Vanishing twin syndrome: An unlikely maturation!


A vanishing twin syndrome-as the name suggests- is a pregnancy-related complication. It refers to a miscarriage of a twin in case of multiple pregnancies. 21-30% of multiple pregnancies can result in vanishing twin syndrome.
The condition arises in the early weeks of pregnancy rather than developing suddenly.

The primary reason is the maturation of a fetus to an embryo that was never meant to be viable. Chromosomal abnormalities and improper umbilical cord implantation are other causes of the syndrome.

Risk factors associated with vanishing twin syndrome

The chance of occurrence of this complication is during the early stages of gestation. Twin pregnancies between 5-8 weeks are susceptible to this condition. Besides, the mother’s lifestyle plays a vital role in affecting the susceptibility to the condition. Research indicates increased sensitivity in mothers over 30 years of age.

Avoiding alcohol and tobacco consumption during pregnancy can reduce the risk. However, the risk factors associated with this condition are evident during the first trimester of pregnancy. The risk decreases in the second trimester, and after 20 weeks, the chances reduce to 3%. 

The symptoms include vaginal bleeding, pelvic pain, and cramping. These symptoms are a sign of miscarriage, but none of them confirm the loss of a baby. Doctors may need to perform a D&C procedure in case of abnormal uterine bleeding.

Diagnosis

Pregnant mothers usually have many follow up scans to find out the health of the baby. A rapidly expanding uterus and high hormone levels suggest multiple pregnancies. A confirmed twin pregnancy requires close monitoring since the condition involves a unique set of complications. Doctors suspect the disease when they start hearing one heartbeat instead of two during the regular checkup. 

However, it was impossible to notice the condition with previously used diagnostic scans. The older equipment was not capable enough to confirm if the mother will have a single child or twins, within 10-12 weeks of gestation. The lost pregnancy usually goes off unnoticed. Although an ultrasound indicates singlet condition and special testing rules out triploid stage, the possibility of a vanished twin should not be ruled out.

The twin doesn’t disappear technically

In the event of a miscarriage during pregnancy, the twin doesn’t disappear technically.

The survival twin or the mother reabsorbs the fetal tissue of the vanishing twin.  Cysts on the placenta serve as traces of a lost twin.

The twin’s tissue flattens due to the pressure by the survival twin. Compression of the fetus (fetus compressus) and loss of fluid and most of the small tissue can identify the condition during delivery of the healthy child. Doctors can also diagnose a condition called fetus papyraceous during labor, which arises as a result of a lost pregnancy. The twin can sometimes be visible as a blighted ovum besides the healthy twin in an ultrasonography scan.

The risk associated with the survival twin

The quality and development of twins are related. If there is one loss, there is a possibility of a defect in the survival twin as well. The most commonly observed defect is a congenital malformation.

  • Cerebral palsy: It affects the movements and muscles of the surviving twin. The primary cause is abnormal brain development before birth.
  • IUGR: Intrauterine growth restriction is a condition in which the baby is smaller in size, unlike a typical new-born. This condition often results in abnormalities like low birth weight and rarely, Diabetes. This reduced nutrition can sometimes result in the stillbirth of the baby.

How long the DNA of the vanished twin stays in the system?

Non-invasive prenatal screening (NIPS) uses the circulating free DNA (cfDNA) to diagnose genetic abnormalities in the fetus. The risk of aneuploidy in the fetus increases with the age of the mother. Although a fetal fraction can identify a singleton pregnancy, it cannot diagnose a vanishing twin condition. The cfDNA of the twin can remain in the maternal circulation. The time depends on the autolysis of placental tissue. The age of the fetus at the time of death also serves as a factor.

After an abortion, the cfDNA of the fetus remains five times higher during the recognition of spontaneous abortion than in women with ongoing pregnancy of the same gestational age. Further, a chromosomal abnormality in the child increases the concentration of cfDNA, unlike an abortion of a healthy child with typical karyotype. 

Similarly, the DNA of a vanished twin can remain in the maternal circulation. Research suggests it can stay upto eight weeks soon after death. Additionally, this cfDNA can interfere with the results of the viable twin. There soon arises confusion in determining the sex of the fetus, since clinicians can unknowingly test the cfDNA of the vanished twin rather than the healthy one. Hence, the identification of a lost twin is critical to avoid incorrect results.

Chromosomal abnormalities associated with vanishing twin syndrome

Vanishing twins commonly generate false-positive results for chromosomal abnormalities, when total DNA is tested without detecting any other possible haplotypes. Similar conditions can result in spontaneous reductions and interfere with aneuploidy (Chromosomal abnormality) diagnosis.

Trisomy 21 (Down syndrome) and trisomy 13 (Patau syndrome) are diagnosed with low pregnancy-associated plasma protein-A (PAPP-A) and high β-human chorionic gonadotropin (β-hCG).

The level of PAPP-A consistently remained high in both spontaneous and non-spontaneous reductions. In contrast, the levels of β-hCG are high within the first four weeks.

The high β-hCG level is a favorable diagnosis of Down syndrome. However, high PAPP-A gives negative results.

Elevation of PAPP-A decreases the risk of developing trisomy disorders. In such exceptional cases, additional testing is always recommended to avoid incorrect results.

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