Ovulation During Established Pregnancy Resulting

M-1 Coop 2009 Class: Human Development Date: 12/1/05 11:00-12:00 am Lecturer: Dr. Randall Kulhmann Twins and Other Multiples “Double Trouble, Triple Trouble” A. Dizygotic Twins (Dz): Fraternal – (Two fertilized eggs), “Womb mates” – (Same womb, but genetically dissimilar, usually dichorionic/diamniotic) • Incidence 1/80-1/100 pregnancies (INCREASING in frequency in recent yrs.) • Hereditary tendency, tendency in advanced maternal age, reproductive technology advances • Hellin’s Hypothesis (less used due to increasing trends, 1/40-1/80) o 1/80-1/90 for twins o 1/902 for triplets o 1/903 for quadruplets B. Monozygotic (Mz): Identical – (Egg splits after fertilization), genetically identical, phenotypically similar • Incidence 1/250-1/300 pregnancies (CONSTANT for decades) • The earlier the “SPLIT” the better for mom and babies • Chorion gives rise to the placenta, can fuse, • Imbalance in placenta size or sharing can lead to intrauterine growth restriction to one of the twins • Biggest risk is congenitial anastomoses (chorioangiopagus) o TTTS (Twin-Twin Transfusion Syndrome) • Dichorionic/diamniotic – 30% of Mz pregnancies, egg separation before day 3 • Monochorionic/diamniotic – 70% of Mz pregnancies, blastomere separation in 1st week • Monochorionic/monoamniotic – Rare, ICM seperation in 2nd week o Biggest risk is congenitial anastomoses (chorioangiopagus)  TTTS (Twin-Twin Transfusion Syndrome) • Often results in polycythemic/anemic twin pairs • Recipient – polycythemic (too much blood), polyhydramnios, larger • Donor – anemic, oligohydramnios, smaller • Different variations o A-A Artery to Artery (MOST COMMON) o A-V Artery to Venous o V-V Venous to Venous • FLOC-Fetoscopic Laser Oblation of Chorioangiopagus o Method to stop anastomosis o 60% have umbilical cord entanglement (in same amniotic sac), 4% of these actually tie knots

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o Mothers advised to be admitted at 24 weeks and put on monitor and babies will be delivered no later than 32 weeks (40% survival rate for fetus at 24 weeks, put in NICU) Conjoined Twins – Very Rare, incomplete separation of ICM in 3rd week o No increase in chromosomal abnormalities o Organ involvement determines potential for separation o Classified according to conjoined anatomy  Thoracopagus – at thorax, chest  Pyopagus – at sacrum (posteriorly)  Ischiopagus – at pelvis (anteriorly)  Sirenomelic – at extremities  Craniopagus – at head

C. Problems with Multiple Pregnancies & Births • Increase in Premature births o Polyhydramnios “mass effect” o Preeclampsia – hypertension, proteinuria, edema o Abrubtion o Preterm labor • Complications o Discordancy of growth – 20-25% difference in fetus size o Congenital abnormalities – 2 major ones are heart and neural tube defects o Chromosomal abnormalities (Trisomy 21) I. Problems affecting the mother 1. Pregnancy induced or aggravated hypertension 2. Maternal anemia – iron or folate deficiency, hemorrhaging (“ob is a bloody business”) 3. Maternal hemorrhage – uterine atony (over distended uterus won’t contract back down after birth, sometimes need transfusions) 4. Complicated labor – preterm, preeclampsia, fetal position 5. Hydramnios – mass effect (distended uterus, stimulus of contractions) II. Problems affecting the fetus 1. Increased incidence of spontaneous abortion 2. Perinatal mortality 3. Low birth weight – prematurity, intrauterine growth restriction 4. Malformations – fetus-in-fetu (parasitic twin), acardia (pump twin, not fully formed and takes blood from normal twin) 5. Fetal to fetal hemorrhage 6. Placental disorders – abruption (premature separation of placenta, 1% of normal population, 5-10% in twin pregnancies), Placenta Previa (placenta covers cervix) D. Misc. Info. (He said he was required to say) • Superfecundation (cats and dogs) – fertilization of 2+ oocytes in same cycle • Superfetation – ovulation during established pregnancy resulting in delayed twin