Rare and Unusual Complications of Twin Pregnancies

Ann Anderson Berry, MD; Megan Saathoff Contributor Information

November 7, 2012


In the United States, twin births account for 3-4% of live births. Patients who are pregnant with twins must be carefully followed due to the increased rate of complications with twinning.[1] Monozygotic twinning occurs when a single fertilized ovum splits after conception. The outcome depends on the timing of division. In the first 72 hours after fertilization, a diamniotic, dichorionic twin develops; between days 4 and 8, a diamniotic, monochorionic twin develops; approximately 8 days after fertilization, a monoamniotic, monochorionic twin develops; and after day 12, conjoined twins (shown) develop. Monozygotic twins occur in 4 in 1,000 births. Diagnosis is best done by ultrasound in the first or early second trimester.

Slide 1.

The image shows a normal twin (left) and an acardiac/acephalic twin (right).[1,2] Twin reversed arterial perfusion (TRAP) sequence occurs in 1% of monochorionic pregnancies, with an incidence of 1 in 35,000 births. It occurs when an acardiac/acephalic twin receives all of the blood supply from the normal or “pump” twin. Blood enters the acardiac twin in a reversed perfusion manner; it enters the fetus via an umbilical artery and exits via the umbilical vein. Excessive demands on the normal “pump” twin can cause cardiac failure in the normal twin, and if left untreated can cause death in 50-75% of cases. Treatment consists of fetal surgery to interrupt blood supply to the nonviable twin.

Slide 2.

Umbilical cord entanglement is one of the most common complications of monoamniotic, monochorionic twin pregnancies and is associated with a 20% fetal death rate.

Which of the following constitutes proper management of monoamniotic, monochorionic twins with known cord entanglement?
A. Cesarean section at 28 weeks gestation
B. Cesarean section at 32 weeks gestation
C. Cesarean section at 36 weeks gestation
D. Cesarean section at term

Slide 3.

Answer: B. Cesarean section at 32 weeks gestation

Cord entanglements can begin loosely in the first trimester, with potential to tighten and cause fetal injury or death. Abnormalities that suggest cord compression include high blood velocity in the umbilical vein, a notch in the umbilical artery waveform, or persistent absent end diastolic flow. With high risk of perinatal mortality in the third trimester, cesarean section (shown) is suggested to be done at 32 weeks gestation with an empiric course of betamethasone prior to delivery. For pregnancies continuing beyond 32 weeks, there is a 10% perinatal mortality, compared with 1-2% of those delivered at 32 weeks. Image courtesy of Wikimedia Commons.

Slide 4.

In twin-twin growth disparity, what percentage discordance between the twins is needed to meet the definition of growth discordance?
A. 5-10%
B. 10-20%
C. 20-30%
D. 30-40%
E. 50% or more

Image courtesy of Wikimedia Commons.

Slide 5.

Answer: C. 20-30%

As weight differences between the twins increase, perinatal mortality rate proportionately increases. Restricted growth of one of the twins usually occurs late in the second trimester or early in the third trimester and is usually attributed to placental vascular anastomoses. The mainstay of management is performing sonographic monitoring every 2-3 weeks starting in the second trimester. In the third trimester, middle cerebral artery peak systolic velocity is also monitored. Early delivery is usually not performed due to the sole factor of growth discordancy, except in some cases of advanced gestational ages. Image courtesy of Wikipedia Commons.

Slide 6.

Conjoined twinning (shown) refers to incomplete splitting of monozygotic twins after 12 days of embryogenesis. Conjoined twins account for 1% of monozygotic twins. In the United States, the incidence is 1 per 33,000-165,000 overall births and 1 per 200,000 live births. The stillbirth rate is 40-60%. The female-to-male ratio of conjoined twins is 3:1.[3]

What is the most common point of attachment?
A. Craniopagus (joined at the head)
B. Thoraco-omphalopagus (joined at the chest, abdomen, or both)
C. Omphalopagus (joined at the abdomen)
D. Pygopagus (joined at the buttocks)
E. Ischiopagus (joined at the ischium)

Slide 7.

Answer: B. Thoraco-omphalopagus (joined at the chest, abdomen, or both)

Conjoined twins are characterized based on their site of union (chest, head, abdomen, etc.) and the suffix –pagus, which means “fixed.” The frequency by site of attachment is 74% for thoraco-omphalopagus (i.e., joined at the chest, abdomen, or both), 40% for thoracopagus or xiphopagus (chest), 34% for omphalopagus (abdomen), 18% for pygopagus (buttocks), 6% for ischiopagus (ischium), and 2% for craniopagus (head). Xiphopagus twins are shown.[3] Image courtesy of G. Dorairajan.[4]

Slide 8.

With conjoined twins, findings that appear on prenatal ultrasound include monoamnionicity, contiguous skin, twins that stay in the same orientation to one another, fetal scoliosis, unusual limb positioning, and more than three vessels in the cord. The most common site of attachment is thoraco-omphalopagus with fusion from the anterior thorax to the umbilicus (shown). Subtypes of thoracoomphalopagus twinning include thoracopagus and omphalopagus. A common pericardial sac is present in 90% of thoracopagus twins, and conjoined hearts are seen in 75%. In omphalopagus, the anterior abdomens are united, occurring in 34% of thoracoomphalopagus twinning.

Slide 9.

Ischiopagus twins occur in 6% of conjoined twinning. These twins are characterized by fusion of the ischial spines (shown). Twins may have 3 legs (tripus) or 4 legs (tetrapus) and sometime only one head. The genitourinary system and the rectum are shared, and the liver is frequently fused.[3] Image courtesy of Y.A. Khan.[5]

Slide 10.

Craniopagus (shown) occurs in only 2% of all conjoined twins and is characterized by cranial fusion. Stone and Goodrich subclassified craniopagus into 4 varieties. Total forms share significant dural venous sinuses, whereas partial forms lack significant shared dural venous sinus systems. This classification consists of partial angular (PA), partial vertical (PV), total angular (TA), and total vertical (TV).[3,6] Image courtesy of the National Library of Medicine.

Slide 11.

Vanishing twin syndrome—the identification of a multifetal gestation with subsequent disappearance of one or more fetuses—occurs in 21-30% of multifetal gestations. There may be complete reabsorption of the fetus; formation of a fetus papyraceus or “mummified” fetus (shown); or an abnormality on the placenta including a cyst, subchorionic fibrin, or amorphous material. It is thought to result from chromosomal abnormalities or improper cord implantation. It is diagnosed by ultrasound.[7] What is the most common hypothesized pathological clinical sequela of the viable twin in vanishing twin syndrome?
A. Mental retardation
B. Congenital heart defects
C. Spina bifida
D. Cerebral palsy

Image courtesy of Wikimedia Commons.

Slide 12.

Answer: D. Cerebral palsy

Researchers hypothesize that vanishing twin syndrome results in spastic cerebral palsy in the remaining twin. Possible mechanisms include (1) transfusion of thromboplastic proteins from the vanishing twin to the surviving twin, leading to disseminated intravascular coagulation and causing intrauterine central nervous system damage or (2) large amounts of blood loss from the surviving twin to the low resistance system of the vanishing twin through placental anastomoses, causing central nervous system damage. Other complications include cutis aplasia (shown), prematurity, lower birth weight, microcephaly, isolated hydrocephaly, and cardiac anomalies.[7]

Slide 13.

An external parasitic twin (shown) occurs when a grossly defective fetus or fetal parts are attached externally to a normal twin. A parasitic twin usually consists of externally attached supernumerary limbs. A functional heart and brain are classically absent. It is believed to result from demise of the defective twin, with its surviving tissue attached to and vascularized by the normal twin.[8]

Slide 14.

Twin pregnancy consisting of a hydatidiform mole and a normal coexisting fetus is rare, with an incidence of 1 in 22,000 to 100,000 pregnancies.[9] This ultrasound image shows a normal fetus (red arrow) with an adjacent mole (yellow arrow).

What is an associated complication of this pregnancy?
A. Gestational hypertension
B. Persistent trophoblastic disease
C. Placenta accreta
D. Polyhydramnios

Slide 15.

Answer: B. Persistent trophoblastic disease

Twin pregnancy consisting of a hydatidiform mole and a normal coexisting fetus is associated with several complications, including fetal demise, vaginal bleeding, preeclampsia, and increased risk of persistent trophoblastic disease. Due to higher risk of developing persistent disease and metastasis, pregnancy termination is usually recommended. However, cases of healthy infants have been reported. Inform patients of the severe risk of maternal morbidity from complications. To evaluate the karyotype of the fetus, prenatal genetic diagnosis by chorionic villus sampling is recommended. A hematoxylin and eosin stain of a complete mole is shown.[9,10]

Slide 16.

A 25-year-old G1P0 white female at 12 weeks gestation presents to the ED with abdominal pain and cramping. She has had no pregnancy complications. Patient’s vitals include temperature of 37.5°C (99.5°F), blood pressure of 120/85 mmHg, pulse of 80 beats/minute, and respiratory rate of 18 breaths/minute. Ultrasound shows a uterine pregnancy in conjunction with an extrauterine pregnancy (arrow). What should treatment include?
A. Symptomatic management until after delivery
B. Methotrexate therapy
C. Emergency laparotomy with salpingectomy and removal of adnexal mass
D. Local injection of potassium chloride or hyperosmolar glucose into the tubal pregnancy sac under sonographic guidance

Slide 17.

Answer: D. Local injection of potassium chloride or hyperosmolar glucose into the tubal pregnancy sac under sonographic guidance

Heterotopic pregnancy is a uterine pregnancy in conjunction with an extrauterine pregnancy. Methotrexate is contraindicated due to the normal pregnancy. Salpingectomy is the first treatment line in patients with hemodynamic instability or signs of tubal rupture. Laparoscopic image (shown) illustrates an extrauterine pregnancy (E). Laparoscopy is preferable if patients are hemodynamically stable. If the pregnancy has not ruptured, local injection of potassium chloride or hyperosmolar glucose into the tubal pregnancy sac under sonographic guidance is effective.[11]

Slide 18.

Contributor Information


Ann Anderson Berry, MD
Associate Professor
Department of Pediatrics
University of Nebraska Medical Center
Omaha, Nebraska

Disclosure: Ann Anderson Berry, MD, has disclosed no relevant financial relationships.

Megan Saathoff
Medical Student
University of Nebraska Medical Center
Omaha, Nebraska

Disclosure: Megan Saathoff has disclosed no relevant financial relationships.


Lars Grimm, MD, MHS
House Staff
Department of Diagnostic Radiology
Duke University Medical Center
Durham, North Carolina

Disclosure: Lars Grimm, MD, MHS, has disclosed no relevant financial relationships.


Michel E. Rivlin, MD
Department of Obstetrics and Gynecology
University of Mississippi School of Medicine
Jackson, Mississippi

Disclosure: Michel E. Rivlin, MD, has disclosed no relevant financial relationships.


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