Congenital anomalies and selective fetocide
The management tactics for a discordant multiple pregnancy (when a developmental malformation is detected in only one fetus) rely on the severity of the pathology, gestational age at diagnosis, and, most importantly, on the type of placentation.
- In dichorionic twins, selective fetocide of the affected fetus is permitted. The standard technique involves the intracardiac injection of potassium chloride (KCl) solution. The procedure must be performed under strict ultrasound guidance.
- In monochorionic placentation, the use of potassium chloride is strictly contraindicated. This is due to the presence of inter-twin placental anastomoses: there is an extremely high risk of the toxic drug entering the circulation of the healthy fetus or causing massive hemorrhage into its vascular bed. In such cases, only umbilical cord occlusion methods of the affected fetus are used for selective fetocide. These include: injection of absolute alcohol directly into the intra-abdominal portion of the umbilical artery, cord ligation during fetoscopy, endoscopic laser coagulation, embolization of the affected fetus, and the introduction of a special thrombogenic coil under sonographic guidance.
Chromosomal pathology and risks
The probability of genetic disorders directly depends on the zygosity of the twins:
- In dizygotic twins, the frequency of pathology in each individual fetus is equal to that in a regular singleton pregnancy. However, the overall risk of involvement of at least one fetus in the pair doubles.
- In identical (monozygotic) twins, the risk is equal to that in a singleton pregnancy, but in the vast majority of cases genetic mutations affect both fetuses at once.
If trisomy is diagnosed in both fetuses, termination of pregnancy is clearly indicated. In case of discordance (when only one fetus is affected), two options are possible: selective fetocide of the affected fetus or prolongation of the pregnancy without any medical interventions.
It is important to consider that selective fetocide is associated with serious complications: miscarriage, preterm birth (PTB), and even the death of the healthy fetus are possible. Therefore, the decision to prolong pregnancy with a knowingly sick child is made solely taking into account the wishes of the pregnant woman and her family.
Conjoined (monostrosities) twins
Conjoined fetuses are classified according to the anatomical region of their fusion:
- Craniopagus — fusion by homologous parts of the skull (e.g., in the parietal or occipital region).
- Thoracopagus — fusion in the chest region, where the fetuses face each other by the anterior surfaces of the torso.
- Omphalopagus — connection in the umbilical region and the xiphoid process cartilage.
- Ischiopagus and pygopagus — connection of the lower parts of the torso, pelvis (ischial bones), lateral parts of the sacrum and coccyx.
Complex forms also occur in clinical practice. For example, an ultrasound at 12 weeks and 3 days may visualize craniothoracabdominopagi — multiple fusion involving the head, chest, and abdominal cavity (a single torso with two heads).
The prognosis for such children depends on the site and degree of connection, as well as the presence of associated malformations. For accurate diagnosis, assessment of potential survival, and the possibility of postnatal surgical separation, ultrasound (including realistic volume rendering technology — HDlive technology), echocardiography (EchoCG), and magnetic resonance imaging (MRI) are mandatory.
If pathology is diagnosed in early gestation, pregnancy termination is recommended. If future surgical separation of newborns is possible and the mother gives consent, expectant management is applied until the fetuses reach viability (e.g., up to 35–36 weeks). Delivery in such cases is performed exclusively via Cesarean section (CS).
Briefly: answers to topical questions
What are the indications for selective fetocide in multiple pregnancy?
Indications for selective fetocide (cessation of cardiac activity) in multiple pregnancy are severe developmental malformations and specific complications. The following indications are distinguished:
- Gross developmental anomalies — congenital malformations of one of the fetuses.
- Chromosomal pathology — in case of discordance, when only one fetus is affected.
- Combination of TTTS with selective fetal growth restriction — with discordance greater than 40% (up to 22 weeks).
- Stage IV TTTS — when there is no technical possibility of performing fetoscopic laser coagulation.
- Intrauterine surgical correction — fetocide of the recipient fetus to save the life of the donor fetus.
What specific complications are characteristic exclusively of monochorionic multiple pregnancies?
Complications caused by the presence of vascular anastomoses in a single placenta are exclusively characteristic of monochorionic multiple pregnancy. These specific conditions include:
- Acardiac twin (reversed arterial perfusion) — the most severe form, arising from umbilical artery-to-artery anastomoses, where the recipient fetus develops at the expense of the donor fetus.
- Twin-to-twin transfusion syndrome — a pathology triggered by the presence of arteriovenous anastomoses within the thickness of the monochorionic placenta.
In addition, with this type of placentation, there is a high risk of acute intrapartum transfusion during labor, which can lead to fatal hypovolemia of the second fetus.
To memorize the types of conjoined twins, focus on the Latin roots: cranio- (head), thoraco- (chest), omphalo- (navel), ischio- (pelvis). The suffix -pagus means fusion.
Class and exam questions
Why is it forbidden to use potassium chloride for fetocide in monochorionic twins?
Due to the presence of inter-twin placental anastomoses, there is a high risk of the drug entering the circulation of the healthy fetus or hemorrhage developing in its vascular bed.
What methods are used for selective fetocide in monochorionic placentation?
Umbilical cord occlusion methods are used: alcohol injection into the intra-abdominal portion of the umbilical artery, fetoscopic ligation, laser coagulation, embolization, or the introduction of a thrombogenic coil.
What is the management strategy when conjoined twins are detected in early gestation?
When diagnosing conjoined twins in early gestation, termination of pregnancy is indicated.
Who makes the decision to preserve the pregnancy if one of the fetuses has a chromosomal abnormality?
The decision to prolong pregnancy with a knowingly sick child is made solely taking into account the wishes of the pregnant woman and her family.
What else to study on this topic
- Placental morphology: formation of different types of placentation in monozygotic and dizygotic twins.
- Instrumental diagnostics: the value of ultrasound in pregnant women with multiples.
- Gestational pathology: classical and specific complications of multiple pregnancy.
- Obstetric tactics: basic management, prevention of anemia and preterm birth (PTB).
- Delivery: intrapartum complications in multiple births and indications for Cesarean section (CS).
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