Generally, a single pregnancy carries only one fetus, making multiple pregnancies a special phenomenon in human reproduction, such as the widely publicized birth of quintuplets. Due to advancements in assisted reproductive technologies and the use of ovulation-inducing drugs in recent years, the incidence of multiple pregnancies has significantly increased.In China, the ratio of twin to singleton births is 1:66-104. Twin pregnancies are more likely to occur in women with a family history of twins, those who have had multiple pregnancies, and older women. In recent years, due to the application of in vitro fertilization (IVF) technology and the use of ovulation-inducing drugs, the incidence of twins accounts for approximately 1% of all newborns.Statistics indicate that the average gestation period for twin pregnancies is 260 days, with 30% resulting in preterm birth. Approximately 42%-55% of fetuses weigh less than 2500g, and 10%-15% weigh under 1500g. The perinatal mortality rate reaches 10%-15%. These figures clearly demonstrate the significant risks associated with carrying twins.
1. How are twins formed?
Dizygotic twins occur when two eggs are released and fertilized separately, accounting for the majority of twin pregnancies. Each twin has its own amniotic sac and placenta. They may share the same sex or be different, with distinct appearances and temperaments. Many twins are the common boy-girl pairs.
Fraternal twins, however, develop from a single fertilized egg that splits into two embryos. They share identical genetic makeup but differ in appearance and temperament. Such siblings are often indistinguishable to others.
2. How can you determine if you're carrying twins?
With today's advanced medical technology, diagnosing twins is relatively straightforward.During prenatal visits, doctors first inquire about family history of multiple births, pre-pregnancy use of ovulation-inducing drugs, or IVF procedures. Upon abdominal palpation or uterine size assessment, the uterus may appear significantly larger than expected for gestational age, with increased abdominal tension. Occasionally, polyhydramnios (excess amniotic fluid) may be detected, along with multiple small limbs or two heads/two buttocks.When listening to fetal heart sounds, the range is broad, with two distinct heartbeats of different frequencies audible at different locations. Typically, the heart rates of the two fetuses differ by more than 10 beats per minute. Pregnancy symptoms are often more severe, weight gain is rapid, and fetal movements are frequent.At this stage, doctors can further confirm the diagnosis through ultrasound examination, typically identifying twin pregnancies between 12 and 15 weeks gestation. During mid- and late-pregnancy, as both fetuses develop, the uterus enlarges significantly, stretching the abdominal skin taut. The enlarged uterus causes the stomach to shift laterally, leading to discomfort after eating even small amounts and limiting food intake. Simultaneously, the diaphragm rises, compressing the heart and lungs, resulting in palpitations and shortness of breath.The enlarged uterus compresses the inferior vena cava, obstructing venous return. This can cause edema in the lower limbs and perineum, sometimes accompanied by varicose veins.
3. Are there greater risks with twin pregnancies compared to singleton pregnancies?
First, morning sickness tends to be more severe in twin pregnancies. Severe nausea and vomiting preventing adequate nutrition often lead to metabolic acidosis, requiring medical intervention for improvement.
From week 10 onward, the uterus enlarges faster than in singleton pregnancies, becoming especially noticeable after mid-pregnancy. By late pregnancy, the enlarged uterus may cause back pain, shortness of breath, fullness and reduced appetite, difficulty walking, varicose veins and swelling in the legs, hemorrhoid flare-ups, and other compression symptoms.
Blood volume increases more significantly in twin pregnancies than in singleton pregnancies, placing greater strain on the heart. Simultaneously, nurturing two fetuses demands higher levels of protein, iron, folic acid, and other nutrients. Due to reduced folic acid absorption and utilization during pregnancy, iron-deficiency anemia frequently occurs. Since the 1990s, China has implemented a policy of oral folic acid supplementation for pregnant women to prevent neural tube defects. Women carrying twins should pay particular attention to adequate folic acid intake.
Twin pregnancies also carry a higher risk of preeclampsia, with edema often appearing earlier. Headaches and dizziness should raise suspicion of preeclampsia, as untreated cases can progress to preeclampsia or eclampsia, threatening both maternal and fetal lives.
Due to the larger placenta in twin pregnancies, placenta previa and low-lying placenta occur more frequently, often causing antepartum hemorrhage. Painless bleeding during pregnancy warrants immediate medical attention. Concurrent conditions like polyhydramnios and fetal malformations may also arise.In twin pregnancies, uterine distension and increased pressure heighten the risk of premature rupture of membranes and preterm labor. Rates of malpresentation, intrauterine fetal death, and intrauterine growth restriction are significantly higher than in singleton pregnancies.
Fetal presentations at delivery in twin pregnancies vary widely. Both fetuses may be cephalic, or one may be breech while the other is cephalic. This increases the risk of obstructed labor, known as cephalic collision or fetal entanglement, which can endanger fetal life. Due to excessive uterine distension and overstretched muscle fibers, primary uterine atony is common, leading to prolonged labor and fetal asphyxia.Abnormal fetal presentation in twins, especially when combined with polyhydramnios, increases intrauterine pressure, heightening the risk of premature rupture of membranes and cord prolapse, both of which threaten fetal life.
After delivery of the first fetus, the sudden reduction in uterine cavity volume can shrink the placental attachment surface, leading to premature placental abruption before delivery of the second fetus.
Postpartum hemorrhage occurs due to the enlarged uterus and weakened elasticity of muscle fibers, impairing uterine contraction force and preventing closure of uterine sinuses. Twin pregnancies often involve anemia and reduced resistance. With two vaginal deliveries, the extensive endometrial trauma increases susceptibility to puerperal infection.
4.Fetofetal Transfusion Syndrome in Twin Pregnancies
Fetofetal transfusion syndrome in twin pregnancies is associated with vascular anastomoses between the placentas of the two fetuses. In addition to arteriovenous anastomoses, arterial-arterial anastomoses are also believed to exist. This allows one fetus to supply its own blood to the other through these anastomoses, causing the donor fetus to continuously transfer blood to the recipient fetus. The recipient fetus gradually develops hypovolemia, anemia,resulting in smaller size and lower birth weight, resembling intrauterine growth restriction. The recipient fetus, however, becomes larger with enlargement of the heart, liver, kidneys, pancreas, and adrenal glands. The high blood volume increases fetal urine output, leading to polyhydramnios. Both fetuses face life-threatening risks.
5. Do twin pregnancies require increased food intake?
During twin pregnancies, mothers must nourish two fetuses simultaneously, necessitating higher intake of protein, vitamins, calcium, iron, and other nutrients compared to singleton pregnancies. Expectant mothers often develop anemia due to inadequate nutritional intake and are prone to edema, hypertension, and other symptoms of pregnancy-induced toxemia in the late stages. Therefore, mothers carrying twins must ensure a balanced diet, eat well and sufficiently,eat smaller, more frequent meals, enhance nutritional intake, and supplement with iron and calcium. Due to abdominal distension and excessive tension, twin pregnancies often fail to reach full term, leading to preterm birth and difficult labor. Therefore, after confirming a twin pregnancy, ensure adequate rest, avoid overexertion, attend regular prenatal checkups, receive perinatal care, and follow medical advice to prevent premature birth and reduce complications.
6. What aspects require extra attention for twin pregnancies?
During pregnancy, schedule regular prenatal checkups to confirm the twin pregnancy early. Focus on nutritional enhancement, ensuring a balanced intake of essential nutrients to prevent anemia and preeclampsia.Avoid overexertion in late pregnancy. Increase bed rest after mid-pregnancy to promote fetal weight gain, reduce preterm birth, and lower perinatal mortality rates. If significant edema develops, moderately increase protein intake from sources like meat, eggs, milk, and soy products while limiting salt consumption.Refrain from sexual intercourse. Prioritize left-side lying positions; avoid sitting, semi-sitting, or supine postures. Elevate lower limbs during severe edema, using pillows for support during nighttime rest. Partners should provide special care, assisting with tasks like putting on shoes and socks, offering support while walking, and reducing physical exertion.