RANZCOG q Flashcards
a. Describe the relationship between zygosity and chorionicity in twin pregnancy. (3 marks, diagrams are acceptable)
Zygosity = number of fertilized ova resulting in pregnancy Monozygous = 1 egg, 1 sperm, 1 zygote that subsequently splits to create twins Dizygous = 2 eggs, 2 sperm, 2 zygotes
Chorionicity = number of chorion – placenta and membranes Monochorionic = 1 placenta Dichorionic = 2 placentae
Dizygous twins always become dichorionic, diamniotic
Monozygous - depends on the stage of development at which inner cell mass divided
If division occurs:
<3 days – DCDA
4-7 days – MCDA
8 days of more MCMA
You see a 28 year old primigravid woman with light bleeding at 8 weeks gestation. An ultrasound shows she has dichorionic diamniotic twins.
b. Outline the key events you should recommend for antenatal care in this pregnancy. (5 marks)
- Further history – LMP. Obstetric and general medical history.
- Antenatal bloods – as per singleton
- 1st trimester screening – as per singleton
- Supplementation – high dose folate (5mg), iron and iodine
- Counselling re: risks to mother and fetuses
- Planning care – shared care - secondary care (obstetric) with midwife appropriate
- Morphology USS 20/40 including detailed cardiac views
- 4-weekly growth USS from 20/40, shorter intervals if abnormality detected
- 28/40 – GTT, FBC and iron studies
- Each visit – vigilance HTN/PET – BP and urine
- Delivery planning – gestation depends on maternal and fetal wellbeing. Mode depends on presentation – appropriate to consider NVD if 1st twin cephalic and consider maternal wishes, recommend elective delivery by 38/40 if uncomplicated
She presents in spontaneous labour at 34 weeks gestation. (DCDA twins)
c. Discuss the steps you will undertake in preparing for and performing this particular delivery in order to optimise the outcome. (7 marks)
Planning
- Determine presentation of 1st twin – if cephalic, reasonable to proceed with NVD.
- Setting – timely access to obstetric/anaesthetic staff and operating theatre. Arrange in utero transfer if not suitable NICU/obstetric unit and birth not imminent (may consider short term tocolysis for transfer)
- Inform NICU as twins and preterm
- Ensure equipment
- 1:1 midwifery care
Performing
- IVL and FBC/G&S in early labour
- Regular VE to ensure adequate progress
- IV antibiotics intrapartum as preterm – GBS prophylaxis
- Analgesia – Epidural recommended - if quick recourse to OT or internal manouvres required. Consider maternal wishes.
- Syntocinon indications as per singleton
- CEFM – ensure both twins monitored consider ARM and FSE of 1st twin if required
Delivery
- Paediatric team at delivery
- After delivery of 1st twin – USS available, use to determine position of T2
- If cephalic – stabilize
- If non-cephalic options are ECV/continue labour and IPV/breech extraction – try to avoid rupture of membranes until twin turned
- Consider use of syntocinon to minimize inter-twin delivery interval
- Quick recourse to operative delivery if abnormal CTG – risk 4-10%
- When 2nd twin delivered, active management of 3rd stage and deliver placentae
- Vigilance PPH
(Also- steroids and ?tocolyse)
February 2015: Question 3: Twin Pregnancy
a. Describe the different types of twin pregnancy and how they arise. Where relevant include descriptions of the embryological events and their timing (3 marks)
Monozygotic – arise from splitting of a single embryo (ie one egg, one sperm) – can be di- or monochorionic
o Dizygotic – arise when two eggs have each been fertilized by one sperm at the same time. Are always DCDA
o Dichorionic diaamniotic – either dizygotic (as above) or monozygotic splitting within first 3 days of fertilization. Each have a placenta and amniotic sac
o Monochorionic diamniotic – always monozygotic, splitting between 3-9 days. Share a single placenta, each have amniotic sac
o Monochorionic monoamniotic – always monozygotic, splitting between 9-12 days. Share a placeta and single amniotic sac
o Conjoined twins – always monozygotic, splitting after 12 days. Share a placenta and aminiotic sac and are joined (variable types)
b. Chorionicity is best determined by ultrasound:
i) Using what criteria? (2 marks)
ii) At what gestation? (1 mark)
o Dividing membrane o Twin peak or lambda sign – DCDA o T sign – MCDA o DCDA usually thicker (>2mm) separating membrane o Number of placental masses
ii) 10-14/40
You are reviewing a 34 year old woman in her first pregnancy at 12 weeks gestation. She has had an ultrasound showing she has monochorionic diamniotic twins (MCDA) with no abnormal features detected at first trimester aneuploidy screening.
c. You explain that her pregnancy is at increased risk of complications similar to dichorionic twins but is also at risk of specific monochorionic complications.
i) Briefly discuss 3 specific complications of MCDA twin pregnancies that may occur in this woman (3 marks)
o TTTS (15%) o Caused by inequal sharing of placental blood flow through unidirectional placental anastomoses causing one twin to become donor o Classical type – TOPS (twin oligohydramnios/polyhydramnios sequence) -can cause growth restriction, oligohydramnios, absent bladder, abnormal umbilical artery dopplers in donor and polyhydramnios, cardiac dysfunction and cardiac failure (hydrops) in recipient. Usually occurs in 2nd trimester. Occurs in 10% MCDA. o TAPS (twin anaemia/polycythemia sequence) – very slow transfusion from donor to recipient, so lacks the amniotic fluid discordance and cardiac dysfunction, but can cause significant anaemia and polycythemia reflected by markedly discordant MCA PSV. More common later pregnancy, may not be detected until birth. Occurs in 5% MCDA, and 10% post laser for TOPS.
o TRAPS – Twin reversed arterial perfusion syndrome – 1 twin is acardiac or has non-functioning heart, and other twin becomes ‘pump’. Very poor outcome if untreated, as hydrops can occur in pump twin
o Significant risk >20% of cerebral palsy or other significant neurodevelopmental delay of surviving cotwin if death of the other, due to significant haemodynamic changes at the time of demise
o Discordant growth – usually due to unequal share of placenta and velementous cord insertion but without fluid shifts associated with TTTS. Significant if >25% discrepancy
ii) Outline your management of her pregnancy to enable you to diagnose and/or facilitate appropriate intervention for MCDA specific complications that may occur (5 marks)
o Care under specialist obstetrician, often MFM unit if available
o NT at 12/40 as aneuploidy and NTD screen but also as discordance of NT and CRL increases the likelihood of later diagnosis TTTS (but not diagnostic and insufficient predictive value to use as screening test for this)
o Detailed anatomy scan with good views fetal hearts
o Fortnightly USS from 16/40 for growth, liquor, presence fetal bladder, dopplers including UAPI.
MCA PSV – from 24/40
earlier diagnosis of TTTS and referral to specialist centre likely to improve outcomes
o Patient education to present immediately if sudden increase abdominal girth or breathlessness as signs of polyhydramnios, or signs of preterm labour
o Usually delivery by 36-37/40 due to increased risk of stillbirth despite intensive surveillance. Mode of delivery controversial. Depends on patient’s wishes, can have vaginal birth if twin 1 cephalic and no other obstetric indications CS
o Consider corticosteroids if preterm delivery
At 34 weeks gestation, both twins are cephalic and are appropriately grown with no growth discordancy. The mother has no pregnancy complications.
d. What is the specific fetal risk of vaginal twin delivery in this woman? (1 mark)
Acute transfusion in labour (occurs in up to 10%)
Diagnosis of TTTS
Quintero staging based on Discordancy of Amniotic fluid
• Stage 1
• <20 weeks Twin 1 DVP <2cm, Twin 2 DVP > 8cm
• >20 weeks Twin 1 DVP <2cm, Twin 2 DVP > 10cm
• Stage 2 Absent Bladder in Oligohydramnios twin
• Stage 3 Critical Dopplers in either twin
• Critical Dopplers = Umbilical artery Doppler absent or reversed
• Stage 4 Hydrops in either twin
Stage 5- death of 1 twin
Diagnosis of TAPS
• MCA PSV which are >1.5 MoM AND <1.0 MoM
• There is a risk of TAPS because of small anastomoses that may remain after laser
coagulation (may be right at the edge of the placenta)
Diagnosis of sFGR
- EFW discordancy of >25% OR
* EFW of one twin < 10th centile
When to deliver?
- DCDA
- MCDA
- MCMA
- DCDA 37-38/40
- MCDA 36-37/40
- MCMA 32/40
Definition zygosity
Degree of genetic similarity between each pair
Dizygous- 2 eggs and 2 sperm, typically share approx 50% of genetic material
Monozygous- 1 egg fertilised by 1 sperm which then splits at some stage in early pregnancy
Definition chorionicity
No of placentae in the pregnancy
Risks of twin pregnancy
- Fetal loss- 2% DCDA, 8% monochorionic
- Anomaly
- Preterm birth
- PET
- IUGR
- GDM
- Complicated delivery
- Monochorionic: TTTS (10-15%), TAPS, TRAP, selective IUGR-
