Why Are Twins or Triplets Common in IVF Pregnancies?
Twins or triplets in IVF pregnancies are more common than in naturally conceived pregnancies, mainly because more than one embryo may sometimes be transferred into the uterus. If two or three transferred embryos successfully implant and continue developing, the pregnancy may result in twins or triplets.
However, IVF does not always result in multiple babies. Many IVF treatments lead to a healthy singleton pregnancy. The number of embryos transferred is decided by the fertility specialist after considering the patient’s age, embryo quality, previous treatment history and other medical factors.
Let us understand why multiple pregnancies may occur after IVF and why regular ultrasound monitoring is important.
Watch our video on: Do Twins Have the Same Heartbeat?
How Does Pregnancy Occur During IVF?
During in vitro fertilisation, commonly called IVF, eggs are collected from the ovaries and fertilised with sperm in a laboratory. The resulting embryos are observed for a few days so that their development can be assessed.
One or more suitable embryos may then be transferred into the uterus. After transfer, an embryo must attach to the uterine lining and continue developing for pregnancy to occur. This process is known as implantation.
Not every embryo that is transferred will necessarily implant. Sometimes one embryo implants, sometimes more than one implants and, in some IVF cycles, implantation may not occur.
Why Are Twins or Triplets in IVF Pregnancies More Common?
The main reason for twins or triplets in IVF pregnancies is the transfer and successful implantation of more than one embryo.
For example:
- If two embryos are transferred and both implant, twins may develop.
- If three embryos are transferred and all three implant, triplets may develop.
- If only one embryo implants, it results in a singleton pregnancy.
- If none of the transferred embryos implant, pregnancy does not occur during that IVF cycle.
When twins develop from two separately fertilised embryos, they are called fraternal or non-identical twins. Each baby develops from a different egg and sperm and has a separate genetic makeup.
Transferring more than one embryo does not guarantee twins or triplets. The final outcome depends on how many transferred embryos successfully implant and continue developing.
Can Twins Occur After a Single-Embryo Transfer?
Yes. Although uncommon, twins can develop even when only one embryo is transferred.
This can happen when a single fertilised embryo divides into two embryos during early development. The babies are then known as identical twins because they originate from the same fertilised egg.
Therefore, transferring one embryo significantly reduces the possibility of multiple pregnancy, but it cannot completely eliminate the rare chance of identical twins.
Does Every IVF Pregnancy Result in Twins?
No. It is a common misconception that IVF always results in twins.
Many IVF treatments result in a singleton pregnancy involving one baby. With improvements in fertility treatment and embryo selection, single-embryo transfer may be recommended for suitable patients to reduce the chance of a multiple pregnancy.
The number of embryos transferred may depend on:
- The patient’s age
- The quality and developmental stage of the embryos
- Previous IVF attempts
- The patient’s overall reproductive health
- Whether donor eggs are being used
- Whether genetic testing has been performed
- The specialist’s assessment of the likelihood of implantation
- The possible risks associated with multiple pregnancy
This decision must be made by the fertility specialist after individual medical assessment and counselling.
Why Do Fertility Specialists Try to Avoid High-Order Multiple Pregnancies?
Many women with twins or triplets have healthy pregnancies and healthy babies. However, carrying more than one baby can place additional demands on the mother’s body and may require closer medical monitoring.
Compared with a singleton pregnancy, a multiple pregnancy may have an increased possibility of:
- Premature delivery
- Low birth weight
- High blood pressure during pregnancy
- Gestational diabetes
- Anaemia
- Differences in the babies’ growth
- Increased need for hospital monitoring
- Delivery-related complications
- Complications associated with a shared placenta
The possibility of premature delivery generally increases with the number of babies. For this reason, fertility treatment aims not only to achieve pregnancy but also to support the safest possible pregnancy and birth.
How Are Twins or Triplets Detected?
Twins or triplets are usually detected through an early pregnancy ultrasound scan. The scan allows the doctor or radiologist to examine the pregnancy and determine how many gestational sacs and embryos are present.
An early pregnancy scan may help assess:
- Whether the pregnancy is located inside the uterus
- The number of gestational sacs
- The number of embryos
- Whether cardiac activity is present
- The gestational age of each baby
- The location and number of placentas
- The number of amniotic sacs
- Whether early development appears appropriate
An ultrasound is particularly important for twins or triplets in IVF pregnancies because early identification supports appropriate pregnancy monitoring and further medical planning.
Why Is It Important to Identify the Type of Twin Pregnancy?
Twin pregnancies are not all the same. Some twins have separate placentas and separate amniotic sacs, while others may share a placenta or, less commonly, an amniotic sac.
Ultrasound helps determine the chorionicity and amnionicity of the pregnancy. In simple terms, this means identifying whether the babies have separate or shared placentas and amniotic sacs.
This information is important because twins sharing a placenta may require closer monitoring. Certain complications can occur only in pregnancies where the babies share a placenta.
The first trimester is generally an important time to identify the type of twin pregnancy clearly.
Do Twins Have the Same Heart Rate?
Twin babies do not need to have exactly the same heart rate.
Each baby has an individual pattern of activity and movement. During an ultrasound examination, one baby may be resting while the other is more active. As a result, their heart rates can be different at the same moment.
For example, one twin may have a heart rate of 140 beats per minute, while the other may have a heart rate of 160 beats per minute.
Instead of expecting both heart rates to match, the radiologist assesses each baby’s heartbeat, movements, growth and overall well-being separately.
Do IVF Twin Pregnancies Need More Scans?
Twin and triplet pregnancies generally require closer monitoring than singleton pregnancies. However, the exact scan schedule depends on the type of pregnancy, whether the babies share a placenta and whether any medical concerns are present.
Ultrasound monitoring during an IVF multiple pregnancy may include:
- Early pregnancy or viability scan
- NT scan
- Anomaly or TIFFA scan
- Fetal echocardiography when advised
- Growth scans
- Cervical-length assessment when required
- Fetal Doppler studies when medically indicated
Your treating gynaecologist, fertility specialist or fetal medicine specialist will advise the appropriate scan schedule.
You can also read our pregnancy scan preparation guide to understand the timing, purpose and preparation required for different scans.
Clubfoot
Clubfoot, also known as talipes, causes one or both of the baby’s feet to turn inward or downward.
When it is an isolated condition, treatment after birth can often provide favourable results. Treatment may include gentle manipulation, plaster casts, braces and, in some cases, a minor procedure or surgery.
However, when clubfoot is detected during pregnancy, the fetal medicine specialist will usually examine the rest of the baby carefully. This is because clubfoot can occasionally occur along with abnormalities involving the spine, brain or another organ.
Clubfoot detected during an ultrasound should be properly evaluated, but its presence alone does not automatically mean that the pregnancy must be terminated.
Cleft Lip and Cleft Palate
A cleft lip is an opening or separation in the baby’s upper lip. It may occur alone or together with a cleft palate.
Many children born with a cleft lip or palate can receive treatment after birth. Depending on the condition, the child may require care from:
- Paediatric or plastic surgeons
- Feeding specialists
- Speech therapists
- Dentists or orthodontists
- Ear, nose and throat specialists
If a cleft is suspected during a pregnancy scan, a detailed assessment may be advised to check whether it is an isolated finding or is associated with another condition.
Certain Heart Abnormalities
Congenital heart abnormalities can range from mild findings that require observation to complex conditions requiring treatment after birth.
If the anomaly scan shows a possible heart abnormality, a fetal echocardiography scan may be advised. This specialised ultrasound evaluates:
- The heart chambers
- Heart valves
- Major blood vessels
- Heart rhythm
- Blood flow through the baby’s heart
Detecting a heart condition during pregnancy can help doctors plan follow-up scans, the place of delivery and newborn treatment.
Ultrasound Monitoring at Nisarga Diagnostics
At Nisarga Diagnostics, Sanjaynagar, Bengaluru, pregnancy ultrasound scans help assess the location and viability of the pregnancy, the number of babies, cardiac activity and early fetal development.
In twin or triplet pregnancies, ultrasound monitoring can also help assess each baby’s growth, movements, heartbeat, placenta, amniotic fluid and overall well-being.
The radiologist evaluates every baby separately because their heart rates, measurements and activity levels do not always have to be identical.
Frequently Asked Questions
Are twins or triplets in IVF pregnancies always caused by transferring multiple embryos?
No. Most multiple pregnancies after IVF occur when more than one transferred embryo implants. However, identical twins can rarely develop after a single-embryo transfer if one embryo divides into two.
If two embryos are transferred, will both definitely implant?
No. Both embryos may implant, only one may implant or neither may implant. Transferring two embryos does not guarantee a twin pregnancy.
Can three transferred embryos result in triplets?
Yes, it is possible if all three embryos successfully implant and continue developing. However, triplet pregnancies are less common because modern fertility care generally aims to reduce high-order multiple pregnancies.
When can twins be detected on ultrasound?
Twins can often be identified during an early pregnancy ultrasound. The exact findings depend on how far the pregnancy has progressed.
Can twins have different heart rates?
Yes. Each baby has an individual activity pattern, so their heart rates may be different during the scan. Each baby is assessed separately.
Can a single embryo produce triplets?
It is extremely rare, but an embryo may theoretically divide more than once. Most IVF triplet pregnancies are associated with the implantation of multiple embryos or a combination of multiple implantation and embryo splitting.
Does an IVF multiple pregnancy require additional care?
Twin and triplet pregnancies usually require closer antenatal and ultrasound monitoring. The required care depends on the number of babies, placental arrangement and the health of the mother and babies.
Conclusion
Twins or triplets in IVF pregnancies may occur when two or more transferred embryos successfully implant and develop. Identical twins may also rarely occur when a single transferred embryo divides into two.
However, IVF does not always result in twins or triplets. Many IVF treatments lead to healthy singleton pregnancies, particularly when a single embryo is transferred.
If an IVF pregnancy has been confirmed, follow the scan schedule recommended by your fertility specialist or gynaecologist. Early and regular ultrasound monitoring can help determine the number of babies, assess their development and support appropriate pregnancy care.
To enquire about pregnancy ultrasound scans at Nisarga Diagnostics, Sanjaynagar, Bengaluru, contact the centre for appointment assistance.
Medical disclaimer: This article is intended for general awareness and should not replace personalised advice from a fertility specialist, gynaecologist, radiologist or fetal medicine specialist.
Founder of Nisarga Diagnostics, is a renowned fetal ultrasound specialist with over 20 years of expertise. An alumnus of Government Medical Colleges in Mysore and Bangalore, he also holds a D.N.B. from the National Board of Examinations, Delhi, and certification from the Fetal Medicine Foundation, London. A former Professor and HOD, he has trained countless PG students and junior radiologists, shaping the future of fetal imaging in India.