Multiple Pregnancies Flashcards
Background for Ultrasound Scans Background: Determination of Chorionicity: Pregnancy Dating: Measurements: Dichorionic Twins: Monochorionic Diamniotic : Mono mono Twins: Trichorionic Triplets: Mono or Di Triplets:
Background: Multiple births account for 2-3% of all live births and the incidence is increasing due to assisted conception and increasing maternal age.
Perinatal mortality and morbidity is higher with multiple pregnancies than singletons and therefore these pregnancies require additional support.
The risk of pregnancy complications is much higher in monochorionic (MC) than dichorionic (DC) pregnancies.
Two-thirds of twins are dizygotic (non-identical) and one-third monozygotic (identical). One-third of monozygotic twins are dichorionic (DC) and two-thirds are monochorionic (MC). Therefore, all MC twins are monozygotic and 6 of 7 DC twins are dizygotic.
In DC pregnancies the inter-fetal membrane is composed of a central layer of chorionic tissue sandwiched between two layers of amnion, whereas in MC pregnancies there is no chorionic layer.
Determination of Chorionicity: The best way to determine chorionicity by ultrasound at 11-13 weeks’ gestation is to examine the junction between the inter-fetal membrane and the placenta. In DC pregnancies there is a triangular placental tissue projection (λ sign) into the base of the In MC pregnancies there is no placental tissue projection into the base of the membrane (T sign).
With advancing gestation, there is regression of the chorion laeve and the ‘lambda’ sign becomes progressively more difficult to identify. Thus by 20 weeks only 85% of DC pregnancies demonstrate the λ sign.
Pregnancy Dating: Spontaneous conception: use the crown-rump length of the longest fetus at 11-13 weeks.
IVF conception: use the embryonic age from fertilization.
Measurements: In each scan assess fetal growth (head circumference, abdominal circumference, femur length), amniotic fluid (deepest vertical pool), pulsatility index by Doppler (umbilical artery, middle cerebral artery and ductus venosus) and in monochorionic twins middle cerebral artery peak systolic velocity to detect possible twin anemia–polycythemia sequence (TAPS).
At 20 weeks measure cervical length. If <20 mm give vaginal progesterone 400 mg in the morning and 400 mg at night and repeat the scan in 1 week. If there is progressive cervical shortening to <5 mm give prophylactic steroids for fetal lung maturity. There is no evidence that bed rest or cervical cerclage is beneficial.
Dichorionic Twins: Scans at 12, 20 weeks and then every 4 weeks until delivery.
If there is discordance in fetal size of >15%, discordance in amniotic fluid or any abnormal Dopplers then review every 1 week.
If there is no complication, consider delivery at 37 weeks.
Monochorionic Diamniotic : Scans at 12 and 16 weeks and then every 2 weeks until delivery.
If there is discordance in fetal size of >15%, discordance in amniotic fluid or any abnormal Dopplers then review every 1 week.
If there is no complication, consider delivery at 36 weeks.
Mono mono Twins: Scans at 12 and 16 weeks and then every 2 weeks until delivery.
If there is discordance in fetal size of >15% or any abnormal Dopplers then review every 1 week.
If there is no complication, delivery by cesarean section at 32 weeks.
Trichorionic Triplets: 12 weeks: counsel concerning options of expectant management or embryo reduction.
Scans at 12, 20, 24, 28 and 32 weeks.
If there is discordance in fetal size of >15%, discordance in amniotic fluid or any abnormal Dopplers then review every 1 week.
Mono or Di Triplets: 12 weeks: counsel concerning options of expectant management or embryo reduction.
Scans at 12 and 16 weeks and then every 2 weeks until delivery.
If there is discordance in fetal size of >15%, discordance in amniotic fluid or any abnormal Dopplers then review every 1 week.
If there is no complication, delivery by cesarean section at 32-34 weeks.
MC Twins: Conjoined Twins
Prevalence: 1% of monochorionic twins.
Results from incomplete splitting of the embryonic mass after day 12 of fertilization.
Ultrasound: Fused twins in monochorionic monoamniotic pregnancy.
Classified according to the site of fusion followed by pagus (Greek word for ‘what is fixed’). Most common type is thoracopagus (75% of cases) with fusion in the thorax and abdomen and often conjoined hearts, livers and intestines.
Other types include pygopagus (fetuses fused at the rump), ischiopagus (fetuses fused at the lower half of the bodies with spines conjoined end to end at 180o angle), craniophagus (fused skulls and separate bodies), omphalopagus (fused at the lower abdomen, with shared liver and intestines).
Assoc Abnorms: The incidence of chromosomal abnormalities and genetic syndromes is not increased.
Management: Pregnancy termination, stillbirth or neonatal death in >90% of cases.
If the pregnancy continues, delivery should be by cesarean section in a centre with expertise in the management of such pregnancies.
Prognosis: Very high risk of handicap in survivors.
Recurrence: No increased risk of recurrence.
MC Twins: Death of One Fetus
Implications:
Management:
Prevalence: Spontaneous death of one fetus occurs in 1% of monochorionic twins.
Implications: Death of one twin is associated with acute hemorrhage from the co-twin into the fetoplacental unit of the dead one. In the co-twin there is a 15% risk of death and ≥ 25% of the survivors have severe neurological injury. There is also a high risk (60-70%) of preterm birth.
If death of a fetus occurs at <24 weeks’ gestation the co-twin is more likely to also die but if it survives, neurologic damage may be less; if death occurs >24 weeks the co-twin is more likely to survive but also more likely to suffer brain damage.
Management: Ultrasound examination to estimate whether the death of the fetus occurred within the previous 48 hours or earlier (mild generalized edema, ascites and pleural effusions), and assessment of the survivor for evidence of brain hemorrhage, heart failure and hyperdynamic circulation with high middle cerebral artery peak systolic velocity (MCA PSV).
Death at <48 hours and MCA PSV ≥1.5 multiple of the median: intrauterine blood transfusion and repeat Doppler 5-10 hours later. If the PSV is again >1.5 multiple of the median another transfusion is necessary. If there is polyhydramnios and the cervical length is <20 mm consider amniodrainage.
Death at <48 hours and MCA PSV <1.5 multiple of the median: repeat Doppler studies within 24 hours. If the PSV becomes >1.5 multiple of the median an intrauterine blood transfusion is necessary. If there is polyhydramnios and the cervical length is <20 mm consider amniodrainage.
Death at >48 hours and no evidence of fetal heart failure: expectant management irrespective of MCA PSV. If there is polyhydramnios and the cervical length is <20 mm consider amniodrainage.
If the fetus survives: neurosonography should be carried out in 2 and 4 weeks and MRI at 32 weeks to determine if there is evidence of brain damage. If brain development, fetal growth and Dopplers are normal there is no need for early delivery. If there is evidence of brain damage, in some countries pregnancy termination would be a legal option.
MC Twins: Monoamniotic
Prevalence: 5% of monochorionic twins.
Results from splitting of the embryonic mass after day 9 of fertilization.
Ultrasound: Absence of inter-twin membrane. The two umbilical cords insert close to each other with large-caliber anastomoses between the two fetal circulations.
Color Doppler demonstrates cord entanglement in most cases and this is usually present from the first trimester of pregnancy. Cord entanglement does not contribute to fetal death or brain damage.
The number of yolk sacs does not accurately predict amnionicity, because a few monoamniotic twins have two yolk sacs and a few diamniotic twins have only one yolk sac.
Assoc Abnorms: The incidence of chromosomal abnormalities and genetic syndromes is not increased.
Risk of discordance for structural abnormalities (20%) is higher than in monochorionic diamniotic twins (8%)
Management: Fetal death, usually of both twins, occurs in 70% of cases (50% at <20 weeks’ gestation, 15% at 20-32 weeks and 5% at ≥32 weeks).
The most likely cause of fetal death, which occurs suddenly and unpredictably, is acute exsanguination across the large anastomoses between the two cords, probably triggered by cord compression.
Discordance for major abnormality: one option is endoscopic cord occlusion of the affected fetus followed by laser transection of the cord to avoid subsequent death of the healthy twin in later pregnancy.
TTTS occurs rarely and is suspected by the development of polyhydramnios and the finding of small or absent bladder in the donor and large bladder in the recipient. The proximity of cords precludes the option of endoscopic laser ablation of communicating vessels. Alternative options are amniodrainage, early delivery or endoscopic occlusion and transection of the cord of one of the fetuses.
There is no need for hospitalization. Delivery should be by elective cesarean section at 32 weeks’ gestation.
Recurrence: No increased risk of recurrence.
MC Twins: Selective Fetal Growth Restriction
Prevalence: 10-15% of monochorionic twins.
Ultrasound: Estimated weight <5th percentile in the small fetus and ≥25% discordance between the two fetuses.
The amniotic fluid in the small fetus is reduced and in the other fetus is normal.
The condition is subdivided into 3 types according to the Doppler finding of the end diastolic flow (EDF) in the umbilical artery of the small fetus:
Type I: EDF positive.
Type II: EDF absent or reversed
Type III: EDF cyclical change from positive to absent and reversed.
If in the presence of ≥25% estimated weight discordance between the fetuses there is polyhydramnios in the sac of the bigger twin the condition is sFGR with superimposed TTTS.
Assoc Abnorms: The incidence of chromosomal abnormalities or genetic syndromes is not increased.
Management: Types I and II with TTTS: endoscopic laser ablation of communicating placental vessels.
Type I without TTTS: expectant management with close monitoring to define the best time of delivery. If Doppler finding remain normal then elective cesarean section at 34-35 weeks. There is intact survival of both twins in 95% of cases.
Type II without TTTS: there is a high risk of perinatal death and handicap for both twins.
≥26 weeks: the best management is close monitoring and delivery if the ductus venosus EDF becomes negative or reversed.
<26 weeks: the best management is endoscopic laser ablation of communicating placental vessels. Survival of the big baby is 70% and of the small baby depends of ductus venosus EDF: 40% if positive and 10% if negative or reversed. Risk of neonatal cerebral lesions primarily depends on gestational age at delivery and varies from 20% for birth at <26 weeks to 5% for birth at ≥32 weeks. An alternative management is cord occlusion of the small fetus; the survival of the large twin is 90%.
Type III: the two umbilical cords are adjacent to each other and the behaviour of the pregnancy is similar to that of monoamniotic twins; development of TTTS is rare and sudden unexpected death could occur in 20-30% of cases. Laser surgery may be impossible and the best management is close monitoring and delivery on the basis of ductus venosus EDF in the small fetus. If the ductus venosus EDF is positive elective delivery should be by cesarean section at 32 weeks’ gestation. There is a 20% risk of neonatal cerebral lesions and the risk is greater in the larger than small fetus.
Recurrence: No increased risk of recurrence.
MC Twins: Twin Anaemia-Polycythemia Sequence
Prevalence: Spontaneous: 5% of monochorionic twins. Usually occurs >26 weeks’ gestation.
After laser ablation of placental vessels: 2-10% of monochorionic twins.
Ultrasound: TAPS occurs due to a slow transfusion of blood from the donor to the recipient through few very small arteriovenous vascular anastomoses leading to highly discordant hemoglobin levels.
There is no substantial difference between the twins in either size or amniotic fluid volume.
The placenta of the anemic fetus looks thick and hyperechogenic, whereas that of the polycythemic fetus looks thin and translucent.
The fetal middle cerebral artery peak systolic velocity (MCA PSV) in the anemic fetus is increased (>1.5 multiples of median), whereas that in the polycythemic fetus is decreased (<1 multiples of the normal median).
The anemic fetus may have a dilated heart, tricuspid regurgitation and ascites. The liver of the polycythemic fetus has a starry sky pattern due to diminished echogenicity of the liver parenchyma and an increased brightness of the portal venule walls.
Assoc Abnorms: The incidence of chromosomal abnormalities, genetic syndromes or fetal defects is not increased.
Management: <26 weeks: endoscopic laser ablation of communicating placental vessels. Subsequently, scans every 1 week to monitor fetal growth, brain anatomy and MCA-PSV. Fetal brain MRI at ≥32 weeks’ gestation should be considered for the diagnosis of neuronal migration disorders. If both babies are developing normally vaginal delivery can be carried out at 37 weeks.
26-30 weeks: intrauterine blood transfusions to the anemic twin and exchange transfusion with Hartmans’ solution for the polycythemic twin. Doppler assessment every 2-3 days because it may become necessary to undertake interventions every 3-4 days. Delivery by cesarean section at 30-32 weeks.
>30 weeks: delivery by cesarean section.
Prognosis: Neurodevelopmental delay in up to 20% of cases, which mainly depends on gestational age at birth. The risk is higher for the recipient twin.
Recurrence: No increased risk of recurrence.
MC Twins: Twin Reversed Arterial Perfusion Sequence
Prevalence: 2-3% of monochorionic twins.
Ultrasound: Monochorionic twins with one normal fetus (pump twin) and another with no cardiac acitivity (rarely, a rudimentary heart may show slow pulsations) and variable degrees of deficient development of the head and upper limbs and hydrops (recipient twin).
Color Doppler in the recipient twin demonstrates reversed pulsatile flow from an umbilical arterioarterial anastomosis and venous return to the pump twin via a venovenous anastomosis. Occasionally, the cord of the acardiac twin arises directly from that of the pump twin.
The size of the acardiac mass is prognostic value for the survival of the pump twin.
About 50% of pump twins die before or after birth from congestive heart failure or severe preterm birth, due to polyhydramnios.
Assoc Abnorms: The incidence of chromosomal abnormalities, genetic syndromes or fetal defects is not increased.
Follow-Up: Intrauterine intervention: scan in 1 week to confirm that the pump twin is alive and that there is cessation of flow in the acardiac twin. Subsequently, standard follow-up.
No intrauterine intervention: scans every 2-3 weeks to monitor growth of the acardiac twin, heart function of the pump twin and amniotic fluid volume.
Prognosis: Depends on gestational age at birth.
Recurrence: No increased risk of recurrence.
MC Twins: Twin-to-Twin Transfusion Syndrome
Prevalence: 10-15% of monochorionic twins.
Ultrasound: There is imbalance in the net flow of blood across the placental vascular communications from one fetus, the donor, to the other, the recipient.
11-14 weeks: early TTTS is suspected if there is discordance in size of the amniotic fluid sacs, ≥20% discordance in fetal nuchal translucency (NT) thickness, or absent / reversed end diastolic flow (EDF) in the ductus venosus usually in the fetus with higher NT.
≥15 weeks: oligohydramnios (deepest vertical pool of ≤2 cm) in the sac of the oliguric or anuric donor fetus and polyhydramnios (≥6 cm at 15-17 weeks, ≥8 cm at 18-20 weeks and >10 cm at ≥20 weeks) in the sac of the polyuric recipient.
The condition is subdivided into 4 stages according to the Doppler finding of EDF in the umbilical artery and ductus venosus of both fetuses:
Stage 1: donor bladder visible, EDF positive in both vessels in both fetuses.
Stage 2: donor bladder not visible, EDF positive in both vessels in both fetuses.
Stage 3: EDF absent or reversed in either vessel in either fetus.
Stage 4: presence of ascites or hydrops in either fetus; usually the recipient.
Assoc Abnorms: The incidence of chromosomal abnormalities or genetic syndromes is not increased.
Management: Discordance in amniotic fluid (but not sufficient to fulfill the oligohydramnios / polyhydramnios sequence) with normal fetal Doppler:
Overall survival: 95%.
Progression to TTTS: 15%.
Ultrasound scans every 1-2 weeks to monitor evolution.
Stage 1:
Survival: overall 85%, at least one twin 90%.
Progression to stages 2 to 4: 20%.
Ultrasound scans every 1 week to monitor evolution.
Endoscopic laser ablation of communicating placental vessels if progression to stages 2-4 or increasing polyhydramnios and shortening of cervical length.
Stages 2-4:
<28 weeks: the best management is endoscopic laser ablation of communicating placental vessels; all communicating vessels should be ablated and the area between them should also be coagulated to achieve dichorionization of the placenta.
≥28 weeks: the best option is to deliver by cesarean section and the timing would depend on the Doppler findings in the umbilical artery and ductus venosus of both fetuses.
Stage 2: survival overall 75%, at least one twin 85%.
Stages 3 and 4: survival overall 60-70%, at least one twin 75-85%.
Neurodevelopmental impairment in survivors: 5-10%.
Follow-up after laser therapy: ultrasound scans and Doppler every 1 week until resolution of the signs of TTTS and normalization of Doppler findings and every 2 weeks thereafter with special attention for signs of brain damage, recurrence of TTTS and development of TAPS.
Normalization of amniotic fluid volume occurs after 1 week. Resolution of cardiac dysfunction in the receipient and of hydrops in stage 4 TTTS usually occurs after 3-4 weeks.
In about 1 in 1,000 cases there may be limb amputation due to thrombotic events or amniotic bands.
Recurrence: No increased risk of recurrence.
Structural Abnormalities prevalence
Dichorionic Twins
The prevalence of defects per fetus is the same as in singletons (2%) and therefore the risk of a defect in at least one fetus is 2 times as high (4%) as in a singleton pregnancy. In 10% of cases both fetuses are affected (concordance) and in 90% only one fetus is affected (discordance).
Structural Abnormalities
Monochorionic Twins
The prevalence of defects per fetus is 2 times higher than in singletons and therefore the risk of a defect in at least one fetus is 4 times as high (8%) as in a singleton pregnancy. In 20% of cases both fetuses are affected (concordance) and in 80% only one fetus is affected (discordance).
Management of pregnancies discordant for abnormality:
These pregnancies can be managed expectantly or by selective fetocide of the abnormal twin.
In cases where the abnormality is non-lethal but may result in serious handicap the parents need to decide whether the potential burden of a handicapped child is enough to risk the loss of the normal twin from fetocide-related complications.
In cases where the abnormality is lethal it may be best to avoid the risks associated with selective fetocide, unless the condition itself threatens the survival of the normal twin. For example, in anencephaly or trisomy 18 (with associated esophageal atresia or diaphragmatic hernia), there is >50% risk of development of polyhydramnios at 24-26 weeks’ gestation placing the normal twin at high risk of preterm birth and associated mortality and morbidity.
Selective fetocide in dichorionic twins:
Fetocide can be carried out by intracardiac injection of potassium chloride.
Fetocide at 11-14 weeks: risk of miscarriage 7% and risk of birth at <32 weeks 6%.
Fetocide at ≥16 weeks: risk of miscarriage 14% and risk of birth at <32 weeks 20%.
Fetocide at 32 weeks: this is a legal option in some countries and avoids risks of miscarriage and early preterm birth.
Selective fetocide in monochorionic twins:
Fetocide can be carried out by occlusion of the umbilical cord vessels through endoscopic laser, ultrasound-guided bipolar forceps or radiofrequency.
Fetocide at ≥16 weeks: risk of miscarriage 20% and risk of birth at <32 weeks 20%.
