Multi-fetal Gestation Flashcards
What two factors play a role in the increasing rates of twin/triplet rates?
Older maternal age
Use of reproductive assistance tools
What is the general outline for early embryogenesis from fertilization to blastocyst?
Day 0 = zygote forms from sperm and egg in the ampulla usually
Day 1 = 2 cell stage with 2 blastomeres
Day 3 = morula forms from the blastomeres
- usually 16 cells
Day 4/5 = blastocyst
- usually 56 cells
- 53 cells = trophoblasts which will form the chorion and help develop placenta once implantation occurs
- 3 cells = inner cell mass and become amnion and embryo (embryonic disc)
Day 6/7 = blastocyst ruptures from the zona pellucidum due to proteases in the uterus allowing the blastocyst to implant
Dyzogtic vs monozygotic twins
Dizygotic = 2 oocytes get fertilization by 2 different sperm
- results in two completely separate twin embryo
- 80% of twins
- all are dichorionic and diamniotic
Monozygotic = 1 oocyte get fertilized by 1 sperm but during development of the blastocyst, the zygote splits into two zygotes
- 20% of twins
- earlier splits = more likely to dichorionic and diamniotic
- later splits = more likely to be monochorionic and monoamniotic (almost always day 8 or later)
- increases risk of conjoined twins if split occurs later than day 13*
- can also be monochorionic and diamniotic and is the MOST COMMON* (usually between days 4-8)
it is impossible to have dichorionic and mono amnotic since the split cant occur early enough
Lambda sign “twin peak sign”
Used to differentiation mono/di amnotic and chorionic twins
Is seen best at weeks 10-14
If you see a very dark and obvious lambda sign = dichorionic and diamniotic twins
If you see a very light lambda sign inside a circle = monochorionic and diamniotic twins
If you dont see a lambda sign = monochorionic and monoaminic twins
Twin-twin transfusion syndrome (TTTS)
Occurs in twins that are monochorionic and either mono chorionic and diamniotic
in monochorionic twins, it is possible that venous and arterial anastomosis occurs in the one placenta that both fetuses are sharing
- normally it should be artery -> artery and vein -> vein
- if this occurs, it creates a unidirectional shunt with the artery baby losing blood, causing anemic, growth restriction and oliguric symptoms
- the baby with has the vein in this case becomes polycythemia and experiences hydrops fetalis**
Treatment = laser ablation of the anastomosis ASAP and amino reduction from the hydrops twin
3 types of splits during monozygotic twinning
1) Dichorionic and diamniotic
- the splitting occurs during morula generation (by day 4)
- this results in two distinct trophoblast layers to form allow for twin blastocysts to implant on the uterus and form two separate placentas
- **or if two eggs get fertilized by two sperm
2) Monochoionic and diamniotic
- the splitting occurs after maturation of the trophoblasts (day 5-8), usually during the hatching from the zona pelucidum but before implantation occurs
- this results in one placenta shared between the twins but they can each form their only amnotic sac
3) mono both
- the splitting occurs after implantation (up to week after) and results in both twins sharing both sacs
- if this occurs post day 13 = high risk for conjuoiuned twins
Dizygotic twins vs monozygotic genetics
Dizygotic (“fraternal” twins) = essentially 2 separate siblings since they both share only 50% of DNA from both parents (this is two separate oocytes being fertilized so essentially its two separate pregnancies just occurring at the same time)
- these fetuses will not look the same and can be different sexes (two different sperm)
- 70% of total twin pregnancies are this
Monozygotic (“identical” twin)= are actually twins since they share all genetic information
- these fetuses will look the same and always the same sex (only one sperm)
- this is 30% chance
Ultrasound diagnosis of twins
ACOG recommends at least 1 US by week 22 (usually between 18-22 weeks)
- earlier the better to determine the amniotic and chorionic status
- this makes it more apparent and readily available to prepare for twin pregnancies
Fetal complications in all types of twins
“Vanishing twins” = can see the zygotes developing normally initially but then one loses the ability to thrive and causes still birth
- occurs in the first trimester
Preterm delivery (high rates)
Intrauterine growth restriction (IUGR)
Fetal complication of monochorionic twins
possess all potential complications of dichorionic twins
TTTS
- causes stillbirth/demise of one twin and over growth of the other (often congenital anomalies in the alive twin due to hydrops fetalis)
Fetal complications of mono amniotic twins
possess all complications of dichorionic and monochorionic twins
Cord entanglement and conjoined twins can occur
- occurs more often if the splitting of the blastocyst takes longer than 12 days
Maternal risks of twins
Hospitalization
Increased cardiac output and plasma volume
- very high risk for postpartum hemorrhage
Increased preeclampsia and HTN
Increased gestational diabetes
Increased rates of C-section
Increased nausea and vomiting in pregnancy (NVP)
Maternal mobility is 4.2x more likely in twin pregnancy**
Preterm birth in twins
Almost always seen in twins
Average gestational age in 1 baby = 39 weeks
- in twins = 35 weeks
60% of twin births delivery before week 37
Complications of preterm
- hypothermia
- pulmonary and cardiovascular complications
- glucose dysregulation
- retinopathy of prematurity
- chronic infections
can be iatrogenic induced if the uterus becomes irritated and starts to increase risk to mom
Intrauterine growth restriction
super high risk in preterm delivery
Growth slows down at week 32 with twins and results in risk of failure to thrive (this occurs due to lack of room in the uterus)
- this results in one twin being bigger than the other usually
Treat = ultrasounds, Doppler velocimetry, amnotic fluid assessment, biophysical profiles
often need to induce iatrogenic preterm delivery
**also need to calculate the growth discordance (if present) = (differences in weight)/ larger twins weight). If this is > 20% = growth discordance is present
Twin pregnancy management
Need to focus on specifically
- gestation weight gain
- genetic screening from mother blood or amnotic fluid
- maternal weight gains
- congential anomaly screening
- routine US for growth and placenta appearance
