Knowledge | Started as twins in early pregnancy, but later only one remained? The medical explanation
Since the mid-20th century, doctors have observed an unusual phenomenon: some babies born as apparent singletons were originally part of a twin or multiple pregnancy. Early in pregnancy, one fetus miscarries unnoticed, and its tissue is absorbed by the mother or the surviving fetus. This is known medically as vanishing twin syndrome (VTS).
Medical imaging reveals the truth behind the “disappearance”
Before ultrasound became widely available, doctors could detect evidence of a second fetus only by examining the placenta after delivery. Today, early ultrasound can show two gestational sacs, while a later scan may show only one. This technological advance allows vanishing twins to be identified promptly.
More common than expected
Studies indicate that vanishing twin syndrome occurs in about 36% of twin pregnancies and nearly half of higher-order multiple pregnancies.
Some researchers suggest that the condition may be more common with the growing use of in vitro fertilization (IVF) and other assisted reproductive technologies. During IVF, doctors often transfer multiple embryos, but not all develop to term.
Another analysis covering nine independent studies found wide variation in reported rates of vanishing twin syndrome, related to ultrasound performance, scan timing, and data completeness. Without an early pregnancy ultrasound, doctors may never know that the pregnancy began as twins.
Main causes of a vanishing twin
In most cases, fetal chromosomal abnormalities are the main reason an embryo or fetus stops developing early. These abnormalities are usually present from fertilization rather than arising later in pregnancy.
Factors associated with increased risk include:
Maternal age over 30;
Use of IVF or other assisted reproductive technologies;
Abnormal placental development;
Intrauterine infection, such as rubella;
Genetic factors.
Effects on the mother
Most pregnant women who experience a vanishing twin have no obvious symptoms. Some may have mild abdominal pain or spotting, which are relatively common in early pregnancy.
If it occurs in the first trimester, doctors usually do not need to provide additional treatment. If it occurs in the second or third trimester, the pregnancy is classified as high risk and monitored more closely.
Overall, most of these pregnancies progress normally. However, statistics show a slightly higher likelihood of gestational diabetes, preterm birth, labor induction, or low amniotic fluid after VTS.
Potential risks to the surviving fetus
In a twin pregnancy, the risk depends on whether the fetuses share a placenta. If they do, the death of one fetus may affect the blood supply of the other. Doctors use frequent ultrasound monitoring to check the health of the surviving fetus.
Early research, including a 1997 study, suggested a possible risk of cerebral palsy in the surviving fetus, but later studies did not confirm this. Overall, the medical consensus is:
If each fetus has a separate placenta and the loss occurs early in pregnancy, there is usually little effect on the surviving fetus;
If it occurs in the second or third trimester, it may cause fetal growth restriction, low birth weight, or even a higher risk of perinatal death.
Psychological and emotional effects
A vanishing twin is not only a medical event; it may also have an emotional impact. For some parents, it represents a hidden miscarriage and may cause grief, guilt, or anxiety. Some research even suggests that surviving twins may have complex emotional reactions when they later learn they once had a twin. Doctors recommend counseling and support when needed.
Expert guidance
Although vanishing twin syndrome can sound alarming, in most cases it does not affect the pregnancy outcome. Experts recommend:
An ultrasound in early pregnancy to support early detection and clinical assessment;
Following medical guidance and attending regular prenatal visits;
Monitoring emotional well-being and seeking professional support when needed.
Knowledge | Twins in Early Pregnancy, Then Only One Remains? The Medical Explanation
Knowledge | Started as twins in early pregnancy, but later only one remained? The medical explanation
Since the mid-20th century, doctors have observed an unusual phenomenon: some babies born as apparent singletons were originally part of a twin or multiple pregnancy. Early in pregnancy, one fetus miscarries unnoticed, and its tissue is absorbed by the mother or the surviving fetus. This is known medically as vanishing twin syndrome (VTS).
Medical imaging reveals the truth behind the “disappearance”
Before ultrasound became widely available, doctors could detect evidence of a second fetus only by examining the placenta after delivery. Today, early ultrasound can show two gestational sacs, while a later scan may show only one. This technological advance allows vanishing twins to be identified promptly.
More common than expected
Studies indicate that vanishing twin syndrome occurs in about 36% of twin pregnancies and nearly half of higher-order multiple pregnancies.
Some researchers suggest that the condition may be more common with the growing use of in vitro fertilization (IVF) and other assisted reproductive technologies. During IVF, doctors often transfer multiple embryos, but not all develop to term.
Another analysis covering nine independent studies found wide variation in reported rates of vanishing twin syndrome, related to ultrasound performance, scan timing, and data completeness. Without an early pregnancy ultrasound, doctors may never know that the pregnancy began as twins.
Main causes of a vanishing twin
In most cases, fetal chromosomal abnormalities are the main reason an embryo or fetus stops developing early. These abnormalities are usually present from fertilization rather than arising later in pregnancy.
Factors associated with increased risk include:
Maternal age over 30;
Use of IVF or other assisted reproductive technologies;
Abnormal placental development;
Intrauterine infection, such as rubella;
Genetic factors.
Effects on the mother
Most pregnant women who experience a vanishing twin have no obvious symptoms. Some may have mild abdominal pain or spotting, which are relatively common in early pregnancy.
If it occurs in the first trimester, doctors usually do not need to provide additional treatment. If it occurs in the second or third trimester, the pregnancy is classified as high risk and monitored more closely.
Overall, most of these pregnancies progress normally. However, statistics show a slightly higher likelihood of gestational diabetes, preterm birth, labor induction, or low amniotic fluid after VTS.
Potential risks to the surviving fetus
In a twin pregnancy, the risk depends on whether the fetuses share a placenta. If they do, the death of one fetus may affect the blood supply of the other. Doctors use frequent ultrasound monitoring to check the health of the surviving fetus.
Early research, including a 1997 study, suggested a possible risk of cerebral palsy in the surviving fetus, but later studies did not confirm this. Overall, the medical consensus is:
If each fetus has a separate placenta and the loss occurs early in pregnancy, there is usually little effect on the surviving fetus;
If it occurs in the second or third trimester, it may cause fetal growth restriction, low birth weight, or even a higher risk of perinatal death.
Psychological and emotional effects
A vanishing twin is not only a medical event; it may also have an emotional impact. For some parents, it represents a hidden miscarriage and may cause grief, guilt, or anxiety. Some research even suggests that surviving twins may have complex emotional reactions when they later learn they once had a twin. Doctors recommend counseling and support when needed.
Expert guidance
Although vanishing twin syndrome can sound alarming, in most cases it does not affect the pregnancy outcome. Experts recommend:
An ultrasound in early pregnancy to support early detection and clinical assessment;
Following medical guidance and attending regular prenatal visits;
Monitoring emotional well-being and seeking professional support when needed.
Story source:
Collected online