During in vitro fertilization (IVF), you can transfer one embryo (single embryo transfer, or SET) or two embryos (double embryo transfer, or DET). If you are a good candidate for single embryo transfer, your chance of having a baby after two single embryo transfers is as good as your chance of having a baby after one double embryo transfer. That’s important to know because twin pregnancies are risky for baby and mother.

The chart below compares the percentage of women who had single babies or twins after single and double embryo transfers among good candidates for single embryo transfer. These women were good candidates for single embryo transfer because they were using IVF for the first time and were (1) younger than 38, transferring fresh embryos created from their own eggs, and freezing at least one embryo or (2) any age and transferring fresh embryos created from donor eggs.

• 1 SET (fresh): transfer of one fresh embryo for the first IVF cycle.
• 1 SET (fresh) + 1 SET (frozen): transfer of one fresh embryo for the first IVF cycle, followed by transfer of one frozen embryo, if the first fresh embryo transfer does not lead to having a baby.
• 1 DET (fresh): transfer of two fresh embryos for the first IVF cycle.

Source: Centers for Disease Control and Prevention, National Assisted Reproductive Technology Surveillance System (NASS), 2010-2012.

Forwomen who are good candidates for single embryo transfer, transferring one fresh embryo followed by one frozen embryo, if a second transfer is needed, offers the best chance of having a baby without increasing the chance for twins.

We know that you are ready to start or add to your family. You may be concerned about your chances of having a baby using in vitro fertilization (IVF) or how much cycles of IVF cost. These concerns are common and may lead you to think about transferring more than one embryo during your IVF procedure. However, transferring more than one embryo increases your chances of having twins or more. Twin pregnancy is risky for baby and mother, whether or not IVF is used. Some of these risks include:

Almost 3 out of 5 twin babies are born preterm, or at less than 37 weeks of pregnancy. Twin babies are nearly 6 times as likely to be born preterm as single babies.

Twin babies are more likely to be stillborn, experience neonatal death, have birth defects of the brain, heart, face, limbs, muscles, or digestive system, and have autism than single babies.

About 1 out of 4 twin babies are admitted to the neonatal intensive care unit (NICU). Twin babies are more than 5 times as likely to be admitted to the NICU as single babies.

About 7 out of 1,000 twin babies have cerebral palsy. Twin babies are more than 4 times as likely to have cerebral palsy as single babies.

Twin babies are more likely to be stillborn, experience neonatal death, have birth defects of the brain, heart, face, limbs, muscles, or digestive system, and have autism than single babies.

Almost 1 out of 10 women carrying twins gets pregnancy-related high blood pressure. Women carrying twins are twice as likely to get pregnancy-related high blood pressure as women carrying single babies.

Almost 1 out of 20 women carrying twins gets gestational diabetes. Women carrying twins are 1.5 times as likely to get gestational diabetes as women carrying single babies.

Research shows that, for some women, transferring one fresh embryo followed by one frozen embryo, if a second transfer is needed, offers the best chance of having a baby without increasing the chance for twins.

The Centers for Disease Control and Prevention (CDC) tracks success rates for women who receive IVF. For the years 2010 to 2012, CDC found that transferring one embryo at a time can lead to a better chance of having at least one baby while reducing the chance of having twins. These success rates are only for patients who tried IVF for the first time using fresh (not frozen and thawed) embryos, and who were either

• Younger than 38, using embryos created from their own eggs, and with more than one embryo available for transfer.
• Any age, using embryos created from donor eggs.

The rates below are shown by day of embryo transfer, which can affect success.

• When a fresh embryo was transferred 2-3 days after retrieval, 38% of women had at least one baby, and less than 1% had twins.
• When a fresh embryo was transferred 5-6 days after retrieval, 51% of women had at least one baby, and less than 1% had twins.

During your fresh cycle, your doctor can freeze extra embryos for you to use later. If you don’t get pregnant or have a baby during your fresh cycle, you can do a frozen cycle. In a frozen cycle, the frozen embryos are thawed and transferred.

• When a fresh embryo was transferred 2-3 days after retrieval, and then a frozen and thawed embryo was transferred later if needed, 55% of women had at least one baby, and less than 1% had twins.
• When a fresh embryo was transferred 5-6 days after retrieval, and then a frozen and thawed embryo was transferred later if needed, 66% of women had at least one baby, and less than 1% had twins.

• When two embryos were transferred 2-3 days after retrieval, 49% of women had at least one baby, and 16% had twins.
• When two embryos were transferred 5-6 days after retrieval, 60% of women had at least one baby, and 27% had twins.

The option to transfer one fresh embryo followed by one thawed embryo, if needed, offers the highest chance for some IVF patients to have a baby without increasing the chance for twins. Talk with your doctor about which embryo transfer option is right for you.