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Causes of Multiple Pregnancy: What You Should Know

Medically reviewed by Jobelle Ann Dela Cruz Bigalbal, MD · General Practitioner

Written by Elaine Felicitas · Updated Jun 10, 2021

Causes of Multiple Pregnancy: What You Should Know

Getting pregnant is an exciting experience for moms and moms-to-be. It can get more exciting with two or more babies on the way, at the same time. Know more about the causes of multiple pregnancy and what are the risks and complications that come with it.

Types of Multiple Pregnancies

Multiple pregnancies are defined as when a mother conceives two or more babies in one pregnancy.

There are 3 types of multiple pregnancies are:

Fraternal or dizygotic twins are the common type of multiple pregnancies among the 3. Dizygotic means two cells where the baby is conceived with two separate eggs and sperm. The twins might not look similar to each other and may have of different sex as they are born out of different cells.

Identical or monozygotic twins happen when a fertilized egg divides into two. As they are from one egg or monozygotic, their features are identical including their sex. They grow to be more like mirror images of each other.

Sesquizygotic twins are a relatively new concept for the types of multiple pregnancies. One of the studies shows that two different sperm cells fertilize a divided egg cell. It has the characteristic of both fraternal and identical twins where the baby is almost identical, but conceived from two sperm.

Causes of Multiple Pregnancy

One of the causes of multiple pregnancies is IVF or in vitro fertilization. There are cases where there are two embryos that sit in the uterus, one from the IVF where a fertilized cell is transferred to the uterus, and the other by natural conception.

It has also been observed that women who are older than 35 are more likely to have multiple pregnancies. Older women have higher chances of releasing more than one egg cell during their cycle, which also increases the chances of multiple pregnancies.

At this point, doctors know little about the direct causes for identical and sesquizygotic twins. But there are a few conditions that increase the likelihood of multiple births.

Conditions for Multiple Pregnancies

The following conditions increase the chances of multiple births. But remember, there is no 100% guarantee that these will lead to twins:

  • Women aged 30 and up need higher levels of estrogen to function, which increases the chance to produce and release more than 1 egg cell
  • If there is a history of twins in the family, especially if the woman has a twin.
  • If the previous pregnancy is twins, it has a higher chance to conceive twins in the next.
  • Race affects the chances of having multiple pregnancies. African women have the highest and Asian women are the lowest chances of multiple pregnancies.
  • Fertility treatment such as ovulation medications and IVF gives a higher chance for conceiving and multiple pregnancies.

Risks and Complications of Multiple Pregnancies

There are a lot of risks and complications during multiple pregnancies. Having one is already a stretch for a woman’s body. Make sure to consult your doctor regularly especially in cases of multiple pregnancies, to help you carry and deliver your baby safely.

Gestational diabetes and hypertension – Conditions affect the health and growth of the twins.

Preterm birth – Babies are not fully developed during delivery which may cause low birth weights or defects

Anemia – mothers need two times more iron to support multiple pregnancies

Twin-twin transfusion – An imbalance in the transfer of blood between identical twins, where one receives more than the other and can cause developmental issues with one of the babies.

Cesarean delivery – With two babies inside the uterus, it is harder for them to be in the right position during delivery.

Bleeding – It can occur in the vagina and cervix, which are caused by different factors such as:

  • Early opening of the cervix (Incompetent Cervix)
  • The placenta separates from the uterus and limits oxygen and nutrients supply for the babies (Placental abruption)
  • The placenta covers the cervix which makes delivery through the vagina harder (Placenta Previa)
  • Miscarriage

Key Takeaways

After learning more about the causes of multiple pregnancy, one will realize that multiple pregnancies can be both a challenging and rewarding experience. It is not easy to get pregnant with twins. And at the same time, a multiple pregnancy exposes women to significant risks and complications. Women expecting twins should regularly visit their doctors to ensure a safe delivery.

Learn more about other Conception Topics here. 


Hello Health Group does not provide medical advice, diagnosis or treatment.

Medically reviewed by

Jobelle Ann Dela Cruz Bigalbal, MD

General Practitioner

Written by Elaine Felicitas · Updated Jun 10, 2021

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