zygosity
genetic makeup of twin pregnancy
chorionicity
pregnancy’s placental composition
monozygotic twins (MZ)
fertilization of 1 egg by 1 sperm –> subsequent cleavage of fertilized ovum
dizygotic twins (DZ)
fertilization of 2 separate ova by 2 separate sperm
What type of chorionicity/amniocity do DZ twins develop?
ALWAYS dichorionic diamniotic
- 2 ova
- each blastocyst generates own chorionic and amniotic sacs
How does timing of fertilized ovum cleavage affect placentation of monozygotic twins?
- <72h: di/di
- days 4-7: di/mono (common)
- days 8-12: mono/mono
- > day 13: conjoined
dichorionic diamniotic pregnancy
- 2 gestational sacs
- 2 yolk sacs
- 2 amniotic cavities
- thick dividing membrane
monochorionic diamniotic pregnancy
- 1 gestational sac
- 2 yolk sacs
- 2 amniotic cavities
- thin dividing membrane
monochorionic monoamniotic
- 1 gestational sac
- 1 yolk sac
- 1 amniotic cavity
twin peak sign
triangular projection of tissue seen on U/S that extends beyond chorionic surface of placenta
does not exist in monoamniotic placentation
Why are carriers of multiples are higher risk of GDM?
increase in hPL modifies maternal metabolism
What are the only two obstetric complications that are not more common in multiple gestation?
1) macrosomia
2) post-dates
What 2 factors have the most influence on pregnancy outcome?
1) gestational age at delivery
2) adequacy of fetal growth
What prenatal strategy can have a significant positive impact on pregnancy?
healthy weight gain! especially in early pregnancy
What are recommendations for weight gain in twin pregnancies?
normal weight: 37-54lbs
overweight: 31-50lbs
obese: 25-42lbs
What prophylactic methods are not indicated to prevent PTB in multiple gestation?
1) routine hospitalized bed rest
2) prophylactic tocolysis
3) 17P; vaginal progesterone*
4) cerclage*
5) pessary*
*except in cases of cervical insufficiency
What are antenatal testing recommendations?
unclear
- weekly or twice weekly NSTs or BPPs
- monochorionic twins: @32-34wks
- dichorionic twins: not an indication (ACOG); @34wks (Gabbe)
How is twin growth different from singleton growth?
similar until 30-32wks; growth in twins slows after this
How often are twins evaluated for growth?
U/S growth scans q4wks after 20wks GA
monochorionic: q2wks at 16wks
When should twins be delivered?
uncomplicated dichorionic: 38wks
uncomplicated monochorionic: bw/ 34-37wks
