Understanding Multiple Pregnancies: Causes, Types, and Care

Discovering that you are expecting more than one baby can bring excitement along with many questions about your health and pregnancy. Whether you are expecting twins, triplets, or more, multiple pregnancy requires closer monitoring because your care team needs to track the growth and well-being of each baby. Understanding multiple pregnancies, how they occur, what to expect at different stages, and how doctors manage potential risks can help you feel more prepared for the journey ahead. This guide explains the causes and types of multiple pregnancies, important week-by-week milestones, possible complications, and the care that can help support a healthy pregnancy.

What Are Multiple Pregnancies?

Multiple pregnancy occurs when a woman carries more than one fetus in her uterus at the same time. These are commonly referred to as twins (two fetuses), triplets (three fetuses), or higher-order multiples such as quadruplets or quintuplets.

In natural conception, multiple pregnancy can occur when the ovaries release more than one egg during ovulation and multiple eggs become fertilised and implant in the uterus. A multiple pregnancy can also occur when a single fertilised embryo splits into two embryos, resulting in identical twins.

Multiple pregnancies can also occur if the woman has taken medicines for formation of egg (ovulation induction) for either timed intercourse or IUI. These medicines can result in formation of more than one follicle in a cycle, thereby increasing the chances of multiple pregnancies.

In IVF, multiple pregnancy can occur when more than one embryo is transferred. However, there is a small risk that even after a single embryo is transferred in IVF, twins can occur due to the splitting of the embryo after transfer.

Natural Causes of Multiple Pregnancy

Understanding the causes of multiple pregnancies also means knowing what can increase the likelihood of conceiving more than one baby. Several biological and genetic factors can influence this likelihood:

• Advanced Maternal Age: Women with advanced maternal age produce higher baseline levels of follicle-stimulating hormone (FSH). Elevated FSH levels increase the likelihood that the ovaries will release two or more eggs during a single menstrual cycle.
• Family History and Genetics: A family history of fraternal twins, particularly on the mother's side, can increase the likelihood of hyperovulation, a tendency to release more than one egg during ovulation.
• Ethnicity and Demographics: Global health records indicate that natural multiple conception rates vary across different ethnicities and geographic populations due to baseline genetic factors.

How Fertility Treatments Influence Multiple Pregnancy Risk

Fertility treatments increase multiple pregnancy rates by intentionally stimulating the ovaries or introducing more than one embryo into the reproductive tract.

During treatments such as intrauterine insemination (IUI) combined with ovulation induction, medications encourage the ovaries to mature multiple eggs simultaneously. If sperm fertilize more than one mature egg, fraternal multiples develop.

Assisted reproductive technology (ART), including IVF, can also result in multiple pregnancy when more than one embryo is transferred to the uterus. However, IVF does not always result in twins. Modern fertility care increasingly uses elective single embryo transfer (eSET) when appropriate, transferring one embryo while preserving additional suitable embryos for future use. This embryo transfer procedure helps reduce the likelihood of multiple pregnancy while still allowing patients to pursue IVF treatment.

Types of Multiple Pregnancy

Doctors classify the types of multiple pregnancies as monozygotic (identical) or dizygotic (fraternal) based on how the embryos develop. Higher-order multiples, such as triplets and quadruplets, can result from either mechanism or a combination of both.

1. Dizygotic (Fraternal) Twins

   Dizygotic twins develop when two separate eggs are fertilised by two separate sperm cells in the same reproductive cycle. These twins share about 50% of their genetic material, similar to other biological siblings, and can be the same or different biological sexes. Each twin develops with a separate placenta (dichorionic) and a separate amniotic sac (diamniotic).

2. Monozygotic (Identical) Twins

   Monozygotic twins develop when a single fertilised egg splits into two embryos early in development. These twins share nearly all of their genetic material and are usually the same biological sex. Depending on when the fertilised egg splits, the twins may develop separate placentas or share one placenta (monochorionic). They may also have separate or shared amniotic sacs.

3. Higher-Order Multiples

   Higher-order multiples include triplets, quadruplets, quintuplets, and other pregnancies involving three or more fetuses. These pregnancies can develop from multiple fertilised eggs, one fertilised egg splitting into several embryos, or a combination of both processes. As a result, higher-order multiples can include both identical and fraternal siblings and can have different combinations of shared or separate placentas and amniotic sacs.

In multiple pregnancies, chorionicity refers to the number of placentas supporting the fetuses, while amnionicity refers to the number of amniotic sacs. Doctors usually determine these features during an early ultrasound because pregnancies in which babies share a placenta may require closer monitoring for complications related to shared blood circulation.

Multiple Pregnancy Week by Week Timeline

Multiple pregnancy is categorized as high risk pregnancy and requires closer medical and antenatal monitoring. The monitoring schedule may vary based on the type of multiple pregnancy and the health of the mother and babies.

Multiple Gestation Complications

Carrying more than one baby increases the chance of certain pregnancy complications, which is why multiple pregnancies usually require closer monitoring.

Twin pregnancies are significantly more likely to result in preterm birth than singleton pregnancies. A clinical review titled "Spontaneous preterm birth prevention in multiple pregnancy" published on PubMed Central reports that around 50% of twin pregnancies result in birth before 37 weeks, compared with about 10% of singleton pregnancies. The timing and route of delivery can vary depending on the type of twin pregnancy, placental arrangement, and whether complications develop.

Key complications of multiple pregnancies include:

• Preterm Labor and Birth: Increased uterine stretching due to multiple pregnancies can trigger early contractions, causing babies to arrive before their organs fully mature.
• Gestational Hypertension and Preeclampsia: Women carrying multiples have a higher risk of developing high blood pressure and preeclampsia, a pregnancy-related condition that can affect the mother's organs and the babies' health.
• Gestational Diabetes: Multiple pregnancies increase the risk of developing diabetes during pregnancy, which may require closer monitoring of blood sugar levels and dietary management.
• Maternal Anemia: The increased nutritional demands of carrying more than one baby can raise the risk of iron-deficiency anaemia during pregnancy.
• Twin-to-Twin Transfusion Syndrome (TTTS): This complication can occur in identical twins who share a placenta. Shared blood vessels within the placenta can cause an unequal distribution of blood between the babies.
• Fetal Growth Restriction (FGR): Shared placental space can cause one or both babies during multiple pregnancy to grow at a slower rate than standard growth charts expect.

Management and Treatment of Multiple Pregnancy

Multiple pregnancy is not an illness. It only requires closer monitoring and personalised care to support the health of the mother and each fetus throughout pregnancy.

1. Frequent Prenatal Examinations: Expectant mothers with multiple pregnancies require more frequent clinical visits and ultrasound assessments mothers carrying a single baby.

2. Targeted Nutritional Support: A balanced diet with adequate calories, protein, iron, folic acid, and other essential nutrients help meet the increased nutritional demands of pregnancy. Your healthcare provider may recommend supplements based on your individual needs.

3. Rest and Lifestyle Modifications: Reducing high-impact activities like physical activity, work, travel, or daily routines during the third trimester helps manage cervical strain and physical discomfort while carrying multiple pregnancies.

4. Specialized Delivery Planning: Obstetricians determine the safest delivery route based on fetal positions, placental locations, and gestational age. While vaginal birth is common when the lower twin presents head-down, C-section births are often planned for complex twin presentations or triplets.

If you have conceived through fertility treatment or have recently learned that you are expecting twins or more, understanding multiple pregnancies can help you feel better prepared for the monitoring and care ahead. Discussing your pregnancy with an experienced specialist at Nova IVF Fertility can help you understand what to expect and plan care based on your individual circumstances.

Frequently Asked Questions

What are the early signs of multiple pregnancies?

Multiple pregnancies can cause stronger early pregnancy symptoms because pregnancy hormone levels may be higher. Symptoms can include significant nausea or vomiting, fatigue, breast tenderness, and faster-than-expected weight gain. However, these symptoms can also occur in singleton pregnancies. An ultrasound is the most reliable way to confirm whether you are carrying more than one baby.

When are twins born naturally?

Twin pregnancies reach full term at 37 weeks, which is earlier than the standard 40-week timeline for single babies. Due to less space in the uterus and natural signals from the body, many twin pregnancies go into labor spontaneously between 35 and 37 weeks.

Are miscarriages more common with twins?

Multiple pregnancies have a higher risk of pregnancy loss than singleton pregnancies. One more possible outcome is “vanishing twin syndrome”, in which an early ultrasound shows more than one pregnancy but a later scan shows that one embryo is no longer developing and which will eventually get resorbed and disappear, leaving only a single baby to grow.

Can diet or lifestyle affect the chances of multiple pregnancy?

Diet and lifestyle have little influence on whether a woman naturally conceives twins. Factors such as maternal age, family history, and fertility treatment have a strong influence on the likelihood of multiple pregnancy. Maintaining a healthy lifestyle is still important for supporting pregnancy health.

How early can multiple pregnancy be detected on ultrasound?

A transvaginal ultrasound can detect multiple gestational sacs as early as 5 to 6 weeks of pregnancy. Clear confirmation of separate heartbeats and placental structures typically occurs between 6 and 8 weeks of pregnancy.