Vanishing Twin Syndrome Diagnosis and Treatment

Introduction

Vanishing twin syndrome (VTS), as the name suggests, is a condition defined as miscarriage (the loss of an embryo from fertilisation till 8 weeks or, a foetus from 9 weeks till birth before it's developed enough to survive) that causes pregnancy involving multiple embryos to become a singleton (one) pregnancy. The syndrome gets its name from the disappearance, death, or partial or complete resorption of embryos or sets of twins, reducing a multi-foetus pregnancy to a singleton pregnancy. In this syndrome, the number of embryos visible in early pregnancy during an ultrasound exam differs from the delivered number of foetuses. This syndrome commonly occurs during the first trimester (from the first day of the last period until the end of week 12) of pregnancy. 

Understanding vanishing twin syndrome

VTS is a type of miscarriage in which the embryos in a multiple pregnancies (pregnancy involving multiple embryos) are reabsorbed either partly or completely during the first trimester by the mother, and the surviving embryo.1 VTS leads to a reduction in the number of babies anticipated during the initial phase of pregnancy. This syndrome is reported in 15 to 30% of multi-fetus pregnancies.² Most pregnant patients lose an embryo before their first ultrasound, thereby making it difficult to assess how common VTS truly is. Finding out about VTS is easier in pregnancies achieved through assisted reproductive technologies (ARTs) such as in vitro fertilisation (IVF). This is because the likelihood of getting an ultrasound in the early stages of pregnancy is higher in these cases making it easier to discover the absence of an embryo which once existed. Advancements in IVF techniques have enhanced the understanding of this syndrome because these pregnancies are closely monitored, and the number of fertilised eggs that have been implanted is known. 

Causes and risk factors

In many cases, the exact cause of VTS remains unknown. There are certain risk factors that have been associated with VTS, which include:

• Advanced maternal age of more than 30 years² 
• Use of assisted reproductive techniques such as IVF³ 
• Chromosomal abnormalities
• Multiple gestations (pregnancy with more than one baby)
• Anatomical anomalies of placenta
• Improper implantation of cord
• Genetic and teratogenic (ability to disturb the growth and development of an embryo or foetus) factors⁴ 

Signs and symptoms of vanishing twin syndrome

The most common symptoms of VTS include:

• Vaginal bleeding⁵ 
• Cramps in the uterus 
• Back pain 
• Pelvic pain 

Diagnosis of VTS

Ultrasound examination

Doctors can diagnose VTS via an ultrasound examination during the first trimester of pregnancy. The primary reason for early evaluation might be bleeding in the first trimester. The first ultrasound at 6 to 7 weeks is helpful in demonstrating twin gestation. VTS is confirmed when an ultrasound done at the end of the first trimester reveals a single foetus instead of the twin foetuses seen in the previous examination.

Human chorionic gonadotropin (hCG) test

Healthcare providers also test the levels of human chorionic gonadotropin (hCG) hormone, which is produced by the body during pregnancy, to detect VTS. An hCG level which was once high enough to support multiple gestations but stabilises later instead of continuing to rise as expected, can be an indicator of VTS. Additionally, pregnancies with VTS have a slower rate of rise in hCG as compared to twin pregnancies with normal progression.⁶ 

Management and treatment of VTS

First-trimester VTS

No special medical care is necessary for an uncomplicated VTS occurring during the first trimester of pregnancy. The mother may experience symptoms like vaginal spotting, bleeding, or pain in the pelvis, for which regular medical care is recommended. There are high chances of survival and normal delivery of the remaining foetus.⁷ 

If a foetus papyraceus (mummified foetus) remains, regular ultrasonographic evaluation of the surviving foetus should be done during the entire course of pregnancy to avoid risks like preterm labour, obstruction of labour, or death of the surviving fetus.⁸ Regular checkups are needed so that the healthcare provider can monitor the pregnant patient for infections and other complications. Physical and mental development of the viable twin is regularly monitored as well. Pregnant patients are instructed to seek immediate medical care in case of vaginal bleeding, cramping, and pelvic pain. 

The chances of survival of the viable twin are higher if the co-twin is lost during the first trimester with no adverse effect on maternal and foetal health.

Second or third-trimester VTS

Pregnancies involving VTS after the first trimester are closely monitored by healthcare professionals as they are considered high-risk. High-risk pregnancies increase the chance of premature labour or other serious health problems in the viable twin. In such cases, regular prenatal visits might help in avoiding any complications or unwanted outcomes and keep a check on foetal and maternal health ⁹. 

Complications of VTS

Mother and foetus are likely to develop complications after VTS depending upon the trimester of pregnancy.

Complications in the first trimester 

First-trimester VTS is accompanied by complications such as vaginal bleeding,¹⁰ spotting, pelvic or back pain. The mother may experience a normal pregnancy and give birth to a viable co-twin without complications. 

Complications in the second or third trimester 

Chances of complications in the mother and the viable twin are higher if VTS occurs in the second or third trimester. Maternal complications include gestational diabetes, preterm labour, or labour obstruction¹¹ and infection from a retained foetus. Complications in the surviving foetus include intrauterine growth retardation (IUGR) (poor growth of baby in the womb), preterm labour, and other congenital anomalies.⁴ VTS in the second or third trimester has also been linked to a higher chance of cerebral palsy in the viable twin.¹² 

In patients diagnosed with VTS after achieving pregnancy using IVF, obstetric complications such as premature birth or low birth weight are higher.¹³

FAQ’s

Is vanishing twin syndrome common?

This syndrome has been commonly observed in half of the pregnancies with three or more gestational sacs (fluid-filled sacs around the embryo during the first few weeks of development), 36% of twin pregnancies, and 20 to 30% of pregnancies achieved through ARTs.¹⁴

Summary

Vanishing twin syndrome (VTS) is a type of miscarriage that can occur in pregnancies involving multiple embryos, where one embryo is lost during gestation. Diagnosis typically occurs during ultrasound scans performed between 8-12 weeks of pregnancy. During early pregnancy, the count of embryos detected via ultrasound may not align with the number of foetuses eventually delivered. In some cases, one of the twins or multiple embryos may not survive, leading to its disappearance or partial/complete resorption. This results in a spontaneous reduction of a multi-fetus pregnancy to a singleton, portraying the image of a vanishing twin and confirming the diagnosis of VTS. The cause of VTS is still unknown, however, certain risk factors include maternal age over 30 and the use of Assisted Reproductive Techniques (ARTs). 

Uncomplicated VTS occurring in the first trimester does not require any special medical care. Patients may experience symptoms such as vaginal bleeding, mild abdominal cramping, pelvic pain, and abnormal hCG levels after suffering from VTS which would require regular medical care. The viable foetus has a higher chance of survival after delivery. If VTS occurs in the second and third trimester, it may cause complications such as preterm labour, obstructed labour, and infection in the case of a mummified foetus. The viable foetus may be at a higher risk of developing cerebral palsy. In some cases, early delivery may be necessary. Treatment options are limited, with regular monitoring and ultrasound scans recommended throughout pregnancy. Better healthcare outcomes in patients who have experienced VTS and their viable remaining foetus can be achieved with consistent communication, physical and diagnostic assessments, keeping track of the patient's health updates, and addressing their mental well-being.