Use |
|---|---|
| Fetal fibronectin (fFN) | Glycoprotein "glue" between chorion and decidua; in cervicovaginal fluid at 22-36 weeks it predicts delivery. A negative test has a very high negative predictive value, so most women can go home |
| Transvaginal cervical length | More accurate than abdominal scan or finger; a short cervix means higher risk. Used for serial screening of high-risk women from about 16 weeks |
| History | Previous preterm birth or mid-trimester loss |
Management of preterm labour
Aims: gain time for steroids and transfer to a unit with neonatal intensive care, and protect the baby's lungs and brain.
1. Antenatal corticosteroids
- Betamethasone or dexamethasone IM to the mother (both cross the placenta).
- They have the greatest effect on preterm outcome: a single course cuts neonatal death by about 31%, respiratory distress syndrome by 44% and intraventricular haemorrhage by 46%.
- They also aid maturation of other organs.
- Usually given before 34 weeks (later in some guidelines, e.g. before elective caesarean). In diabetic mothers, steroids raise glucose and need extra insulin.
2. Tocolysis
Tocolytics delay delivery (typically by 48 hours) but do not improve neonatal outcome by themselves.
| Drug | Mechanism | Key points |
|---|---|---|
| Nifedipine | Calcium channel blocker (L-type) | First choice in many guidelines; headache, flushing, hypotension |
| Atosiban | Oxytocin receptor antagonist | First choice alternative; fewest side-effects |
| Indomethacin | COX inhibitor, blocks prostaglandins | Effective, but can cause premature closure of the ductus arteriosus (risk rises sharply after 32 weeks), oligohydramnios, neonatal kidney problems and NEC |
| Beta-agonists (ritodrine, salbutamol, terbutaline) | Beta-2 stimulation raises cAMP | Rarely used now; pulmonary oedema, tachycardia; dangerous in twins and heart disease |
| Magnesium sulphate | Calcium antagonism | Poor tocolytic; used instead for fetal neuroprotection |
Contraindications to tocolysis: chorioamnionitis or PPROM, abruption or significant bleeding, fetal death or lethal anomaly, fetal distress, severe pre-eclampsia, advanced labour.
Magnesium sulphate in preterm labour is given to reduce cerebral palsy in the baby, not to stop contractions.
Indomethacin (and other NSAIDs) late in pregnancy can close the ductus arteriosus in utero, since prostaglandins keep it open.
3. Other steps
- Magnesium sulphate for neuroprotection when birth is imminent at early gestations.
- Intrapartum antibiotics against group B streptococcus: prematurity under 37 weeks is a recognised indication (penicillin, or clindamycin if allergic).
- Continuous fetal monitoring as appropriate; neonatal team present.
- In utero transfer to a unit with NICU is safer than transferring the baby after birth.
Preterm prelabour rupture of membranes (PPROM)
Facts
- Affects about 2% of pregnancies; causes about one third of preterm births.
- Half deliver within 1 week and three quarters within 2 weeks; the earlier the rupture, the shorter this gap.
- Infection complicates about a third of pregnancies after PPROM.
- PPROM before about 23 weeks risks pulmonary hypoplasia (about 50% at 19 weeks, 10% at 25 weeks).
Diagnosis
- History of a gush or continuous leak of fluid.
- Sterile speculum examination showing a pool of liquor in the posterior fornix.
- Ultrasound may show reduced liquor.
- Avoid digital vaginal examination: it introduces infection and shortens the time to delivery.
Watching for chorioamnionitis
- Maternal fever, tachycardia, uterine tenderness, offensive discharge.
- Fetal tachycardia on CTG.
- Rising white cell count and C-reactive protein.
- Swabs are taken but correlate poorly with infection.
Management
| Situation | Plan |
|---|---|
| Under 34 weeks, no infection | Conservative: admit, erythromycin for 10 days, steroids, monitor for infection; no tocolysis |
| Signs of chorioamnionitis (any gestation) | IV antibiotics and deliver, whatever the gestation |
| 34-37 weeks | Balance prematurity against infection risk; local protocols differ, and many units now lean to delivery around 34-37 weeks |
| 37 weeks or more (term PROM) | Induce labour (or follow local expectant plan for a short time); GBS prophylaxis if membranes ruptured more than 18 hours |
The ORACLE studies showed that erythromycin improves outcome after PPROM, but antibiotics give no benefit when membranes are intact in preterm labour.
Tocolysis is contraindicated in PPROM because it may delay delivery of an infected baby.
Prevention of preterm birth
Progesterone
Helps keep the uterus quiet. Vaginal progesterone may lower the risk when the cervix is short; IM hydroxyprogesterone caproate has been used after a previous preterm birth. Evidence is mixed.
Cervical cerclage
| Indication | When |
|---|---|
| History-indicated | Several previous mid-trimester losses or preterm births; usually placed after 12-14 weeks |
| Ultrasound-indicated | Cervix shortens to under about 25 mm in a woman with previous preterm birth or cervical surgery |
| Rescue | Cervix already dilating without contractions |
| Type | Technique |
|---|---|
| McDonald | Vaginal purse-string suture at the cervicovaginal junction, no bladder mobilisation |
| Shirodkar | Higher vaginal suture after pushing the bladder up |
| Transabdominal | At the cervicoisthmic junction by laparotomy or laparoscopy; after failed vaginal cerclage; needs caesarean delivery |
- A non-absorbable tape (e.g. Mersilene) is used; a vaginal suture can usually be removed without anaesthesia before labour.
- Cerclage does not help multiple pregnancy.
"McDonald stays Down low, Shirodkar Sits higher."
Other measures
Stop smoking; screen high-risk women for bacterial vaginosis and treat; treat asymptomatic bacteriuria.
Expect: the 37-week definition; previous preterm birth as the strongest predictor and smoking as the modifiable factor; infection and multiple pregnancy as causes; fetal fibronectin and its negative predictive value; transvaginal cervical length; steroids as the most useful intervention and their effect on RDS and IVH; nifedipine or atosiban as tocolytics; indomethacin closing the ductus; pulmonary oedema with beta-agonists; magnesium for neuroprotection; PPROM diagnosis by speculum, avoiding digital examination, erythromycin, no tocolysis and delivery for chorioamnionitis; McDonald versus Shirodkar cerclage.
Quick revision
- Preterm labour: before 37 weeks; PPROM: membranes rupture before labour and before 37 weeks.
- Previous preterm birth: about 4 times the risk; smoking is modifiable.
- fFN negative: safe to send most women home.
- Steroids: biggest benefit (less death, RDS, IVH).
- Tocolysis: nifedipine or atosiban, only to buy time; never in PPROM or infection.
- Indomethacin: ductus closure, oligohydramnios, NEC.
- PPROM: speculum, no digital exam, erythromycin 10 days, deliver if chorioamnionitis.
- Cerclage: history, ultrasound (cervix under 25 mm) or rescue; McDonald or Shirodkar.
Written by The House Job from standard references (Obstetrics by Ten Teachers).
FAQ
Do tocolytics improve the baby's outcome?
Not on their own; their value is in delaying birth long enough to give steroids and move the mother to a unit with neonatal intensive care.
Why are antibiotics given in PPROM but not in preterm labour with intact membranes?
Large studies showed that erythromycin improves outcomes after membrane rupture, while antibiotics in women with intact membranes gave no benefit.
Why is a digital examination avoided in PPROM?
It can carry vaginal bacteria up through the cervix, raising the risk of chorioamnionitis and shortening the time to delivery.
What is cervical weakness?
A cervix that opens painlessly in the second trimester without contractions, often after cervical surgery, and which may be supported by a cerclage.