It is possible for one twin to miscarry while the other continues to develop, even as early as 6 weeks into a pregnancy. This phenomenon, known as vanishing twin syndrome, is more commonly identified today due to advancements in early pregnancy detection. The loss of one twin in a multiple gestation can occur without affecting the health or continued development of the surviving twin.
Understanding Vanishing Twin Syndrome
This condition is formally known as vanishing twin syndrome (VTS), where one of the embryos detected in a multiple pregnancy stops developing and its tissue is partially or completely reabsorbed. The term “vanishing” refers to this reabsorption process, which can occur by the surviving twin, the placenta, or the pregnant individual’s body. This reabsorption is generally considered harmless.
Vanishing twin syndrome is not uncommon, particularly in the first trimester. Estimates suggest it occurs in approximately 20% to 36% of twin pregnancies. The increased use of early ultrasound examinations has led to more frequent diagnoses of VTS, as multiple gestational sacs can be identified before one subsequently disappears.
The underlying causes of VTS are not fully understood, but chromosomal abnormalities in the miscarrying twin are a significant factor. These genetic issues can prevent proper development, leading to reabsorption. Other factors, such as issues with placental development or improper implantation, may also play a role. Maternal age over 30 and the use of assisted reproductive technologies, like in vitro fertilization (IVF), are associated with a higher likelihood of VTS due to the increased incidence of multiple gestations.
Identifying Potential Signs
In many instances, vanishing twin syndrome occurs without any noticeable symptoms, and its discovery is often incidental during a routine ultrasound examination. An early ultrasound might initially show two gestational sacs or heartbeats, but a subsequent scan reveals only one developing fetus. Remnants of the reabsorbed twin may sometimes be visible on the ultrasound, though often they are completely absorbed.
When symptoms do manifest, they are typically mild and can include light vaginal bleeding or spotting, mild cramping, or pelvic pain. These symptoms can also be common in healthy early pregnancies, making definitive self-diagnosis difficult. A decrease in pregnancy symptoms, such as morning sickness, could also occur, but this is less common and often subtle.
Diagnosis relies on ultrasound technology, which can identify a non-developing or reabsorbed gestational sac alongside a viable one. Blood tests measuring human chorionic gonadotropin (hCG) hormone levels may provide clues, as levels that initially indicate a multiple pregnancy might plateau or decrease, suggesting the loss of one embryo.
Impact on the Remaining Pregnancy
For most cases, particularly when the loss of one twin occurs early in the first trimester, the surviving twin is unaffected and continues to develop normally. The prognosis for the remaining pregnancy is excellent.
While rare, if the twin loss occurs later in pregnancy, such as in the second or third trimester, there can be a slight increase in risks for the surviving twin. These might include a higher likelihood of lower birth weight or, in specific circumstances, other complications. However, these scenarios are exceptions and not the typical outcome for early first-trimester vanishing twin syndrome.
The reabsorption of fetal tissue from the vanishing twin is a natural process that does not typically pose a threat to the surviving twin. An early vanishing twin generally results in a healthy singleton pregnancy.
Seeking Medical Guidance
It is advisable to consult a healthcare provider if any concerns arise during pregnancy. If experiencing any vaginal bleeding, cramping, or pelvic pain, even if mild, contacting a medical professional is important for evaluation. While these symptoms can be associated with vanishing twin syndrome, they can also indicate other pregnancy conditions that require assessment.
Only a medical professional can provide an accurate diagnosis through examinations and ultrasound imaging. They can offer personalized advice and monitor the health of the ongoing pregnancy. Regular prenatal care appointments are important for monitoring the development of the fetus and addressing any questions or concerns that may arise throughout the pregnancy journey.