Multiple Gestations Flashcards
A diagnosis of a multiple gestation is made when one well-defined gestational sac with ________ yolk sacs or other embryonic structures are present or more than one well-defined GS with a YS or other embryonic structures is present in each GS.
The sonographer must exercise caution in diagnosing multiple gestations and the ________ of multiple gestations that is present at the time of the U/S exam.
2
Type
_______ (“identical”) - 1 egg, 1 sperm meet/join to form a zygote. This becomes a singleton pregnancy. However, if that 1 zygote splits into 2 equal zygotes, it now becomes a twin pregnancy with the same set of chromosomes in each zygote, so it’s identical twins. These are called monozygotic twins (1 zygote splits to form 2 zygotes)
Monozygotic Twin type more prevalent is the Monozygotic-_______ Twin
_______ (“Fraternal”) - 2 sperm meet 2 eggs and 2 zygotes are formed. Each zygote has their own individual set of chromosomes, therefore fraternal, or non-identical twins (although they may be the same gender)
Dizygotic twins can be familial, and it’s common to hear from patients that other members of their families are twins
Multiple Pregnancy/Multifetal pregnancy
- The presence of more than one fetus in the gravid uterus is called _______ pregnancy
- Two fetuses (_______)
- Three fetuses (_______)
- Four fetuses (_______)
- Five fetuses (_______)
- Six fetuses (_______)
Monozygotic Dizygotic Dizygotic multiple twins triplets quadruplets quintuplets sextuplets
_______ Twins = 1 egg, 1 sperm, 1 zygote the different type of twin result is directly related to when the zygote separates/splits occurs
_______ twins = 2 eggs, 2 sperm, 2 zygotes; no sep/splitting
Monozygotic
Dizygotic
This Twin type and zygote separation occurs 8% of all twins.
Monozygotic Twins (Dichorionic, Diamnionic)
This Twin type and zygote separation occurs 20% of all twins and is the most common type of MONOZYGOTIC twin.
Monozygotic twins (Monochorionic, Diamnionic)
This twin type and zygote separation occurs less than 1% of all twins.
Monozygotic twins (Monochorionic, Monoamnionic)
This twin type and zygote separation occurs 72% of all twins and occurs overall more often.
Dizygotic twins (Dichorionic, Diamnionic)
True _____ Twins: 2 -Zygotes But… depending on when the egg splits, may look 2 different ways sonographically
True _______ Twins: 1 -Zygote But…. depending on when the egg splits, become 3 different types of twinning and can be identified sonographically
Dizygotic
Monozygotic
Chorionicity and Amnionicity
_______ and _______ documentation determines type of pregnancy and can easily be determined in 2 periods during gestation: 1st trimester and late 2nd and early 3rd trimesters; 1st trimester is best for accuracy.
_______ refers to the identification of the number of chorionic sacs, and _______ refers to the number of amniotic sacs.
In 1st trimester, 4th-5th weeks, w/transvaginal sonography (TVS), _______ can be determined; appears as sonolucent structures surrounded by hyperechogenic chorion with yolk sac within each chorionic sac.
The number of _______ sacs imaged is correlated with the number of amnions
In the 2nd and 3rd trimesters, accurate establishment of _______ and _______ is difficult although possible. In some instances this becomes absolutely impossible with advancing gestation and moving fetuses.
chorionicity amnionicity chorionicity amnionicity chorionicity yolk chorionicity amnionicity
How to tell Chorionicity/Amnionicity in 1st trimester
1) _______-_______ Twins: 1 chorion, 1 amnion, both embryos within the same amniotic cavity
2) _______-_______ Twins: 1 chorion, 2 amnions with a fetus in each amniotic cavity
3) _______-_______ Twins: 2 chorions, 2 amnions, 2 separate fetuses
May still be _______ twins because the zygote may have split so early after conception that there are 2 distinct sacs.
DO not assume that they necessarily “_______” twins. Each sac contains an embryo with a yolk sac. Each sac has a chorion and an amnion. It clearly looks like two separate sacs.
A thick _______ area which is the membrane is seen between the twins
Monochorionic, Monoamnionic Monochorionic, Diamnionic Dichorionic, Diamnionic monozygotic fraternal echogenic
_______-_______ “Di-Di” - 2 separate chorions and amniotic cavities
Occurs in almost all cases of dizygotic twins (except in very rare cases of fusio) and in 18-36%
DiDi twins have the lowest mortality risk at about 9%, although that is still significantly higher than that of singletons
Dichorionic-Diamniotic twins form when splitting takes place by the _______ day after fertilization
_______-_______ “Mo - Di” - Share the same placenta
Monochorionic twins generally have 2 amniotic cavities
occurs in 60-70% of the pregnancies with monozygotic twins and in 0.3% of all pregnancies.
are almost always monozygotic
Because these twins share the same placenta, and thus have a risk of twin-to-twin transfusion syndrome
Days ____-____
_______-_______ (Mo - Mo) - Share the same amnionic cavity
Occurs in 1-2% of monozygotic twin pregnancies
are always monozygotic
survival rate for monoamniotic twins is somewhere between 50-60%
Monoamniotic twins, as with diamniotic monochorionic twins, have a risk of twin-to-twin transfusion syndrome.
Also, the 2 umbilical cords have an increased chance of being tangles around the babies. Because of this, there is an increased chance that the newborns ma be miscarried or suffer from cerebral palsy due to lack of oxygen.
-Monoamniotic twins occur when the split takes place after the ____ day after fertilization.
_______ twins - When the division of the developing zygote into 2 embryos occurs, 99% of the time it is within 8 days of fertilization. Mortality is highest for conjoined twins due to the many complications resulting from shared organs.
If the division of the zygote occurs later than the ____ days then conjoined twins are usually the result.
Dichorionic, Diamniotic third Monochorionic, Diamniotic 4,8 Monochorionic, Monoamniotic ninth Conjoined 12
How to tells Chorionicity/Amnionicity in 2nd / 3rd Trimester
_______-_______ Twins:
2nd/3rd trimester findings include intertwined fetal parts (arms, legs) an intertwined cords. Color Doppler may be used to demonstrate intertwining of the cords. Spectral Doppler may demonstrates the 2 different HRs of the twins in one clump of intertwined cord
_______-_______ Twins:
A “T” sign will be seen with mono-di twins. The membrane implants flat on the placenta, like a “T” and is thin and difficult to find.
There will only be 1 placenta. Even though there is a membrane separating the twins, they are at higher risk for adverse outcome than dichorionic twins because there is always some degree of shared vascular connections in the 1 placenta of the monochorionic twins. This places monochorionic twins at risk for anomalies, abnormal growth or twin transfusion syndrome, which can result in a poor outcome
_______-_______ Twins: Dichorionic twins may have 2 discrete placentas or 1 fused placenta. If 2 placentas fuse early on, it may be difficult to determine chorionicity. There are some signs that would lead more to a dx of dichorionicity –Where the 2 placentas fuse is where the membrane is attached to the placenta. In the early 2nd trimester it may be possible to see a “lambda,” or chorionic “peak sign” which is diagnostic of dichorionicity. The lambda sign may disappear after 16 weeks. Another hallmark of dichorionic pregnancies is a thick membrane. Since there are 4 layers in a dichorionic membrane it is usually not difficult to visualize, especially when compared to monochorionic membranes. When a patient presents for the 1st sonographic evaluation in late 3rd trimester, it may be impossible to determine chorionicity or amnionicity until after delivery.
Monochorionic-Monoamniotic
Monochorionic-Diamniotic
Dichorionic-Diamniotic
Other sonographic criteria for diagnosing Chorionicity and Amnionicity in the 2nd and 3rd trimesters include:
Determination of fetal gender- different gender indicates _______ twins
The number of placenta(s): 2 separate placentas indicate _______ placentalization. A single or fused placenta is more difficult to evaluate
dizygotic
dichorionic
Monochorionic-Monoamniotic (Mo-Mo) Twin Pregnancy
1 Yolk Sac, 1 Gest Sac, 2 Embryos
_______ in origin
Monochorionnic-Monoamniotic twins have a _______ perinatal mortality rate. Death usually occurs before _____ weeks due to: fetuses within the same _____ (may cause cord entanglement which cuts off blood supply) prematurity, congenital anomalies or twin-to-twin transfusion.
These possibilities should be taken into account when twin pregnancies are detected at the Ultrasound screening between _____ and ____ weeks pregnancy.
This type of twinning represents a very ____ risk pregnancy and intensive monitoring and testing of the babies is required. At times, it is safer to deliver such babies early, some as early as they are viable (_____ to _____ weeks); _____ weeks is often considered “full term” for monoamniotic twins because of the cord risks outweigh the prematurity risks.
Monozygotic high 24 GS 17 20 high 24 28 34
Monochorionic-Diamniotic Twin (Mono-Di) Pregnancy
2 Yolk Sacs, 1 Gestational Sacs, 2 Embryos
______ in origin, IDENTICAL twins, most COMMON type of all twins
____ chorion shared but separated by an amnionic membrane indicating fetuses are in ____ separate amniotic cavities surrounded by ____ chorionic membrane
thin amniotic membrane has to be documented to differentiate it between a Mono-Mono type twin
“____” sign sonographic finding documents the amniotic membrane separation of the 2 fetuses
Monozygotic 1 2 1 T
