Multiple Pregnancy
Medically Reviewed by Dr Sravya, MBBS, MS
Introduction
Multiple pregnancy, also known as multiple gestation, refers to a pregnancy in which a woman is carrying two or more fetuses simultaneously in her womb. These fetuses can be of the same or different genders and can be either identical (monozygotic) or fraternal (dizygotic) twins. This text will take you deep into the types of multiple pregnancy.
What are the types of multiple pregnancy
Multiple pregnancies can be classified based on the number of fetuses and their zygosity (whether they are identical or fraternal).
- Dichorionic-Diamniotic (DCDA): This is the most common type of multiple pregnancy and occurs when each fetus has its own chorionic and amniotic sacs. It typically happens in fraternal twins or higher-order multiple pregnancies.
- Monochorionic-Diamniotic (MCDA): In this type, the fetuses share one chorionic sac but have their own amniotic sacs. It occurs when a single fertilized egg (zygote) splits early during development.
- Monochorionic-Monoamniotic (MCMA): In this rare and high-risk type, the fetuses share both the chorionic and amniotic sacs. It occurs when the zygote completely splits at a later stage of development than in MCDA twins.
- Conjoined Twins: Conjoined twins are a rare and complex types of multiple pregnancy where the fetuses are physically connected to each other. This occurs when the zygote does not fully separate during development.
- Higher-Order Multiples (Triplets, Quadruplets, etc.): This category includes pregnancies with three or more fetuses. They can be DCDA, MCDA, MCMA, or a combination, depending on the number of chorionic and amniotic sacs shared by the fetuses.
What are the causes of multiple pregnancy
Multiple pregnancies occur when a woman carries two or more fetuses in her womb simultaneously. The main causes of multiple pregnancies are related to the release and fertilization of multiple eggs during ovulation. There are two primary mechanisms that lead to multiple pregnancies:
Fraternal (Dizygotic) Twins or Higher-Order Multiples: Fraternal twins, triplets, or higher-order multiples result from the fertilization of two or more separate eggs (ova) by two or more different sperm cells during a single ovulation cycle. Each fertilized egg develops into its own fetus, and each fetus has its own set of genetic material.
Causes:
- Hyperovulation: In some women, more than one egg is released during ovulation, increasing the chances of multiple eggs being fertilized by different sperm cells.
- Genetics: A family history of fraternal multiples can increase the likelihood of having fraternal twins.
Identical (Monozygotic) Twins or Higher-Order Multiples: Identical twins, triplets, or higher-order multiples occur when a single fertilized egg (zygote) divides into two or more embryos during the early stages of development. Each embryo shares the same genetic material.
Causes:
- Spontaneous Division: Sometimes, the zygote spontaneously splits into two or more embryos. The exact reason for this spontaneous division is not fully understood.
- Timing of Division: The timing of the embryo's division determines the type of placenta and amniotic sacs shared by the multiples (monochorionic or dichorionic, monoamniotic or diamniotic).
It is important to note that certain factors can increase the likelihood of having a multiple pregnancy:
- Age: Women over the age of 30, especially those in their late 30s or 40s, are more likely to release multiple eggs during ovulation, increasing the chances of fraternal multiples.
- Family History: Having a family history of multiple pregnancies, especially on the mother's side, can increase the likelihood of having fraternal twins.
- Race and Ethnicity: Some ethnic groups, such as Africans and African-Americans, tend to have a higher incidence of multiple pregnancies.
- Assisted Reproductive Technologies (ART): The use of fertility treatments like in vitro fertilization (IVF) or ovulation-stimulating medications can increase the chances of having multiple pregnancies, both fraternal and identical.
What are the symptoms of multiple pregnancy?
Multiple pregnancies can be associated with some specific symptoms in addition to typical pregnancy symptoms experienced by women carrying a single fetus. However, it’s important to note that the symptoms of multiple pregnancies can vary widely among individuals, and not all women with multiple pregnancies will experience all of these signs.
To avoid recurring infections, it is critical to treat any underlying diseases or factors, such as diabetes or hormone defects.
Some common symptoms of multiple pregnancies include:
- More Pronounced Pregnancy Symptoms: Women with multiple pregnancies often experience more intense and pronounced pregnancy symptoms such as morning sickness, fatigue, breast tenderness, and frequent urination.
- Rapid Weight Gain: Due to the presence of more than one fetus, women with multiple pregnancies may gain weight more rapidly than those with single pregnancies.
- Larger Uterus: The uterus may be larger than expected for the gestational age, as it accommodates multiple fetuses.
- Multiple Fetal Movements: Women carrying multiple fetuses may feel more frequent and pronounced fetal movements.
- Excessive Nausea and Vomiting: Some women with multiple pregnancies may experience more severe morning sickness (hyperemesis gravidarum).
- Increased Appetite: The body's demand for nutrients is higher in multiple pregnancies, leading to increased hunger.
- Swollen or Tender Breasts: Breasts may become more swollen and tender as a result of hormonal changes.
- Shortness of Breath: As the uterus expands to accommodate multiple fetuses, it can put pressure on the diaphragm, leading to shortness of breath.
- Abdominal Discomfort: Women with multiple pregnancies may experience more significant abdominal discomfort and stretching sensations.
- Fetal Heartbeats: During prenatal check-ups, healthcare providers may detect more than one fetal heartbeat, indicating a multiple pregnancy.
- Higher Levels of hCG: Levels of the hormone human chorionic gonadotropin (hCG) may be higher than average in multiple pregnancies, which can sometimes be detected through blood tests.
How multiple pregnancy can be diagnosed
The diagnosis of a multiple pregnancy is typically made through prenatal screening and imaging tests. Healthcare providers use various methods to confirm the presence of multiple fetuses and to determine their type (identical or fraternal) and the number of placentas and amniotic sacs they share.
The main diagnostic methods for multiple pregnancies include:
- Ultrasound: Ultrasound is the most common and reliable method used to diagnose multiple pregnancies. It uses sound waves to create real-time images of the developing fetuses in the womb. During the ultrasound, the healthcare provider can see the number of fetuses, their positions, and their development stage. The ultrasound can also reveal if the fetuses share a placenta and/or an amniotic sac, helping to differentiate between identical and fraternal multiples.
- Blood Tests: Blood tests can measure the levels of certain hormones, such as human chorionic gonadotropin (hCG) and alpha-fetoprotein (AFP), which can be higher than normal in multiple pregnancies. However, blood tests alone cannot confirm the presence of multiple fetuses; they are usually used in conjunction with other diagnostic methods.
- Prenatal Screening: Prenatal screening tests, such as the first-trimester combined screening or the quad screen, can provide information about the risk of having multiple pregnancies. These tests assess factors like maternal age, hCG levels, and other markers to estimate the likelihood of multiple fetuses.
- Physical Examination: A physical examination by a healthcare provider may reveal an enlarged uterus, which can be an indication of a multiple pregnancy. However, this is not a definitive diagnosis and needs to be confirmed through ultrasound.
- Family History: A family history of twins or higher-order multiples can raise suspicion for a multiple pregnancy. However, a family history alone is not enough to confirm the presence of multiple fetuses.
How multiple pregnancy can be prevented
Preventing multiple pregnancies entirely may not always be possible, as some factors leading to multiple pregnancies are beyond individual control, such as genetics or the spontaneous splitting of an embryo. However, there are certain measures and considerations that can help reduce the likelihood of having multiple pregnancy:
- Preventing Ovulation Stimulation: Multiple pregnancies can occur as a result of fertility treatments that stimulate ovulation, such as in vitro fertilization (IVF) or ovulation-stimulating medications. To minimize the risk of multiple pregnancies with these treatments, healthcare providers can carefully adjust the dosage and closely monitor the response to the medications.
- Family Planning: For couples trying to conceive naturally, it is not possible to prevent fraternal multiple pregnancies entirely, as hyperovulation (releasing more than one egg) is a natural process. However, couples can consider family planning methods to space out pregnancies and reduce the likelihood of having multiple pregnancies close together.
- Using Contraception: Using effective contraception can help prevent unintended pregnancies, including multiple pregnancies. Women who are not ready to conceive or wish to avoid pregnancy should discuss and choose a suitable contraceptive method with their healthcare provider.
- Age Considerations: Women over the age of 30, especially those in their late 30s or 40s, have a higher likelihood of releasing multiple eggs during ovulation, increasing the chances of fraternal multiples. Considering family planning options and discussing pregnancy risks with a healthcare provider can be beneficial.
- Health and Lifestyle Factors: Maintaining a healthy lifestyle and managing certain health conditions can contribute to overall reproductive health. Women should avoid smoking, excessive alcohol consumption, and drug use and manage chronic conditions such as diabetes and obesity, which may affect fertility and pregnancy outcomes.
- Genetic Screening: In cases where there is a family history of fraternal twins, couples may opt for genetic counseling and screening to understand their likelihood of having fraternal multiples. However, it's important to remember that identical twins result from spontaneous splitting and cannot be predicted or prevented.
It is essential for individuals and couples to have open and informed discussions with their healthcare providers about their reproductive goals and concerns. Healthcare providers can provide personalized guidance and recommendations based on each individual’s medical history and circumstances. Remember that while some factors can influence the likelihood of multiple pregnancies, certain aspects of multiple pregnancies are beyond control, and embracing proper prenatal care and management is essential for the well-being of both the mother and the fetus.