10.4 Multiple Gestation, Fetal Growth Disorders, Amniotic Fluid Abnormalities, Malpresentation & Postterm Pregnancy
Key Takeaways
Monochorionic twins need ultrasound every 2 weeks from 16 weeks to detect twin-twin transfusion syndrome; ACOG delivery timing is 38 0/7–38 6/7 weeks for dichorionic and 34 0/7–37 6/7 weeks for monochorionic-diamniotic twins.
SMFM defines fetal growth restriction as an estimated fetal weight or abdominal circumference below the 10th percentile; umbilical artery Doppler findings guide surveillance and delivery timing.
ACOG suggests offering cesarean birth for suspected macrosomia when the estimated fetal weight is at least 5,000 g without diabetes or at least 4,500 g with diabetes.
External cephalic version is offered at 37 0/7 weeks or later for breech presentation when there are no contraindications, and Rh(D)-negative patients receive anti-D immune globulin.
Late-term pregnancy begins at 41 0/7 weeks and postterm at 42 0/7 weeks; antenatal testing starts at 41 weeks, induction can be considered from 41 0/7 weeks, and ACOG recommends induction after 42 0/7 and by 42 6/7 weeks.
Multiple Gestation
Twins occur in about 3% of U.S. births, more often with assisted reproduction and older maternal age.
- Maternal risks: Preeclampsia (aspirin is indicated), gestational diabetes, anemia, hyperemesis, preterm birth (about 60% of twins deliver before 37 weeks), and postpartum hemorrhage.
- Fetal risks: Preterm birth, growth restriction, growth discordance (20% or more), anomalies, and stillbirth; monochorionic twins add twin-twin transfusion syndrome (TTTS), which occurs in about 10%–15% of monochorionic-diamniotic pairs, and monoamniotic twins add cord entanglement.
- Care: Determine chorionicity in the first trimester. Ultrasound every 4 weeks or so for dichorionic twins; every 2 weeks from 16 weeks for monochorionic twins to watch for TTTS (polyhydramnios in the recipient and oligohydramnios in the donor). Weight gain goal for a normal-BMI twin pregnancy is about 37–54 lb.
| Twin Type | ACOG Delivery Timing (uncomplicated) |
|---|---|
| Dichorionic-diamniotic | 38 0/7–38 6/7 weeks |
| Monochorionic-diamniotic | 34 0/7–37 6/7 weeks |
| Monochorionic-monoamniotic | 32 0/7–34 0/7 weeks (usually by cesarean) |
Vaginal birth is reasonable when the first twin is cephalic; cesarean is usual when the first twin is not cephalic.
Fetal Growth Restriction (FGR)
- Definition (SMFM 2020): Estimated fetal weight (EFW) or abdominal circumference below the 10th percentile; severe FGR is below the 3rd percentile. Small for gestational age (SGA) describes a newborn whose birth weight is below the 10th percentile.
- Causes: Maternal (hypertension, preeclampsia, diabetes with vascular disease, smoking, substance use, malnutrition, autoimmune disease), placental (abnormal spiral artery remodeling, abruption, cord abnormalities), and fetal (aneuploidy, structural anomalies, infection such as CMV).
- Evaluation: Detailed anatomy survey; genetic counseling and diagnostic testing for early-onset FGR (before 32 weeks) or FGR with anomalies or polyhydramnios; CMV testing.
- Surveillance: Umbilical artery Doppler is the key test; add amniotic fluid assessment and NST or biophysical profile.
| Doppler Finding | Typical Delivery Timing (SMFM) |
|---|---|
| EFW 3rd–10th percentile, normal Doppler | 38 0/7–39 0/7 weeks |
| EFW below the 3rd percentile or decreased diastolic flow | 37 0/7 weeks |
| Absent end-diastolic velocity | 33 0/7–34 0/7 weeks |
| Reversed end-diastolic velocity | 30 0/7–32 0/7 weeks |
Give antenatal corticosteroids when delivery before 34 weeks is likely, and magnesium for neuroprotection before 32 weeks.
Macrosomia and Large for Gestational Age
- Definitions: Birth weight of 4,000 g or 4,500 g or more (macrosomia); large for gestational age is above the 90th percentile.
- Risk factors: Diabetes (pregestational or gestational), obesity, excessive weight gain, prior macrosomic infant, and postterm pregnancy.
- Limitations: Ultrasound and clinical estimates of fetal weight are imprecise.
- ACOG Practice Bulletin 216: Suspected macrosomia alone is not an indication for induction before 39 weeks. Offer scheduled cesarean when EFW is at least 5,000 g without diabetes or at least 4,500 g with diabetes to reduce shoulder dystocia and brachial plexus injury.
Amniotic Fluid Abnormalities
| Finding | Definition | Common Causes | Management |
|---|---|---|---|
| Oligohydramnios | Deepest vertical pocket <2 cm (preferred) or AFI ≤5 cm | PPROM, placental insufficiency (FGR), renal agenesis or obstruction, postterm pregnancy, NSAIDs or ACE inhibitors | Rule out rupture of membranes and FGR; hydrate; increased surveillance; isolated oligohydramnios at term is delivered at 36 0/7–37 6/7 weeks |
| Polyhydramnios | Deepest vertical pocket ≥8 cm or AFI ≥24 cm | Maternal diabetes, fetal swallowing defects (esophageal or duodenal atresia, neuromuscular disorders), fetal anemia or hydrops, twins with TTTS, idiopathic | Diabetes screening, detailed anatomy scan, antibody screen, infection testing; risks include preterm labor, malpresentation, cord prolapse at rupture, and postpartum hemorrhage |
Malpresentation
- Breech presentation affects about 3%–4% of term pregnancies (frank, complete, or footling).
- External cephalic version (ECV): Offer at 37 0/7 weeks or later (when spontaneous version is unlikely but an emergency term delivery is acceptable). Success is about 50%–60%, higher in multiparous patients. Contraindications include placenta previa, a nonreassuring fetal tracing, and any contraindication to vaginal birth. Use fetal monitoring before and after, consider tocolysis with terbutaline, and give anti-D immune globulin to Rh(D)-negative patients.
- Delivery: Planned cesarean is common for persistent breech; planned vaginal breech birth is reasonable in selected cases under hospital protocols with experienced clinicians (ACOG Committee Opinion 745).
- Transverse lie at term needs ECV or cesarean, and rupture of membranes with a transverse lie raises the risk of cord prolapse. Face, brow, and compound presentations are identified in labor; a mentum posterior face presentation cannot deliver vaginally.
Late-Term and Postterm Pregnancy
- Definitions: Late term is 41 0/7–41 6/7 weeks; postterm is 42 0/7 weeks or later. Accurate first-trimester dating sharply reduces false postterm diagnoses.
- Risks: Stillbirth, macrosomia and shoulder dystocia, oligohydramnios, meconium aspiration, and placental insufficiency (postmaturity syndrome).
- Management (ACOG Practice Bulletin 146): Begin antenatal surveillance (for example, NST plus amniotic fluid assessment) at 41 0/7 weeks. Induction can be considered from 41 0/7 to 42 0/7 weeks and is recommended after 42 0/7 and by 42 6/7 weeks. Trials such as SWEPIS and INDEX found better perinatal outcomes with induction at 41 weeks, so many clinicians now induce at 41 weeks. Elective induction at 39 weeks in low-risk nulliparous patients is a reasonable option: the ARRIVE trial found it did not increase, and modestly lowered, cesarean rates.
A 32-year-old has a monochorionic-diamniotic twin pregnancy. At 20 weeks, ultrasound shows a deepest vertical pocket of 9 cm around twin A with a distended bladder, and 1.5 cm around twin B, whose bladder is barely visible. What is the most likely diagnosis?
Twin-twin transfusion syndrome
Normal discordance between dichorionic twins
Bilateral renal agenesis in twin A
Maternal gestational diabetes causing polyhydramnios in both sacs
At 34 weeks, a fetus has an estimated fetal weight at the 2nd percentile, and umbilical artery Doppler shows absent end-diastolic velocity. Amniotic fluid is normal, and the NST is reactive. According to SMFM guidance, what is the most appropriate plan?
Continue weekly umbilical artery Doppler surveillance and plan delivery at 39 weeks.
Repeat the growth ultrasound in 4 weeks before deciding on the timing of delivery.
Start high-dose aspirin and bed rest to improve placental blood flow and fetal growth.
Plan delivery at 33 0/7–34 0/7 weeks, with antenatal corticosteroids if not already given.
A 29-year-old G2P1, Rh(D) negative and unsensitized, has a confirmed frank breech presentation at 37 weeks. The placenta is fundal, the fetal tracing is reactive, and she has no contraindication to vaginal birth. What is the most appropriate recommendation?
Schedule a cesarean delivery at 37 weeks without discussing version or other options.
Offer external cephalic version with fetal monitoring and give anti-D immune globulin.
Wait for spontaneous version and schedule induction only at 42 weeks.
Induce labor today for a planned vaginal breech birth without further counseling.
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