Study your flashcards anywhere!

Download the official Cram app for free >

  • Shuffle
    Toggle On
    Toggle Off
  • Alphabetize
    Toggle On
    Toggle Off
  • Front First
    Toggle On
    Toggle Off
  • Both Sides
    Toggle On
    Toggle Off
  • Read
    Toggle On
    Toggle Off

How to study your flashcards.

Right/Left arrow keys: Navigate between flashcards.right arrow keyleft arrow key

Up/Down arrow keys: Flip the card between the front and back.down keyup key

H key: Show hint (3rd side).h key

A key: Read text to speech.a key


Play button


Play button




Click to flip

14 Cards in this Set

  • Front
  • Back
Two fertilized ova and two sperm= 2 zygotes. Occurs more frequently with increasing maternal age and with artificial fertilization technology. Fraternal twins. Genetically distinct.
Diamnionic, dichorionic, monozygotic
All MZ twins are “identical twins”. They are genetically identical besides DNS mutations that occur developmentally. Two amnions, two chorions (placentas) and one Zygote that split 1-3 days after fertilization.
Diamnionic, monochorionic, monozygotic
Two amnions, one chorion. Zygote splits day 3-8 when the chorion has already formed.
Monoamnionic, monochorionic, monozygotic
One amnion, one chorion.
Zygote splits day 8-13 when amnion and chorion are already formed.
Zygote splits beyond 13 days. Cranium, thorax, abdomen, pelvis.
Occurs about 1/50,000 births.
Often terminated d/t poor prognosis.
Dizygotic frequency
In United States DZ twins occur about 25/1000 births, representing 80% of all twin births.
Mononzygotic frequency
Have steady worldwide rate of about 4/1000 births, representing 20% of all twin births.
Di-Di: 30%
Di-Mono: 70%
Mono-Mono: 1%
Conjoined: .002-.008%
Twinning factors
Race: 1/100 pregnancies of white women. 1/80 AA. May be due to racial variations in FSH levels of women.
Heredity: Maternal family Hx
Maternal age: first sign of reproductive aging occurs around 37 yo. This represents a time of maximum hormonal stimulation (isolated rise in FSH), which increases rate of double ovulation.
Parity: Increases with paritiy
Fertility drugs: Clomiphine citrate, chorionic gonadotropin, and FSH
Nutrition: Large, tall, heavy women have twins more frequently than small, short, skinny women.
Pituitary gonadatropin: common factor linking race, age, weight, and fertility to multifetal gestation may be FSH levels.
Maternal symptoms
•Excessive wt gain
•Sensation of more than 1 moving fetus
PE exam suspicious of twinning
•Size > dates
•Accelerated wt gain
•More than one heartbeat
•See more than one fetus on U/S
Note: Best to dx twins at 12 weeks, especially b/c it allows great visualization of the chorionicity of this twin pregnancy
oLook for the “twin peaks” sign. There are 2 layers of amnion and chorionic fused together; this suggests diamniotic, dichorionic twins. The twin peaks sign is best sought on sono b/w 10-14 weeks and might disappear after 20 weeks.
oThe Thin T sign identifies diamniotic, monochorionic twins
oRemember: 2 sacs doesn’t always mean there are 2 placentas
Maternal Complication of twins
(Women with multiple gestations are almost 6x more likely to be hospitalized with complications)
-Pre- Eclampsia (2.5 x singleton)
-Abruption (3x more likely) (Tran) ** ACOG says abruption is 8.2 x more likely**
-Anemia (2.5x)
-PTL and delivery (40% greater)
-UTIs (1.5x)
-Greater incidence of Post-partum hemorrhage and intrapartum blood loss in women with multiple pregnancy.
-Greater incidence of Acute fatty liver (1/10,000 in singleton pregnancies; 14% of identified cases of actue fatty liver were twin pregnancies).
-Greater risk of pulmonary embolism
-Recent study showed that 3% of twin pregnancies were complicated by PEP, compared with .5% of singleton pregnancies (ACOG bulletin)
Fetal Complications of twinning:
-PTB (median GA is 36 wks) PTB occurs in 43.6% of all twin births, compared with 5.6% in singleton pregnancies.
-Higher risk for cerebal palsy; 4x more often in twin than singleton pregnancies
-Twins are more likely to be SGA, which is associated with an increase in the risk of perinatal morbidity and mortality and is more common in monochorionic twin pregnancies.
-Fetal malpresentation
-Cord prolapse
-Demise of a co-twin (vanishing twin rate of 21% in the 1st trimester;)
-Discordant growth
-Twin-twin transfusion syndrome (only monochorionic twins)
-Risk of death by age 1 year is 7 x higher than singletons
-Increased risk of congenital abnormalities including NTDs, bowel atresia, and cardiac anomalies
Genesis of Monozygotic Twins theories
Evidence suggests that division of the fertilized ovum may result from a delay in the timing of normal developmental events.
*delayed ovum transport through the fallopian tube increases the risk of twinning.
*B/x progestational agents and combination contraceptives decrease tubal motility, delayed tubal transport and implantation are believed to increase the risk of twinning in pregnancies conceived in close temporal proximity to contraceptive use
*Minor trauma to the blastocyst during ART may lead to the increased incidence of monozygotic twinning