173 PROM, Breech and Twins for the PANCE

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The water breaks at 30 weeks. The baby’s head is in the fundus at 37. The ultrasound shows one placenta and two babies. None of these is an emergency yet, but each one changes the delivery plan, and one number decides it every time: 34 weeks for ruptured membranes, 37 weeks for breech, and how many placentas for twins.

Premature Rupture of Membranes (PROM)

• Rupture of the membranes before labor starts.
  • Premature means before labor, not before term. Water breaks at 40 weeks with no contractions = PROM.
  • PROM: 37 weeks or later.
  • Preterm PROM (PPROM): before 37 weeks.

Risk Factors

• Prior PPROM, the strongest predictor.
• Infection:
  • Bacterial vaginosis.
  • Sexually transmitted infections.
  • Group B strep (GBS).
• Overdistended uterus:
  • Multiple gestation.
  • Polyhydramnios.
• Short cervix.
• Smoking.
• Bleeding earlier in pregnancy.

Clinical Presentation

• Sudden gush or steady leak of clear fluid, usually without contractions.
• Look-alikes:
  • Urine leakage.
  • Heavy discharge.
  • Loss of the mucus plug.
• The question stem would likely describe a woman at 30 weeks with a sudden gush of clear fluid and no contractions.

Diagnostics

• Sterile speculum exam:
  • Pooling: fluid in the posterior fornix, or leaking from the cervix with a cough.
  • Nitrazine paper turns blue: amniotic fluid is alkaline (pH 7.0 to 7.5), the vagina is acidic (pH 3.8 to 4.5).
    • False positives:
      • Blood.
      • Semen.
      • Bacterial vaginosis.
  • Ferning: dried amniotic fluid crystallizes into a fern pattern under the microscope. More specific than nitrazine.
• Ultrasound: oligohydramnios supports the diagnosis. Normal fluid doesn’t rule it out.
• No digital cervical exam unless she’s in labor.
  • Pushes vaginal bacteria up through the cervix.
  • Makes labor start sooner.

Treatment

• 34 weeks or later
  • Deliver: induce with oxytocin.
    • The fetal lungs are mature enough.
    • Infection risk climbs every hour the membranes are open.
• Under 34 weeks, no infection
  • Admit and buy time.
  • Prematurity is the bigger danger.
  • Corticosteroids: betamethasone 12 mg IM, 2 doses 24 hours apart, to mature the fetal lungs.
  • Begin antibiotics:
    • IV ampicillin + erythromycin for 48 hours.
    • Then oral amoxicillin + erythromycin for 5 days.
    • Azithromycin can replace erythromycin as the macrolide.
    • Delays labor and lowers infection.
    • Avoid amoxicillin-clavulanate → necrotizing enterocolitis.
  • Magnesium sulfate under 32 weeks if delivery is likely:
    • Fetal neuroprotection, less cerebral palsy.
    • Not a tocolytic.
• GBS prophylaxis (IV penicillin):
  • GBS positive.
  • GBS unknown plus any of:
    • Preterm.
    • Rupture 18 hours or more.
    • Fever.
• Deliver at any gestational age for:
  • Chorioamnionitis.
  • Abruption.
  • Nonreassuring fetal heart tracing.
  • Active labor.
• Under 23 weeks: too early to survive. Counsel the family.
  • Pulmonary hypoplasia: the lungs can’t develop without amniotic fluid.

Chorioamnionitis

• Infection of the amniotic fluid, membranes, and placenta (intra-amniotic infection).
• Maternal fever 39.0°C or higher alone makes the diagnosis.
• 38.0 to 38.9°C plus one of:
  • Fetal tachycardia, heart rate over 160.
  • Maternal WBC over 15,000.
  • Purulent or foul-smelling fluid from the cervix.
• Uterine tenderness on exam.
• IV ampicillin + gentamicin, and deliver.
  • Antibiotics alone don’t clear it.
  • Not by itself a reason for cesarean.

Exam Keys

• PROM = before labor. PPROM = before 37 weeks.
• Sterile speculum, never a finger: pooling, nitrazine blue, ferning.
• 34 weeks or later → deliver. Under 34 → steroids, antibiotics, wait.
• Magnesium under 32 weeks = fetal brain protection, not a tocolytic.
• Fever + fetal tachycardia after rupture = chorioamnionitis. Ampicillin + gentamicin, then deliver.

Breech Presentation

• The buttocks or feet present first instead of the head.
• Common early, rare at term:
  • About 1 in 4 at 28 weeks.
  • 3 to 4% at term.
• Types:
  • Frank: hips flexed, knees straight, feet up by the face. The most common.
  • Complete: hips and knees both flexed, sitting cross-legged.
  • Footling (incomplete): one or both feet first. Highest cord prolapse risk.

Risk Factors

• Prematurity, the most common.
• Too much room:
  • Polyhydramnios.
  • Grand multiparity.
• Too little room:
  • Oligohydramnios.
  • Multiple gestation.
• Something in the way:
  • Placenta previa.
  • Fibroids.
  • Uterine anomaly (bicornuate uterus).
• Fetal anomalies:
  • Hydrocephalus.
  • Anencephaly.
  • Neuromuscular disease.
• Prior breech.

Clinical Presentation

• Leopold maneuvers: four hand positions on the abdomen that map how the fetus is lying.
  • Hard, round, movable head in the fundus.
  • Soft, irregular buttocks low.
• Fetal heart tones loudest above the umbilicus.
• The question stem would likely describe a hard, round, movable mass in the fundus at 37 weeks.

Diagnostics

• Ultrasound confirms it, and shows:
  • Type of breech.
  • Amniotic fluid.
  • Fetal anomalies.
  • Placental location.

Treatment

• Under 37 weeks: wait. Most turn on their own.
• 37 weeks: external cephalic version (ECV), hands on the abdomen rotate the baby head-down.
  • Succeeds about half the time.
  • Terbutaline relaxes the uterus and improves success.
  • Rh-negative → RhoGAM. ECV can mix fetal and maternal blood.
• No ECV with:
  • Placenta previa.
  • Prior classical incision.
  • Nonreassuring tracing.
  • Recent bleeding or abruption.
  • Multiple gestation.
  • Major uterine anomaly.
• ECV fails or declined → planned cesarean at 39 weeks.
• After birth: breech → risk of developmental dysplasia of the hip (DDH).
  • Hip ultrasound at about 6 weeks, even with a normal hip exam.

Exam Keys

• Hard, round head in the fundus + heart tones above the umbilicus = breech.
• Frank = most common. Footling = highest cord prolapse risk.
• 37 weeks → ECV. Fails → cesarean at 39.
• Never ECV with a previa. Rh-negative gets RhoGAM after a version.
• Breech baby → hip ultrasound at 6 weeks for DDH.

Multiple Gestation

• Two or more fetuses.
• Chorionicity (how many placentas) drives the risk. The chorion is the outer membrane that forms the placenta.
  • Dichorionic: each twin has its own placenta and blood supply.
  • Monochorionic: one shared placenta with shared blood vessels. Higher risk.

Types

• Dizygotic (fraternal): two eggs, two sperm. About 2/3 of twins.
  • Always dichorionic diamniotic (di-di): two placentas, two sacs.
• Monozygotic (identical): one fertilized egg splits. About 1/3 of twins. The later the split, the more they share:
  • Days 0 to 3 → di-di.
  • Days 4 to 8 → monochorionic diamniotic (mono-di): one placenta, two sacs. The most common identical type.
  • Days 8 to 12 → monochorionic monoamniotic (mono-mono): one placenta, one sac.
  • Day 13 or later → conjoined twins.

Risk Factors

• These raise dizygotic twinning (more than one egg released):
  • Assisted reproduction:
    • Ovulation induction (clomiphene, gonadotropins).
    • In vitro fertilization (IVF).
  • Advanced maternal age.
  • Maternal family history.
  • Black race.
  • Higher parity.

Clinical Presentation

• Uterus larger than dates.
• hCG and alpha-fetoprotein (AFP) higher than expected.
• More hyperemesis.
• Higher rates of every pregnancy complication:
  • Preterm birth, the most common. Average delivery around 35 weeks.
  • Preeclampsia.
    • Twins alone qualify for low-dose aspirin (81 mg) from 12 weeks.
  • Gestational diabetes.
  • Anemia.
  • Postpartum hemorrhage from uterine atony.
  • Growth restriction.
  • Discordant growth: one twin 20% or more smaller.
• The question stem would likely describe a fundal height well ahead of dates, or an unexpectedly high AFP.

Diagnostics

• Ultrasound confirms it and sets chorionicity in the first trimester (before 14 weeks).
  • Lambda (twin peak) sign: triangle of placenta wedging into the dividing membrane → dichorionic.
  • T sign: thin membrane meeting the placenta at a right angle → monochorionic diamniotic.
  • No dividing membrane → monoamniotic.
  • Different sexes → dizygotic → dichorionic.
• Monochorionic twins: ultrasound every 2 weeks for twin-twin transfusion.

Monochorionic Complications

• Twin-twin transfusion syndrome (TTTS): vessels in the shared placenta connect the circulations, and blood flows one way. About 10 to 15% of mono-di twins.
  • Donor twin: less blood → less urine → oligohydramnios.
    • The “stuck twin,” pinned against the uterine wall.
    • Growth restricted.
    • Anemic.
  • Recipient twin: more blood → more urine → polyhydramnios.
    • Polycythemia.
    • Volume overload.
    • Heart failure.
    • Hydrops.
  • Amniotic fluid is mostly fetal urine, so the fluid tells you which twin is which.
  • Treatment: fetoscopic laser ablation of the connecting vessels.
• Mono-mono: no dividing membrane → cord entanglement. Highest fetal loss of any twin type.

Treatment

• Delivery timing, uncomplicated twins. The more they share, the earlier:
  • Di-di: 38 weeks.
  • Mono-di: 34 to 37 weeks.
  • Mono-mono: 32 to 33 weeks, by cesarean.
• Delivery route depends on twin A, the twin closest to the cervix:
  • Twin A vertex → vaginal delivery is reasonable.
  • Twin A breech or transverse → cesarean.
  • Triplets or more → cesarean.
  • After twin A delivers, watch for abruption and twin B cord prolapse.

Exam Keys

• The later the split, the more they share: di-di, mono-di, mono-mono, conjoined.
• Lambda sign = two placentas. T sign = one.
• Donor twin = oligohydramnios, the stuck twin. Recipient = polyhydramnios, heart failure.
• Di-di at 38. Mono-di at 34 to 37. Mono-mono at 32 to 33, by cesarean.
• Twin A vertex → vaginal trial. Twin A not vertex → cesarean.

Putting It Together

• PPROM: 34 weeks. Breech: 37 weeks. Twins: how many placentas, then twin A picks the route.
• All three set up cord prolapse: ruptured membranes, a footling breech, the second twin.
• Trap: the right move at the wrong time. ECV at 34 weeks. Delivering PPROM at 30 weeks with no infection. Mono-di twins carried to 39.

Study Tip: Decide What to Study

You can’t study everything, and trying to is a fool’s game. Some things are more important to learn than other things. If you could only hold on to one thing from this episode, make it the 34-week line for ruptured membranes: what you do before 34 weeks and what you do after. The next one is twin-twin transfusion. Stop trying to cover it all and start deciding what you’re going to study.

The new edition of The Final Step

I’m working hard to get the new edition of The Final Step out by the end of October: 2,000 questions, only the most important stuff, to lock it into your brain for exam day. The first run is 50 copies. Get on the list to hear as soon as it’s ready.

Get 26 Ob-Gyn questions straight from The Final Step.

Give me those OB-GYN questions!