TWINSWHAT DO I NEED TO KNOW Mono Chorionic (MC) Di Chorionic (DC) Mono Amniotic (MA) Di Amniotic (DA) Riverside Guidelines MAY 2012
DETERMIME CHORIONICITY/AMNIONICITY IN THE 1 ST TRIMESTER THIS CAN BE DIFFICULT TO DO IN MANY PATIENTS THE NIH RECOMMENDS THAT ALL twins Undergo NT ultrasound prior to 14 weeks whether DC/DA or MC/DA The patient does not have to undergo CPSP screening analyte draw if they do not desire genetic screening HOWEVER benefits of NT screening ultrasound alone should be emphasized such as• CHORIONICITY/AMNIONICITY will be validated• EARLY ONSET TTTS CAN BE DETECTED• STRUCTURAL DEFECTS ( cardiac/anatomical) have a greater likelihood of being detected. All of this information would impact the management of the pregnancy for the benefit of the baby.
Twin Gestations• The majority of significant fetal complications are related to Mono chorionicity• Monochorionic complications – Unequal placental sharing-IUGR – Twin twin transfusion syndrome 15% (TTTS) – Twin anemia polycythemia syndrome (TAPS) variant of TTTS without oligo – Acardiac twin (TRAP) – MonoAmniotic &/OR Conjoined
(MC) More Complications Require More Surveillance•Increased birth defects general structural & Cardiac (fetal echo)•Neurologic morbidity ~5% cerebral palsy in uncomplicated (MC)twins•Perinatal mortality (RR~ 3.5) in MC twins compared to DC twins• Stillbirth rates are significantly higher in MC 4.5% versus DC 1.3% (RR 3.6)•Neonatal death rates are also significantly higher MC 3.2% versus DC 2.1% (RR 1.5)•For these reasons, management protocols for MC twins requiremore intensive surveillance including: Doppler, fetal growth, & andamniotic fluid volume than standard of care protocols for DC twins.
DETERMIME CHORIONICITY/AMNIONICITY IN THE 1 ST TRIMESTER• Look for two separate placentas ( typically one posterior and one anterior = (DC)• If there is a “fused” single placenta Look for the "twin peak” sign = (DC)• “twin peak” sign is a triangular projection of chorionic tissue projecting between the amniotic sacs where they intersect with the placenta.
DETERMIME CHORIONICITY/AMNIONICITY IN THE 1 ST TRIMESTER• If there is no triangular projection (“V” )of tissue between the sacs and the membranes appear thin (ie usually difficult to see) and intersect the placenta @ a right angle typically• this is coined the “T sign”= MononChorionic (MC)
Determination of Chorionicity• Most accurate determination is between 8 to 14 weeks ( send for NT sono if not sure)• THERFORE DETERMIME CHORIONICITY IN THE 1 ST TRIMESTER – One “fused” placenta may be (DC) or (MC) – Two separate placentas (DC)• One fused placenta • T Sign = Monochorionic (MC) • Twin Peak Sign = Dichorionic (DC)
Determination of Amnionicty most ACCURATE < 10 WEEKS• 8 – 10 weeks EGA one yolk sac is almost (unfortunately not 100% ) diagnostic for MONOAMNIOTIC twins. If you think you have Monoamniotic twins send for NT sono and MFM consult to validate thin membrane present or not, regardless of one or two yolk sacs visualized.• THE EARLIER IN GESTATION THE MORE ACCURATE THE DIAGNOSIS.• To visualize the membrane in some MC twins will frequently require “high level” technology ultrasound machine.
Two fetuses / One yolk sac Mono AmnioticREFER TO MFM < 14 weeks
Dichorionic / Monochorionic and ZYGOSITY• Dizygotic twins 70% of all twins• 99% are DC/DA~ 15 % of DC placentas are Monozygotic• Monozygotic twins 30 % of all twins ~1/3 are DC/ DA ~2/3 are MC / DA ~ 1% are MC /MA or MC/conjoined
Chorionicity• Monozygotic – Single fertilized ova splits into two embryos with “identical” genes. Monochorionic placentas are always monozygotic twins – Approximately 15% of Dichorionic placentas are monozygotic twins if the zygote splits ≤3 days – SPLITS < 8 DAYS Diamniotic / Monochorionic – SPLITS < 13 DAYS Monoamniotic / Monochorionic – SPLITS > 13 DAYS Monoamniotic /Conjoined
MONOCHORIONIC• DUE TO INCREASED COMPLICATIONS• MFM SONOS Q 3 WEEKS STARTING @ 16 WEEKS INCREASING TO Q 1-2 WEEKS FOR SOME IN 2nd / 3rd TRIMESTER• START NST @ 32 WEEKS• LOW THRESHOLD FOR DELIVERY WITH “COMPLICATIONS” @ 32-36 WEEKS IF not sure consider CONSULTING MFM• NEW REGIONAL MFM RECOMMENDATIONS DELIVER NO LATER THAN 37 COMPLETED WEEKS IN UNCOMPLICATED MC TWINS
DICHORIONIC TWINS• SONO IN RADIOLOGY EVERY 4-6 WEEKS IF NO IUGR/DISCORDANCE• START SONOS @ 18-20 weeks ( eg 18-24-30-34)• INCREASED RISK FOR IUFD EXCEEEDS POSTNATAL RISK @ 38 WEEKS THERFORE ALL DELIVER BEFORE 38 COMPLETED WEEKS.
CARDIAC DEFECTS & TWINS•IVF Dichorionic & all Monochorionic twinsare at increased risk for cardiac defects•AIUM recommends Fetal echo @ ~ 20weeks for all Monochorionic twins and DCIVF twins.
NUTRITION• Weight gain — Women carrying multiple gestations should increase their daily dietary intake by ~ 600 kcal over that of a nonpregnant woman• The Institute of Medicine recommends the following cumulative weight gain by term for women carrying twins• BMI <18.5 kg/m2 (underweight) — Minimum 37 lbs• BMI 18.5 to 24.9 kg/m2 — weight gain 37 to 54 lbs• BMI 25.0 to 29.9 kg/m2 — weight gain 31 to 50 lbs• BMI ≥30.0 kg/m2 — weight gain 25 to 42 lbs