1 of 35

Multifetal Gestation

CASE 27-year-old, G1P0, GA 14 weeks, presents with a diagnosis of twin pregnancy

​

2 of 35

Objectives

OBGYN Clerkship Session Level Objectives

SLO 11: Multi-Fetal Gestation

  • Differentiate the features of monozygotic, dizygotic, multi-zygotic gestation.
  • Counsel a patient on the complications of multifetal gestation.
  • Discuss enhanced monitoring requirements of a multifetal gestation compared to singleton pregnancy.

3 of 35

Background

Definitions

​

​

ZYGOSITY: The number of distinct embryos

​

CHORIONICITY: The number of placentas

​

AMNIONICITY: The number of distinct amniotic sacs

​

​

DISCUSS�What do the colloquial terms “identical” versus “fraternal” twins refer to, medically speaking?

​

​

___________________________________________________

​

​

4 of 35

Dizygotic vs Monozygotic

  • Dizygotic (two distinct eggs with two distinct sperm)
    • Dichorionic diamniotic
  • Monozygotic (one egg and one sperm that split at different time points)
    • Dichorionic diamniotic – 20-30% of MZ
    • Monochorionic diamniotic
    • Monoamniotic – 1% of MZ

5 of 35

Monozygotic Twinning -

the earlier you split, the less you share

  • Dichorionic twins – 0 to 4 days
  • Monochorionic diamniotic twins – 4-8 days
  • Monoamniotic twins – 8-12 days
  • Conjoined twins – 13 days or greater

6 of 35

Monozygotic Twinning

7 of 35

Background

Case 1:

​

27-year-old, G1P0, GA 14 weeks, presents with a diagnosis of twin pregnancy.

​

​

​

8 of 35

History

​

27-year-old, G1P0, 14 weeks GA, presents with a diagnosis of twin pregnancy

What do you want to know on history?

  • Targeted HPI question
  • Hint: Think risk factors, clinical signs/symptoms

​

What will you look for on physical examination?

What will you find different for investigations?

​

​

​

​

9 of 35

History

​

27-year-old, G1P0, 14 weeks GA, presents with a diagnosis of twin pregnancy

Theories on the Causes of Twinning

​

Monozygotic

​

  • Slight increase with maternal age
  • Typically random
  • May increase with Artificial Reproductive Technologies�e.g. IVF

Dizygotic

  • Double ovulation – may be inherited
  • Increases with maternal age up to ~35y
  • Hormonal induction �e.g. clomiphene, letrozole

10 of 35

History

​

27-year-old, G1P0, 14 weeks GA, presents with a diagnosis of twin pregnancy

Clinical Signs of Multiple Pregnancy

​

▪ Significant hyperemesis

▪ Earlier and More weight gain

▪ Fetal movement felt at earlier gestation

▪ Large for dates

▪ Multiple FHRs auscultated

▪ Multiple fetal parts on clinical exam

​

Lab :

▪ Higher B- HCG for gestational age

▪ Higher placental analytes (eg PAPPA , MSAFP etc) for GA

​

​

B-hCG Rule of 10s - SINGLETON

10 IU at the time of missed menses

100,000 at 10 weeks GA (PEAK)

10,000 at term

11 of 35

CASE 1

​

27-year-old, G1P0, 14 weeks GA, presents with a diagnosis of twin pregnancy

​

​

Dating ultrasound at 7 weeks noted two distinct fetal heart rates

Repeat ultrasound booked at 12 weeks to determine number of placentas

​

CONCLUSION OF ULTRASOUND:

2 placentas and 2 amniotic sacs

​

WHAT TYPE OF TWINS IS THIS?

  1. monochorionic monoamniotic twins (MCMA)
  2. monochorionic diamniotic twins (MCDA)
  3. dichorionic diamniotic (DCDA)

​

THIS MEANS THEY ARE:

  1. monozygotic
  2. dizygotic
  3. can be either

​

​

12 of 35

Monozygotic embryo splitting

TWIN TYPE

TIMING OF SPLITTING (days)

DCDA

≤ 4

​

MCDA

4 - 8�

MCMA

8 - 12

CONJOINED

> 12

13 of 35

CASE 1

​

27-year-old, G1P0, 14 weeks GA, presents with a diagnosis of twin pregnancy

​

If monozygotic, splitting of the embryo occurred at _________ days.

�If dizygotic, there were always two distinct embryos.

​

​

​

The patient states she has had ‘wicked’ morning sickness and her BhCG is 168,000. Other than this she is doing well and your history was unremarkable aside from the ultrasound diagnosis of twin pregnancy. The patient states: WOW! Does this mean they are identical?

​

What is your response? ___________________________

​

​

​

​

14 of 35

Multiple Choice Question

Dizygotic twins share which of the following:

​

  1. The same DNA
  2. The same sex
  3. The same placenta
  4. The same parents

15 of 35

Diagnosis

ULTRASOUND IS REQUIRED TO MAKE A DIAGNOSIS

​

  • Ideally between 11-14 weeks
  • Number of placental masses
  • Thickness membrane dividing sacs ( ≥ 2 mm)
    • Lambda sign = Dichorionic, diamniotic
    • T sign = Monochorionic, diamniotic
  • Presence of intervening membrane
    • If no membrane between two pregnancies = monochorionic, monoamniotic
  • Fetal sex

​

16 of 35

DICHORIONIC PREGNANCY

  • Thick layer of chorion can be identified around each gestational sac
  • Thin amnion seen around each sac
  • Lambda sign

17 of 35

​

  • Thin amnion encircles each fetus
  • Chorion surrounds both fetuses together
  • T sign

​

MONOCHORIONIC DIAMNIOTIC PREGNANCY

18 of 35

The truth about Multiples

Twin, triplet and higher order multiple pregnancies are not ‘fun’ for the patient or obstetrician.

​

Multiple pregnancy is a complication and carries increased obstetrical and fetal risks.

19 of 35

Pregnancy Physiology

List 3 physiologic changes that occur in pregnancy, but are more exaggerated with a twin pregnancy:

​

  1. _____________________________
  2. _____________________________
  3. _____________________________

​

20 of 35

Pregnancy Physiology

List 3 physiologic changes that occur in pregnancy, but are more exaggerated with a twin pregnancy:

​

  1. cardiac output increase
  2. hypervolemia
  3. insulin resistance

​

21 of 35

Pregnancy Risks for all multiple pregnancies

MULTIFETAL GESTATION INCREASES PREGNANCY COMPLICATIONS AND RISK:

​

↑ Rate of Spontaneous Abortion

↑ Congenital Anomalies (x2)

↑ Iron Deficiency Anemia

↑ Hyperemesis Gravidarum

↑ Gestational Hypertension

↑ Gestational Diabetes

↑ Acute Fatty Liver of Pregnancy

↑ Pruritic Urticarial Papules and Plaques of Pregnancy (PuPPPs)

↑ Preterm Birth (both preterm labour and iatrogenic) - 40-50% of twin pregnancies

↑ Low Birthweight

↑ Placental Abruption

↑ Operative Delivery

↑ Postpartum Hemorrhage

↑ Venous Thromboembolism

​

​

​

​

22 of 35

Risk of Fetal Mortality

  • Monoamniotic twins – 50-60%
  • Monochorionic diamniotic twins – 25%
  • Dichorionic twins – 9%

23 of 35

Management

​

27-year-old, G1P0, 14 weeks GA, presents with a diagnosis of twin pregnancy

​

How should you manage patients?

Some centres consider Dichorionic/Diamniotic Twins as a ‘moderate risk’ pregnancy and can be followed by Midwifery or Family Medicine unless there are complications.

​

At other centres all multiples are considered ‘high risk’ and are to be followed by Obstetrician

​

Monochorionic pregnancies are often very high risk and require expertise of a Maternal-Fetal Medicine (MFM) specialist

​

​

24 of 35

Management

​

27-year-old, G1P0, 14 weeks GA, presents with a diagnosis of twin pregnancy (DCDA)

​

How should you manage a twin pregnancy?��GENERAL CONSIDERATIONS

  • Diet (increase iron 30mg/day, folic acid 1mg/day, extra 300kcal/day compared to singleton pregnancy)
  • Counsel on maternal and fetal complications
  • Offer prenatal aneuploidy screen (unique for multiples) and chorionicity ultrasound (10-14 weeks)
  • Anatomy scan (and cervix length) at 18-22 weeks (+ fetal ECHO if monochorionic)
    • Monochorionic ultrasounds every 2 weeks starting at 16 weeks
    • Dichorionic ultrasounds every 3-4 weeks starting at 24-25 weeks
  • Work modification at 20-24 weeks can be considered

​

​

25 of 35

Practice:

TWIN TO TWIN TRANSFUSION SYNDROME

CASE 2: What if the patient was actually found to have a MONOCHORIONIC pregnancy?

�What potential complications are unique to MONOCHORIONIC twins?

Twin to Twin Transfusion Syndrome

Large anastomoses exist with an artery connected to a vein on the surface of the placenta

These are large arterio-venous connections which transfer nutrients and red cells from the donor to the recipient

This may result in the twin oligohydramnios-polyhydramnios sequence

Occurs in 10-15% of MCDA

Different treatment options, such as laser ablation of anastomotic vessels (preferred)

​

26 of 35

Monochorionic specific risks

Twin Anemia Polycythemia Sequence (TAPS)

  • Essentially atypical TTTS
  • MCA systolic velocity to assess for anemia:�Recipient < 1.0 MoM, Donor > 1.5 MoM
  • Occurs via small connecting vessels
  • Prevalence 4-5% monochorionic pregnancies
  • Risk can occur after ablation for TTTS or spontaneously
  • Tx: laser ablation, selective reduction, transfuse 1 twin and phlebotomize other

Selective Fetal Growth Restriction (sFGR)

  • Uneven sharing of the placenta resulting in one twin being growth restricted
  • 25% of monochorionic twin pregnancies

Twin Reverse Arterial Perfusion Sequence (TRAP)

  • One twin anencephaly and heart but stays living as donor
  • 2.5% prevalence, 50% mortality rate
  • Tx: laser ablation of acardiac twin’s vasculature

27 of 35

MONOCHORIONIC TWINS COMPLICATIONS

28 of 35

What is this unique complication?

Cord entanglement can only occur in which type of twins?

29 of 35

Management

​

Timing of Delivery

​

When should you plan for delivery?

​

Dichorionic diamniotic: 37 - 38 weeks

​

Monochorionic Diamniotic: 36 - 37 weeks

​

Monochorionic Monoamniotic: 32 - 33 weeks

​

​

30 of 35

Practice

CASE 3:

​

The diagnosis of twin pregnancy was missed at the patient’s dating ultrasound. She is now presenting for her anatomy scan and 2 fetuses are seen. It is too late to clearly see any insertion of the amnion (Lambda or T-sign) and therefore this cannot be used for diagnosis. The technologist can see clearly, however, that one fetus has male sex genitalia and one has female sex genitalia. This twin pregnancy is:

​

​

  1. Monochorionic monoamniotic
  2. Monochorionic diamniotic
  3. Dichorionic diamniotic
  4. Dizygotic diamniotic

31 of 35

Management Summary

Dichorionic Diamniotic Twins

​

  • Determine chorionicity at 11 - 14 weeks
  • Offer prenatal screening
    • FTS with Nuchal Translucency at 11-13+6 weeks
    • NIPS > 10 weeks
  • Anatomy ultrasound at 18 - 22 weeks
  • Growth surveillance ultrasound q4 weeks
  • Cervical length assessment at time of anatomy scan, continue if risk factors for preterm birth
  • Delivery 37 - 38 weeks

​

32 of 35

Management Summary

Monochorionic Diamniotic Twins

​

  • Determine chorionicity at 11 - 14 weeks
  • Offer prenatal screening
    • FTS with Nuchal Translucency at 11-13+6 weeks
    • NIPS > 10 weeks
  • Surveillance for TTTS/Growth starts at 16 weeks
  • Anatomy ultrasound at 18 - 22 weeks
  • Fetal Echo 18 - 22 weeks
  • Growth surveillance ultrasound q2 weeks
  • Cervical length assessment at time of anatomy scan, continue if risk factors for preterm birth
  • Delivery 36 - 37 weeks

​

33 of 35

Management Summary

Monochorionic Monoamniotic Twins

​

  • Determine chorionicity at 11 - 14 weeks
  • Offer prenatal screening
    • FTS with Nuchal Translucency at 11-13+6 weeks
    • NIPS > 10 weeks
  • Surveillance for TTTS/Growth starts at 16 weeks
  • Anatomy ultrasound at 18 - 22 weeks
  • Fetal Echo 18 - 22 weeks
  • Growth surveillance ultrasound q2 weeks
  • Increased daily fetal monitoring starting at 24-26 weeks (inpatient can be considered)
  • Administer steroid prophylaxis prior to delivery
  • Delivery by cesarean section 32 - 33 weeks

​

34 of 35

Resources

Interested in learning more? Check out these articles!

​

​

​

•SOGC#428: Management of dichorionic twin pregnancies (2022)

•SOGC#440: Management of monochorionic twin pregnancies (2023)

•Williams Obstetrics 26e, Chapter 48

​

�

35 of 35

References

THANK YOU to slide authors:

Dr Sue Chandra

Dr Sheryl Choo

Dr Bruno Svajger