Module 9.1: Fetal Environment Multiple Gestation Flashcards
Multiple gestation pregnancies accounts for how much of all natural pregnancies in Canada? And how much in Alberta?
1% and 3.5% in Alberta
Why has the rate of multiple gestations increased since the 80s? 2
- Delayed childbearing - increased maternal age
- Increased use of assisted reproductive technology
Multiple gestation pregnancies are considered high risk why? 2
Due to increased morbidity and mortality of
1. Fetal
2. Maternal
Multiple pregnancies have how much more risk of higher mortality rate than singleton?
5-10 times
Mothers are at how much more times at risk of severe complications pre and postnatally?
4 times
Why would there be loss of twins? 3
- Spontaneous abortion
- Embryonic malformation
- Non viable pregnancies
What is the twinning rate initially? And why?
Twining rate is higher initially, however one twin may die in early pregnancy and be reabsorbed leaving a singleton
Early u/s shows a large number of pregnancies start out as what?
Twins
What are dizygotic twins?
Fraternal twins
1. Zygote means number of eggs
2. Di = 2 eggs
What are monozygotic twins?
Identical - mono= one egg
What is the percentage of dizygotic in terms of twinning?
70%
What is the percentage of monozygotic in twins?
30%
Of the monozygotic twins how many are di/di?
20%/30%
Of those monozygotic twins how many are mono/di?
70%
What are the percentage of dizygotic twins?
70% or 1/80 rates
What influences dizygotic twins?
Influenced by genetic and environmental factors
What is the genetic mix of dizygotic twins? What is the genetic similarity?
They have their own genetic mix, but their genetic mix is similar to siblings
What influences the risk of dizygotic twins? 4
- Maternal age and parity
- Hereditary
- Racial background
- Pharmaceutical agents
What are 2 things that increase dizygotic twins rate? 2
- Age (either young or late maternal age)
- Parity
What hereditary factors increase chance of dizygotic twins?
Hereditary on maternal side
What is the Asian/ Latin American chances of dizygotic twins?
<8/1000
What is the racial background twinning rate for European countries?
8-12/1000
What are the chances of twinning for racial background in African country?
> 18/1000
What is the birth rate for monozygotic twins?
30% or 1/250 natural births
What influences monozygotic twins?
Random occurrence
What is the genetic variance of monozygotic twins?
Genetically the same
What is the mortality rate of monozygotic twins compared to dizygotic twins?
2X
What is the congenital anomalies rate of monozygotic compared to singletons? (How much more often)
2-3 times more often
What are types of monozygotic twinning? 5
- Identical twins
- Dichorionic- diamniotic
- Monochorionic - diamniotic
- Monochorionic - monoamniotic
- Conjoined twins
What is dichorionic - diamniotic twins? How often does it occur for dizygotic and monozygotic 3
- Occurs with all dizygotic twins and may occur
- Can occurs with monozygotic twins 18-30%
- This is when there is two placentas/ two amniotic sacs
When/ how does dichorionic - diamniotic happen in monozygotic twins? 3
- Morula splits before it implants
- 2 days post fertilization
- Each implants separately resulting in two chorionic sacs
What is monochorionic- diamniotic? How does it occur? When does it occur?
- Two fetuses in separate amniotic sacs a single chorionic sac
- Division occurs at blastocysts stage, after the inner cell mass of the embryo forms
- Day 4-8 post fertilization
How often will monochorionic - diamniotic happens in monozygotic twins?
70%
What is monochorionic - monoamniotic? How often does it happens to monozygotic twins? How does it occur? When does it occur?
- No membrane between fetuses, one placenta
- Happens in 4% of all monozygotic twins
- Division occurs at the embryonic disc stage after the amniotic sac has formed
- Day 8-12 post fertilization
What is the mortality rate for monochorionic-monoamniotic? And why?
Increased risk of mortality due to cord entanglement
What are conjoined twins? When does this happens?
- Incomplete division at embryonic disc stage
- Occurs after day 13 post fertilization
What is the most important ultrasound appearance predictor of pregnancy outcome? When is it best determined?
Chorionicity, and it is beset determined 10-14 weeks
When we assess chorionicity: membranes and placenta, what should we identify? 4
- The number of placentas
- The presence or absence of a separating membrane
- Where the membrane meets the placenta
- Identify the presence of either a twin peak sign or “T” sign
For a DC/DC type of twins, what are the
# of gestational sacs?
# of amniotic cavities
# of embryos per sac
# of yolk sacs
- 2 gestational sacs
- 2 amniotic cavities
- 1 Embryo per sac
- 2 yolk sacs
For a MC/DC type of twins, what are the
# of gestational sacs?
# of amniotic cavities
# of embryos per sac
# of yolk sacs
- 1 gestational sac
- 2 amniotic cavities
- 1 per amniotic sac
- 2 yolk sacs
For a MC/MC type of twins, what are the
# of gestational sacs?
# of amniotic cavities
# of embryos per sac
# of yolk sacs
- 1 gestational sac
- 1 Amniotic cavity
- 2 embryos per sac
- 1 yolk sacs
For a DC/DA what is the chorionicity? 3 (what does it look like, what sign should we see, how should the membrane appear?)
- 2 placentas may appear separate or fused
- Twin peak signs where membrane meets the placenta
- Thick membrane
What is the chrionicity of MC/DA? (how many placentas, what signs, what does the membrane look like)
- 1 placenta
- T sign where membrane meets the placenta
- Thin membrane
What is the chorionicity of MC/MA? (How many placenta, how does the membrane look?
1 placenta
2. No membrane
What does 2 placentas look like? What do they occur with? 3
- Two placentas so close together they look/ appear fused looking like one placenta
- With dizygotic twins there will be 2 separate placentas
- DC/DA
What does a fused placenta look like? And what sign do we look for? 2
- This occurs where two placentas implant close together they may appear fused
- Some placenta will grow up between the membranes creating a “Twin peak sign” also called a Lambda sign
What does one placenta with a membrane looks like? How does it occur?
- Division occurs after implantation will resulting in one placenta forming.
- One placenta with two membranes creates a T sign
What are some clinical indication for scans? 5
- Strong family history
- Large for gestational age
- Increased maternal hCG
- Two or more heart beats heard by one doctor
- Usually first indicated at dating or nuchal translucency (NT) scan
What is the sonographic protocol? (8 steps)
- Identify the number of fetuses present
- Identify the position of both fetuses
- Label the presenting twin (Closest to the cervix) as A and label which side of the mom (uterus) this baby is on (left or right)
- Identify chorionicity/ amnionicity by presence of membrane, number of placenta, presence of twin peak sign or T sign
- Scan each fetus as a singleton and complete all documentation before moving to the next fetus
- Enter biometry measurements into separate calf packages for Fetus A,B, etc.
- Show similar fetal parts to demonstrate multiple fetuses and compare size
- Rule out polyhydraminos (5-10%)
What is the occurrence rate of polyhydraminos for twins?
5-10%
How do you do an AFI on a twin pregnancy? 2
- Measure deepest pocket (DVP), ideally in view of the dividing membrane
- Oligohydraminos is <2cm, Polyhydraminious is >8cm
When does fetal demise happen?
Usually during first trimester but can occur at any time in the pregnancy
What is papyraceus fetus?
The boney remains of the demised fetus
When imaging of the papyraceus fetus on follow up studies what is required?
Sagittal and transverse images
Why would we consider fetal reduction? 2
- There is an increased rate of higher order multiples due to increased use of fertility treatments either with fertility drugs or IVF
- There are much higher rates of prematurity and complications with these multiples
What is offered for fetal reduction?
Feticide to improve outcomes of these pregnancies
What does this image demonstrate?
A vanishing twin
What are the arrows pointing to? From top to bottom
- Chorion
- Amnion
What do both these images represent?
The lambda sign
What does this image demonstrate?
Two separate, distinct, gestational sacs
