IVF Twin Pregnancy Week by Week: What Mothers Need to Know

When you find out that you are having twins through IVF, it may feel like a dream came true. However, since you will have two babies in your tummy, you may wonder how they will grow week by week and whether there are any differences from carrying one baby (singleton).

To help you prepare, let's walk through each pregnancy stage, what symptoms you feel, what scans you might need, and what the main risks to be aware of.

What causes IVF twin pregnancies?

During in vitro fertilisation (IVF), twin pregnancies can occur through two main processes, known as dizygotic and monozygotic. They differ based on whether one or multiple embryos are transferred to the womb and how they develop.

Dizygotic twins

Also known as fraternal twins, dizygotic twins are the most common type of IVF twins. They occur when multiple embryos are transferred to the womb and more than one successfully implants. These multiple embryos are introduced to the womb through the double embryo transfer (DET) procedure, which increases the likelihood that at least one will implant, but it also raises the chance of twins.

Because twin pregnancies carry a higher risk for both mother and babies, doctors usually reserve DET for specific cases, such as older patients or those who have experienced repeated failed cycles. To improve safety, doctors may prefer elective single embryo transfer (eSET), which reduces the risk of twins.

Monozygotic twins

Another way for a twin pregnancy to happen during IVF is through monozygotic twins, which occur when a single transferred embryo splits into two in the early stages of pregnancy. While this splitting happens inside the womb, certain laboratory steps during IVF can increase the likelihood of it occurring.

One of the most significant factors is laboratory culture, particularly when the embryo is grown to the blastocyst stage (days 5-6) before transfer. During this time, the blastocyst expands and begins to hatch from its protective shell, this process may make the inner cells more likely to divide.

Additionally, other IVF procedures such as assisted hatching, which involves creating a tiny hole in the embryo's shell to aid implantation, may slightly increase the risk of monozygotic twins.

IVF twins pregnancy week by week

If you are expecting twins, it is only natural to want to know how your babies will grow and develop throughout your pregnancy. Seeing their progress week by week can help you to feel more prepared and make it easier to keep track of their growth.

First trimester

During the first few weeks of a twin pregnancy, there are often no signs at all. The progesterone supplements you are taking can also make it difficult to recognise the symptoms.

Common symptoms, like morning sickness, usually start around week 5 or 6 and can be more intense. However, it usually may get better after it peaks around week 9 or 10. 

Here’s what Mum can expect during this period:

• Weeks 1 to 4:

  • During weeks 1 to 4, your twins implant into the lining of your womb, and the placenta begins to form to support their growth. 

• Weeks 5 to 8:

  • Between weeks 5 and 8, both babies undergo rapid development. 
  • The brain and spinal cord begin to form, arms and legs start to take shape, and their major organs begin to develop. Their heartbeats also become detectable during this window.

• Weeks 9 to 13:

  • During this period, your babies’ features become more defined. Their fingers, toes and nails will start to appear. Their facial features, including their eyes, ears and nose, also begin to take shape. Tooth buds also form beneath the gums at this stage.

Second trimester

During this trimester, nausea often eases, and you may feel more energetic. Therefore, this period can feel more comfortable than the first trimester. 

However, in an IVF twin pregnancy, your body may also start to feel the effects of carrying two babies. Backache, shortness of breath, and round ligament pain may appear sooner and become more noticeable as the pregnancy progresses. 

• Weeks 14 to 20:

  • From weeks 14 to 20, your twins are starting to move, and you can begin to feel the first signs of movement. They become more active, with some limb movements, and their eyes start to move.
  • Soft cartilage begins to harden, hair growth becomes more visible, and your babies can now hear sounds from outside the womb. A protective coating called vernix also forms over their skin to shield them from the amniotic fluid (a fluid that surrounds and protects your babies).

• Weeks 21 to 27:

  • During weeks 21 to 27, development becomes increasingly defined. Each of your little ones starts having their unique fingerprints, their responses to sound grow stronger, and their lungs continue developing.

Third trimester 

As your babies continue to grow in the third trimester, there is very little space left in your womb. So you may experience symptoms such as rib pressure, swelling, and poor sleep. Many also have to reduce or stop working because even normal movements become very difficult.

• Weeks 28 to 36:

  • By weeks 28 to 36, your babies can open and close their eyes, and their brains are growing rapidly. Most major organ development is now complete, and their lungs are maturing in preparation for birth.

• Weeks 37 and beyond:

  • At 37 weeks and beyond, the moment you have been waiting for is finally here. Your babies are considered fully grown and ready for birth. Most women give birth after 37 to 42 weeks of pregnancy, but twin births tend to happen earlier, at around 36 to 38 weeks.

Symptoms of a twin pregnancy

When a twin pregnancy happens, you may have more symptoms compared to a singleton pregnancy, such as:

• Increased nausea

• More fatigue

• Heartburn or reflux

• Rapid weight gain

• A belly that grows faster and looks larger earlier

• Frequent urination

Additionally, twin pregnancy symptoms can be more intense and stronger than singleton pregnancies because several pregnancy hormone and protein levels are changing, such as the following:

• Higher human chorionic gonadotropin or hCG levels, produced by the placenta after implantation, often lead to severe morning sickness.

• Higher alpha-fetoprotein (AFP),a protein made by the foetus' liver, which naturally doubles when you are carrying twins.

Monitoring and prenatal care for IVF twins

If you are pregnant with twins, you will need more monitoring and prenatal care due to a higher risk of complications compared to a singleton pregnancy. These are several types of monitoring and prenatal care available for you.

First trimester

• Early chorionicity determination:

  • This scan checks for chorionicity (whether twins share a placenta) and amnionicity (if each baby has its own amniotic sac, the fluid-filled membrane that protects them). 
  • It can identify dichorionic diamniotic (DCDA) twins, with separate placentas and sacs, or monochorionic diamniotic (MCDA) twins, who share a placenta but have individual sacs. 

• NIPT (non-invasive prenatal test):

  • You can have NIPT in around 10 weeks of pregnancy. It screens your babies' DNA for chromosomal conditions and sex chromosome abnormalities.

• Nuchal translucency:

  • Nuchal translucency usually will be checked in around 11 to 14 weeks of pregnancy. 
  • It measures the fluid at the back of each baby's neck to screen for chromosomal conditions such as Down syndrome, Edwards syndrome, and Patau syndrome, as well as potential heart abnormalities.

Second trimester

• Anomaly scan:

  • You can have an anomaly scan at around 18 to 22 weeks. This scan will check your babies' organs, limbs, and any structural problems.

• Cervical length measurement:

  • Cervical length usually will be checked in around 18 to 24 weeks. It measures the lower part of the womb that opens during labour to assess your risk of preterm birth.

• Serial growth scans:

  • You can have serial growth scans from 20 weeks of pregnancy. It estimates each baby's foetal weight and tracks whether they are growing at a similar rate.
  • These scans can be carried on through the third trimester, typically every two to four weeks, to monitor foetal weight, amniotic fluid, and blood flow.

Third trimester

• Regular ultrasound scan follow-up:

  • In your third trimester, you will need regular ultrasound follow-ups to check each baby’s growth, amniotic fluid, and blood flow, usually every 2 to 4 weeks.

If you are unsure which tests are necessary for your pregnancy, schedule an appointment at Thomson Fertility Singapore. Our specialist can help decide which tests are suitable for you as well as do monitoring for early complications and risks.

IVF twin pregnancy risks and considerations

Having twins can be exciting, but it carries higher risks for mothers and babies than singleton pregnancies. These risks include: 

Preterm labour

Preterm labour is delivery before 37 weeks of pregnancy. It is one of the most common complications in twin pregnancies. In Singapore, around 60% of twins were born preterm, before 37 completed weeks of pregnancy.

Babies born early often need care in a neonatal intensive care unit (NICU), which helps with breathing, feeding, and keeping their body temperature stable. 

Gestational diabetes

Mothers expecting twins have a higher risk of gestational diabetes compared to those with singleton pregnancies. This increased risk is mostly due to a larger placenta, which raises hormone levels that stop the body from using insulin well.

Gestational hypertension 

Gestational hypertension is high blood pressure that can occur after the 20th week of pregnancy.

This condition is more common in twin pregnancies because of the increased physical demands of carrying two babies. It puts more pressure on the heart and blood vessels, raising the chance of high blood pressure.

Pre-eclampsia

Pre-eclampsia is a serious pregnancy complication characterised by high blood pressure and organ impairment, typically affecting the kidneys or liver. 

Women expecting twins face a higher risk of pre-eclampsia because of the larger placenta, which produces more anti-angiogenic proteins (a substance that blocks the body from creating new blood vessels) that can harm blood vessels and elevate blood pressure. 

Postpartum haemorrhage

Postpartum haemorrhage is a serious complication involving excessive bleeding after childbirth, often due to the womb not tightening enough after the baby is born. The risk is greater in twin pregnancies because the stretched womb struggles to tighten and seal blood vessels effectively after delivery. 

Low birth weight

Low birth weight means a baby is born weighing under 2.5 kg. Twins are at a higher risk because they are often born prematurely, which limits their growth time in the womb. Even at full term, they share space and compete for nutrients, which restricts their growth compared to singletons.

Serious pregnancy complication symptoms

While some discomfort is normal in your IVF twin pregnancy, there are certain symptoms that are considered serious pregnancy complications. If you experience any of the following, it is a sign for you to contact your doctor as soon as possible.

• Persistent or regular contraction 

• Vaginal bleeding 

• Sudden leakage of fluid

• Change in foetal movement

• Severe pain in the upper abdomen 

• Severe headache or vision changes

If you notice symptoms that may be a sign of serious pregnancy complications, it is recommended to seek medical attention as soon as possible. Schedule an appointment with our specialist at Thomson Fertility Singapore, who can assess your symptoms, check on both babies, and provide tailored advice on the next steps for your care.

Tips for a healthy twin pregnancy

Carrying IVF twins can require more challenges and efforts since you might have higher risks and symptoms than having one baby. But with the right care and support, you can go on to have healthy pregnancies and deliveries. 

Here are some practical steps you can take to look after yourself and your babies throughout the journey:

• Consume a balanced diet rich in protein and iron, as these nutrients are essential for foetal development and to prevent anaemia.

• Stay hydrated, as drinking enough water is essential to produce amniotic fluid and to increase blood volume.

• Get enough rest, as carrying twins can easily tire you. 

• Take supplements such as prenatal vitamins, iron, and folate to make sure your babies have enough nutrients.

• Regularly practise light activities such as walking and prenatal yoga to help ease back pain, improve circulation, and lift your mood.

• Manage stress by practising relaxation techniques like deep breathing or meditation, and do not hesitate to lean on friends, family, or support groups.

• Attending all your scheduled antenatal checkups to ensure both you and your babies remain safe and healthy. 

FAQ

Do twins develop differently week by week?

Twins may grow at slightly different paces from one another in weight, size, and features. A modest difference between them is common and usually nothing to worry about.

How often will I need scans?

Can twins be delivered naturally after IVF?

Yes. Being conceived through IVF treatment does not, on its own, mean you will need a caesarean section. Vaginal delivery is often possible when the first twin is head-down, both babies are growing well, and there are no other complications.

What is the ideal delivery time for twins?

Most twin pregnancies are delivered between 36 and 38 weeks of pregnancy rather than waiting until 40 weeks as with singleton pregnancies. This is because delivering during this timeframe helps to protect both your health and your babies, as carrying twins beyond 38 weeks can increase the risk of complications.

The information provided is intended for general guidance only and should not be considered medical advice. For personalised advice based on your unique conditions, request a consultation with Thomson Medical today.

References

Dhevi, L. V., Li, S. W. L., Su, L. L., Gosavi, A., & Biswas, A. (2023). A case series of higher-order multifetal pregnancies managed at a tertiary maternity unit. Annals of the Academy of Medicine, Singapore, 52(9), 484–487. https://doi.org/10.47102/annals-acadmedsg.202345

World Health Organization. (n.d.). Low birth weight. World Health Organization (WHO). Retrieved September 4, 2026, from https://www.who.int/data/nutrition/nlis/info/low-birth-weight