Clinical overview
Multiple pregnancy — twins, triplets and higher orders — is one of the highest-risk states in routine obstetrics, and the registrar must be able to manage it confidently because the rising tide of assisted reproduction and advancing maternal age has pushed twin rates above their historical baseline. The natural dizygotic twinning rate is influenced by race, with sub-Saharan African populations carrying among the highest spontaneous rates in the world, so in South African practice twins are not a rarity but a regular feature of the antenatal clinic and the labour ward. Every adverse outcome in obstetrics is amplified in the multiple: preterm birth, pre-eclampsia, gestational diabetes, growth restriction, antepartum and postpartum haemorrhage, malpresentation and operative delivery are all more common. Perinatal mortality is several-fold higher than in singletons, and most of that excess is driven by prematurity and by the chorionicity-specific complications of monochorionic placentation.
The single most important determination after diagnosing a twin pregnancy is chorionicity — not zygosity. Chorionicity dictates the entire surveillance schedule, the risk of unique complications such as twin-to-twin transfusion syndrome (TTTS), and the timing and mode of delivery. The objective here is the uncomplicated multiple pregnancy and its diagnosis and delivery, including vaginal birth; but "uncomplicated" can only be claimed after chorionicity is fixed and the chorionicity-driven complications have been actively screened for and excluded. This chapter sits beside high-risk-pregnancy-risks and the obstetric-emergency chapters, and the registrar should read it with antenatal-booking, gestational-age-assessment and complicated-labour alongside.
Core knowledge
Zygosity and chorionicity
- Dizygotic (DZ) twins arise from two separately fertilised ova: always two placentas, two chorions, two amnions — dichorionic diamniotic (DCDA). They are no more genetically alike than any siblings and may be different sexes.
- Monozygotic (MZ) twins arise from a single zygote that divides. The resulting chorionicity depends on when the split occurs:
- Split at days 0–3 (morula/pre-blastocyst): DCDA (about a third of MZ).
- Split at days 4–8 (blastocyst): monochorionic diamniotic (MCDA) — the commonest MZ form.
- Split at days 8–13 (after amnion forms): monochorionic monoamniotic (MCMA).
- Split after day 13: incomplete — conjoined twins.
All monochorionic twins are monozygotic; the placental vascular anastomoses they share are the source of TTTS, twin anaemia–polycythaemia sequence (TAPS), selective fetal growth restriction with abnormal Doppler, and the catastrophic risk to the survivor after a single intrauterine death. Dichorionic twins do not share circulation and so escape these specific syndromes, though they remain at raised risk of prematurity, growth restriction and pre-eclampsia.
Figure J23.1 — Chorionicity pathway for twins, showing dizygotic DCDA pregnancy, monozygotic split timing, lambda/T-sign ultrasound clues, and monochorionic risk syndromes.
Why multiples are high risk
The shared maternal physiology is stretched: plasma volume expansion and cardiac output are greater, anaemia is more common, and uterine over-distension predisposes to preterm labour and to uterine atony with postpartum haemorrhage. Spontaneous preterm birth before 37 weeks affects roughly six in ten twin pregnancies, and the median gestation at birth falls as the fetal number rises. Pre-eclampsia, gestational diabetes and obstetric cholestasis are all over-represented. Growth restriction may be of both fetuses or, classically in monochorionic pairs, selective. These are the reasons a twin pregnancy is booked and followed in a higher level of care.
Assessment
Diagnosis
Multiple pregnancy is diagnosed by ultrasound, ideally at the first-trimester scan. Clinical suspicion (uterus large for dates, two fetal poles, more than two fetal heart tones, hyperemesis) should always be confirmed sonographically. The NICE multiple-pregnancy guidance (NG137) and the SA National Integrated Maternal and Perinatal Care Guideline (NDoH, 2024) both make early dating-and-chorionicity ultrasound the cornerstone of care.
Determining chorionicity is most reliable between 11+0 and 13+6 weeks and should be documented in the notes and on the report:
- Two separate placental masses → dichorionic.
- The membrane–placenta junction:
- Lambda (λ) / "twin peak" sign — a triangular wedge of placental tissue extending into the inter-twin membrane base → dichorionic.
- T sign — the inter-twin membrane meets the placenta at a right angle with no wedge → monochorionic.
- Inter-twin membrane thickness — thin (two layers) suggests monochorionic; thick (three or four layers) suggests dichorionic — a softer, later sign.
- Discordant fetal sex proves dichorionicity.
If chorionicity cannot be assigned with confidence — for example a late-booking woman — manage as monochorionic (the higher-risk assumption) until proven otherwise, and refer for an expert scan. Each fetus should be labelled and mapped (site, cord insertion, relation to cervix) at this scan and the labelling kept consistent at every subsequent scan, so that a growth- or Doppler-discordant fetus is tracked as the same fetus throughout.
Establishing gestational age
Date the pregnancy from the larger crown–rump length in the first trimester (or, if presenting later, the larger head circumference), to avoid mistakenly dating off an already-compromised smaller twin. See gestational-age-assessment.
Ongoing antenatal surveillance
Surveillance is chorionicity-specific and more intensive than for singletons:
- Dichorionic twins: serial growth scans approximately every 4 weeks from around 20 weeks, with umbilical-artery Doppler if growth is discordant or restricted; standard booking bloods, and a glucose tolerance test given the raised diabetes risk.
- Monochorionic twins: ultrasound every 2 weeks from 16 weeks to screen for TTTS and TAPS, assessing deepest vertical pool of liquor in each sac, bladder visibility, growth and Dopplers (umbilical artery, and middle cerebral artery peak systolic velocity for TAPS). These women should be booked at, or referred to, a unit with fetal-medicine support.
- Anaemia: check haemoglobin and treat with iron; the iron and folate demand is higher.
- Pre-eclampsia prevention: offer low-dose aspirin from 12 weeks to those with additional risk factors, in line with hypertension-in-pregnancy guidance — see hypertension-in-pregnancy and pre-eclampsia-and-hellp.
- Anomaly screening: structural anomalies are commoner; the detailed anomaly scan is performed, and aneuploidy screening is interpreted with chorionicity in mind (in monochorionic twins the two fetuses share a karyotype risk).
- Discordant growth, abnormal Doppler, polyhydramnios/oligohydramnios sequence or membrane changes should trigger urgent fetal-medicine referral — these signal that the pregnancy is no longer "uncomplicated".
In the South African system, an uncomplicated dichorionic twin pregnancy can be co-managed at a well-resourced district/regional facility, but all monochorionic twins, and any complicated multiple, belong at regional/tertiary level with ultrasound and neonatal capacity. Know your referral pathway before you need it.
Figure J23.2 — Antenatal management roadmap for uncomplicated multiple pregnancy, linking first-scan mapping, chorionicity-specific surveillance, planned birth windows, referral level and ineffective routine interventions to avoid.
Management
Antenatal management of the uncomplicated multiple
The aims are to detect emerging complications early, optimise maternal health, and plan a safe, well-staffed delivery. Beyond the surveillance above:
- Nutrition and supplements: adequate iron and folic acid; counsel on the higher calorie and protein needs. See pregnancy-nutrition.
- Counsel on preterm labour: teach symptom recognition and ensure rapid access. There is no evidence that routine bed rest, prophylactic tocolytics, prophylactic cervical cerclage or routine progesterone reduce preterm birth in unselected twins, and these should not be offered routinely; reserve cerclage/progesterone for specific indications as in cervical-cerclage and progesterone-in-pregnancy.
- Corticosteroids: a single course of antenatal corticosteroids accelerates fetal lung maturity and is given when preterm birth is anticipated within 7 days (threatened preterm labour, planned early delivery), exactly as for singletons — see preterm-birth-and-pprom. Do not give repeated speculative courses.
- Magnesium sulphate for neuroprotection should be offered when very preterm birth (broadly <30 weeks) is imminent.
Timing of delivery
Continuing a multiple pregnancy too long raises the stillbirth risk, so planned birth is offered before term in a gestation-specific window. Working figures consistent with current guidance:
| Type | Planned birth (uncomplicated) |
|---|---|
| Dichorionic diamniotic | by ~37+0 to 37+6 weeks |
| Monochorionic diamniotic | by ~36 weeks (with a steroid course) |
| Monochorionic monoamniotic | by ~32–34 weeks, by caesarean |
| Triplets / higher order | earlier, by caesarean |
Confirm the exact threshold against the SA Maternity Guideline (NDoH, 2024) and local protocol; the principle — MCMA earliest and by caesarean, MCDA earlier than DCDA, DCDA latest — is the part to retain.
Mode of delivery and the conduct of vaginal twin birth
Mode of delivery for diamniotic twins depends chiefly on the presentation of the first (leading) twin and on chorionicity. Vaginal birth is appropriate and recommended for uncomplicated diamniotic twins where the first twin is cephalic, provided there is no other indication for caesarean and the unit can deliver the second twin safely. The presentation of the second twin does not by itself dictate caesarean, because the second twin can be delivered by breech extraction or by internal podalic version after the first is born.
Indications that favour caesarean include: non-cephalic first twin; monoamniotic twins (always caesarean); conjoined twins; the usual singleton indications (placenta praevia, previous classical caesarean, etc.); and significant fetal compromise. Higher-order multiples are delivered by caesarean.
Conducting a planned vaginal twin delivery — the safe drill:
- Where and who. Deliver in a facility with theatre immediately available, two neonatal resuscitation stations with two resuscitation teams, an anaesthetist informed, and a senior obstetrician present or immediately on call. Establish good IV access (two large-bore cannulae) and send blood for group-and-save/crossmatch — anticipate PPH.
- Monitoring. Continuous CTG of both twins in labour, with clear identification of each trace (twin 1 / twin 2); use a fetal scalp electrode on the leading twin if external traces cannot be reliably separated. See ctg-interpretation and fetal-monitoring-methods.
- Analgesia. Epidural is recommended — it provides effective analgesia and, importantly, allows rapid operative intervention or internal manipulation of the second twin without delay. See labour-analgesia.
- First stage and delivery of twin 1. Manage labour as usual with the partogram-use/Labour Care Guide; augment with oxytocin for inadequate progress only with care given over-distension. Deliver the cephalic first twin normally.
- The interval — the critical step. After twin 1 is born, immediately perform an abdominal (and, if needed, vaginal) examination to determine the lie and presentation of twin 2, and confirm its heart rate. Stabilise the lie to longitudinal — by gentle external manipulation under ultrasound guidance if available.
- If longitudinal cephalic: await descent and deliver, rupturing the membranes only once the head is fixed in the pelvis.
- If longitudinal breech: proceed to assisted breech delivery / breech extraction.
- If transverse/oblique: perform internal podalic version (grasp a fetal foot, bring it down) followed by breech extraction, done by an experienced operator.
- Oxytocin infusion is often started to maintain contractions if they wane after the first birth.
- Delivery interval. There is no fixed maximum, but continuous monitoring of twin 2 is mandatory because the risk of cord prolapse, abruption (as the uterus shrinks), and fetal compromise rises after the first birth. Expedite delivery promptly for any non-reassuring trace.
- Third stage — anticipate haemorrhage. Give active management with oxytocin, and because uterine over-distension predisposes to atony, have additional uterotonics ready and a low threshold for an oxytocin infusion. This is a high-risk PPH setting — see postpartum-haemorrhage.
Emergency within the twin delivery — escalate without hesitation:
If the second twin develops a sustained fetal bradycardia, cord prolapse, or there is suspected abruption, and vaginal delivery is not imminent → declare an emergency, call for senior help and theatre, and deliver by caesarean of the second twin. A "combined" delivery (vaginal twin 1, caesarean twin 2) is an accepted, sometimes life-saving outcome — do not persist with attempts at vaginal delivery of a compromised, undeliverable second twin.
Locked twins / interlocking (rare; classically breech first twin + cephalic second) is an obstetric emergency presenting as obstructed delivery after the first twin's body is born — call for senior help immediately and prepare for caesarean.
Figure J23.3 — Vaginal twin birth drill, from candidate selection and labour-ward safety scaffold through second-twin presentation management, emergency caesarean triggers and third-stage haemorrhage prevention.
Postnatal care
Watch for delayed PPH, support feeding of two infants (twin breastfeeding is achievable and should be encouraged — see infant-feeding), screen for maternal mental-health strain, and offer effective postpartum-contraception before discharge. Document chorionicity and any neonatal concerns clearly in both babies' records.
Red flags / pitfalls
- Failing to fix chorionicity in the first trimester. This is the cardinal error. If a woman books late and chorionicity is uncertain, manage as monochorionic and refer. Never label a twin pregnancy "low risk" before chorionicity is known.
- Treating a monochorionic pair as if it were dichorionic — under-surveilling for TTTS/TAPS and missing the 2-weekly scans. Monochorionic twins need a fetal-medicine-capable unit.
- Dating off the smaller twin, mislabelling an early growth-restricted fetus as just "small for dates."
- Inconsistent twin labelling between scans, so that a Doppler/growth abnormality cannot be tracked to the right fetus.
- Attempting vaginal birth without the full safety scaffold — two neonatal teams, theatre ready, senior obstetrician, anaesthetist, IV access, crossmatch, continuous dual CTG. The second twin is where things go wrong.
- Forgetting that the uterus is over-distended → high atony/PPH risk; have active third-stage management and extra uterotonics ready.
- Persisting with vaginal delivery of a compromised second twin instead of moving to caesarean — recognise the indication for a combined delivery early.
- Routine interventions that do not work — bed rest, prophylactic tocolysis, routine cerclage or progesterone in unselected twins. Do not offer them as "to be safe."
- Single intrauterine fetal death in a monochorionic pair is an emergency for the survivor (acute feto-fetal transfusion → death or neurological injury) — urgent fetal-medicine referral, not reassurance.
Evidence anchors
- SA National Integrated Maternal and Perinatal Care Guideline (NDoH, 2024) — the South African source of truth for booking level, antenatal surveillance schedule, referral pathway and delivery planning for multiple pregnancy; confirm exact gestational thresholds locally.
- RCOG Green-top Guideline No. 51 — Management of Monochorionic Twin Pregnancy — chorionicity determination, monochorionic-specific surveillance (TTTS, TAPS, sFGR), and timing of delivery.
- NICE NG137 — Twin and triplet pregnancy in the antenatal period (current at verification) — first-trimester chorionicity/dating, surveillance intervals, timing of planned birth; standard recommendations on antenatal care of multiples.
- NICE NG235 — Intrapartum care (2023) and NICE NG229 — Fetal monitoring in labour (2022) — continuous dual CTG and intrapartum care principles applied to twins; pairs with the WHO Labour Care Guide (2020).
- RCOG GTG 74 — Antenatal corticosteroids and magnesium sulphate for neuroprotection — for anticipated preterm birth.
- RCOG GTG 52 — Prevention and Management of Postpartum Haemorrhage — over-distended uterus is a major atony risk; active third-stage management, early uterotonics and tranexamic acid (WOMAN trial, Lancet 2017) within 3 hours of PPH onset.
- NICE NG133 — Hypertension in pregnancy (2019) — low-dose aspirin from 12 weeks where additional risk factors are present.
- Saving Mothers / NCCEMD (latest triennium) — obstetric haemorrhage and hypertension remain leading South African maternal-death causes; the over-distended twin uterus sits squarely in the haemorrhage risk pool.