Rate – geographical variation
• Genetic component
• Maternal factors – age 35–39
• Multiparity – raised BMI
• Non-identical twins
Dizygotic (6.5/1000)
• Always 2 placentae
Monozygotic (3.5/1000)
• Timing of division of embryo (E) in
relation to stage of development
• Chorion (Ch)→ Amnion (A)→ Fetus (F)
1–4 day embryo
• 2 chorion,
• 2 amnion, and
• 2 fetuses
4–7 day embryo
• 1 chorion,
• 2 amnion, and
• 2 fetuses
8–12 day embryo
• 1 chorion,
• 1 amnion, and
• 2 fetuses
> 12 days embryo
• 1 chorion,
• 1 amnion, and
• conjoint fetuses
Background
• Chorionicity: the number of chorionic (outer) membranes that surround babies in a multiple pregnancy,
indicating whether babies share a placenta. In monochorionic (MC) pregnancies babies share one
placenta; in dichorionic pregnancies (DC) there are two placentas; in trichorionic triplet pregnancies each
baby has a separate placenta.
• Amnionicity: the number of amnions (inner membranes) surrounding babies in a multiple pregnancy.
Pregnancies with one amnion (so that all babies share an amniotic sac) are monoamniotic (MA); with
two amnions are diamniotic (DA); and with three amnions are triamniotic.
• Zygosity: pregnancies are either monozygous (arising from one fertilized egg) or dizygous (arising from
two separate fertilized eggs). Monozygous twins are identical; dizygous twins are non-identical.
Risks or complications
• Maternal risks:
Hyperemesis, anaemia, PTL, PET/PIH, placenta praevia,
APH, PPH, hydramnios
• Fetal risk:
Miscarriage, congenital abnormalities, loss of one twin,
IUGR, TTTS, TRAP
• PNM 3 times higher in MC compared to DC
History and examination
• History – hyperemesis, assisted conception
• Examination – large for dates
Investigations
• First trimester USS when CRL measures 45 mm to 84 mm (at 11 weeks 0 days to 13 weeks 6
days) to estimate gestational age, determine chorionicity, and screen for Down syndrome. Use
the largest baby to measure gestational age.
• Assign nomenclature to babies in twin and triplet pregnancies and document this in the notes to
ensure consistency throughout pregnancy.
Chorionicity – Determine chorionicity using the number of placental masses, the lambda or T-sign,
and membrane thickness.
• Lamda sign is formed by a tongue of placental tissue within the base of dichorionic membranes.
• For women presenting after 14 weeks 0 days, use all of the above features and discordant fetal
sex.
• Do not use 3D USS to determine chorionicity.
Problems determining chorionicity:
• Poor transabdominal views because of a retroverted uterus or high BMI – use TVS.
• If it is not possible to determine chorionicity seek a second opinion or refer to a HCP competent
in determining chorionicity by USS, ASAP.
• If it is still difficult after referral, manage as MC until proved otherwise.
Maternal care
• Book at 10 weeks.
• Higher incidence of anaemia – Perform a FBC at 20–24 weeks to identify a need for
early supplementation with iron or folic acid, and repeat at 28 weeks.
• Hypertension – Measure BP and test urine for proteinuria at each appointment.
• 75 mg of aspirin daily from 12 weeks until the birth of the babies if they have one or
more of the following risk factors for hypertension: * First pregnancy. * ≥ age 40
years or older. * Pregnancy interval of more than 10 years. * BMI of 35 or more
at first visit. * Family history of PET.
Fetal anomaly and growth scans
• Structural abnormalities (anomaly scan at 18+0 to 20+6 weeks) – Consider scheduling scans slightly
later.
• Serial growth scans:
* MC – Clinic appointment and scan FFTS starting at 16/40 – every 2 weeks up to 24 weeks; 28
weeks, 32 weeks, 34 weeks, and 36 weeks.
* DC – Scan starting at 20 weeks – every 4 weeks. Clinic appointment at 16 and 34 weeks.
• Monitor for IUGR:
* EFW discordance using 2 or more biometric parameters at each USS from 20 weeks.
* Aim to undertake scans at intervals of < 28 days.
* Consider a 25% or greater difference in size between twins or triplets as a clinically important
indicator of IUGR and refer to FMU.
• Fetal Growth: USS – 4 weekly for DC; 2 weekly for MC.
• Do not use: abdominal palpation or SFH measurements to predict IUGR; umbilical artery Doppler
ultrasound to monitor for IUGR or birth weight differences.
Preterm birth (PTB)
• Predict the risk of PTB
* Higher risk if history of a spontaneous PTB in a previous singleton pregnancy.
* Do not use cervical length (with or without fetal fibronectin) routinely to predict
the risk of PTB.
* Do not use the following to predict the risk of PTB: fetal fibronectin testing
alone; home uterine activity monitoring.
• Preventing PTB – do not use the following routinely to prevent spontaneous PTB:
bed rest at home or in hospital; IM or vaginal progesterone; cervical cerclage; oral
tocolytics.
• Untargeted corticosteroids – do not use single or multiple untargeted (routine)
courses of corticosteroids.
Delivery – mode and time
Uncomplicated twin pregnancies
• About 60% of twin pregnancies result in spontaneous birth before 37 weeks.
• Continuing twin pregnancies beyond 38 weeks increases the risk of fetal death.
• Offer elective birth at:
* 36 weeks for MC twin pregnancies, after a course of corticosteroids.
* 37 weeks for DC twin pregnancies.
Uncomplicated triplet pregnancies
• About 75% of triplet pregnancies result in spontaneous birth before 35 weeks.
• Continuing triplet pregnancies beyond 36 weeks increases the risk of fetal death.
• Offer elective birth from 35 weeks, after a course of corticosteroids.
If elective birth is declined, offer weekly appointments with an USS, fortnightly fetal growth scans, and
weekly biophysical profile.
Mode of delivery
Vaginal delivery
• Cephalic/cephalic, cephalic/breech presentations.
Indications for CS:
• MCMA pregnancies – risk of cord entanglement – best delivered at 32/40 by CS,
after corticosteroids.
• Breech/breech, breech/cephalic presentations.
• Any complications – PET, IUGR.
Intrapartum care
• Delivery in maternity unit – experienced doctor/midwife, operative theatres/anaesthetist,
paediatric staff, blood transfusion facilities, USS available.
• Continuous CTG ´ 2 – abdominal/fetal scalp electrode.
• Epidural anaesthesia, IV access, cross match.
• Syntocinon can be used for augmentation.
