The discovery of a twin pregnancy is often met with excitement, but the possibility of complications, including the loss of one fetus, can cause worry. The question of whether one twin can be lost in the earliest stages of development, such as at five weeks gestation, is a recognized medical phenomenon. This occurrence is a known part of early human development, especially in pregnancies detected through early imaging.
Understanding Vanishing Twin Syndrome
It is possible for a pregnancy that begins with two embryos to continue with only one, even when the loss occurs as early as five weeks. The medical term for this event is Vanishing Twin Syndrome (VTS). VTS describes the spontaneous demise of one embryo or fetus in a multiple gestation pregnancy, usually during the first trimester. Early ultrasound technology has made the diagnosis of VTS more common, revealing that it may affect up to 36% of twin pregnancies.
The mechanism behind the “vanishing” is resorption. The non-developing fetal tissue, including the gestational sac, is typically absorbed by the remaining twin, the placenta, or the mother’s body. Since five weeks is an extremely early stage, the tissue mass is very small, making complete and rapid absorption highly likely. This process is generally considered harmless to the pregnant person.
The cause for the demise of one twin is most often attributed to developmental issues within that specific embryo. Chromosomal abnormalities are frequently identified as a major contributing factor that prevents proper development. The loss is a natural biological process where the body recognizes and terminates a non-viable pregnancy. This occurrence is a random event and, in most cases, could not have been prevented.
Clinical Signs and Diagnostic Confirmation
For many patients, Vanishing Twin Syndrome is completely asymptomatic, meaning they experience no physical signs of the event. The loss is then discovered incidentally during a routine prenatal appointment. This is especially true when the loss occurs very early, before the body has a strong physical reaction.
If symptoms do occur, they are typically mild and non-specific, often mimicking common first-trimester discomforts. Signs may include slight vaginal bleeding or spotting, mild uterine cramping, or pelvic discomfort. Patients should recognize that these symptoms do not necessarily mean the loss of the entire pregnancy, but any bleeding or cramping warrants contacting a healthcare provider for evaluation.
Diagnosis relies on careful interpretation of ultrasound scans. An initial early ultrasound, such as one performed at five weeks, may show two separate gestational sacs or two distinct embryos. A subsequent follow-up scan, often performed a few weeks later, then reveals only one viable fetus with a detectable heartbeat. The second gestational sac may appear collapsed, empty, or completely disappeared due to reabsorption. This comparison between the initial and later imaging confirms the Vanishing Twin Syndrome diagnosis.
Prognosis for the Surviving Fetus and Subsequent Monitoring
When the loss of one twin occurs in the first trimester, particularly at five weeks gestation, the prognosis for the surviving fetus is favorable. The early timing of the loss means the surviving twin is typically not affected by the demise of the co-twin. The pregnancy is expected to progress as a standard singleton pregnancy.
Primary follow-up care involves continued routine monitoring to ensure the surviving fetus is developing normally. Healthcare providers will watch for signs that the reabsorption process is complete and that the mother is stable. The risk of complications to the survivor is minimal when the event happens before eight to ten weeks.
The surviving twin’s health remains the focus, and the pregnancy is managed without special intervention. If the loss had occurred later in the first trimester or beyond, the pregnancy might be monitored more closely for potential risks such as preterm birth or low birth weight. For a very early loss, ongoing care aligns with the standard checks and scans for any healthy singleton pregnancy.