Twin Pregnancy

Symptoms

• More severe nausea and vomiting (hyperemesis gravidarum)
• Increased breast tenderness
• Greater fatigue
• Rapid or excessive weight gain in the first trimester
• Uterus larger than expected for gestational age (increased fundal height)
• Increased perception of fetal movement later in pregnancy
• More pronounced shortness of breath
• Increased constipation
• More pelvic pressure
• Increased back pain
• Severe headache (emergency symptom)
• Visual disturbances (emergency symptom)
• Severe pain below the ribs (emergency symptom)
• Sudden swelling of face, hands, or feet (emergency symptom)
• Regular, painful contractions before 37 weeks (emergency symptom)
• Rupture of membranes (water breaking) (emergency symptom)
• Vaginal bleeding (emergency symptom)
• Significant discrepancy in fetal movement between the twins (emergency symptom)
• Sudden increase in abdominal size (emergency symptom, may indicate polyhydramnios)

Causes & Risk Factors

• Dizygotic (Fraternal) Twinning: Occurs when two separate eggs are released and fertilized by two different sperm in the same cycle. Factors that increase the chance of this include genetic predisposition, increasing maternal age, and the use of Assisted Reproductive Technology (ART).
• Monozygotic (Identical) Twinning: Occurs when a single fertilized egg splits into two embryos. The exact reason for this splitting is largely unknown and is generally considered a random event.
• The timing of the embryo split for identical twins determines whether they share a placenta or amniotic sac:
• Splitting within 0-3 days after fertilization typically results in Dichorionic-Diamniotic (DCDA) twins.
• Splitting within 4-8 days after fertilization typically results in Monochorionic-Diamniotic (MCDA) twins.
• Splitting within 8-12 days after fertilization typically results in Monochorionic-Monoamniotic (MCMA) twins.
• Splitting after 13 days post-fertilization can result in conjoined twins, which is rare.
• Use of Assisted Reproductive Technology (ART), such as in-vitro fertilization (IVF) (especially with multiple embryo transfer) and ovulation induction medications (e.g., clomiphene citrate, gonadotropins). This is the most significant factor for fraternal twinning.
• Increasing maternal age, particularly over 35, as higher levels of follicle-stimulating hormone (FSH) can lead to the release of more than one egg.
• A family history of twinning on the mother's side, which increases the chance of fraternal twinning.
• Maternal race/ethnicity: highest rates in women of Black African ancestry, lowest in women of Asian ancestry, and intermediate rates in Caucasian women.
• Higher number of previous pregnancies (parity).
• Taller maternal height.
• Maternal Body Mass Index (BMI) over 30.
• Opting for single embryo transfer during ART can modify the risk of multiple pregnancies.
• Pre-conception BMI can be modified.

Diagnosis

• A patient's medical history, including use of Assisted Reproductive Technology (ART), family history of twins, or reports of exaggerated pregnancy symptoms.
• Physical examination findings such as a fundal height (measurement of the uterus) greater than expected for gestational age, hearing two distinct fetal heartbeats, or feeling more than two fetal poles (heads or bottoms). However, physical examination alone is not reliable for diagnosis.
• Ultrasound: This is the definitive and most important diagnostic tool.
• A first-trimester ultrasound, ideally between 11 weeks and 0 days to 13 weeks and 6 days, is critical.
• The ultrasound confirms the presence of two fetuses and determines their viability.
• Crucially, it determines chorionicity (number of placentas) and amnionicity (number of amniotic sacs), which is essential for risk assessment and management. Dichorionic twins show two separate placentas or a thick dividing membrane with a 'lambda sign' or 'twin peak sign'. Monochorionic twins show a single placental mass and a thin dividing membrane with a 'T-sign'. Monoamniotic twins have no dividing membrane.
• The ultrasound also helps establish gestational age based on the crown-rump length (CRL) of the larger twin.
• Nuchal translucency (NT) measurement can be performed for aneuploidy screening.
• Maternal serum analyte levels (e.g., hCG, alpha-fetoprotein) may be higher than in singleton pregnancies but are less reliable for screening.
• Non-invasive prenatal testing (NIPT) can be used for aneuploidy screening, though its performance may be slightly lower and test failure rates higher compared to singleton pregnancies.
• The diagnostic criteria for a twin pregnancy is the visualization of two fetuses on ultrasound examination.
• Current guidelines from organizations like ACOG and NICE recommend a first-trimester ultrasound to confirm viability, establish gestational age, and, most importantly, determine chorionicity.

Treatment Options

• Lifestyle and Nutrition:
• Increased caloric intake: An additional 300 kcal/day per fetus is a common recommendation, focusing on nutrient-dense foods.
• Increased weight gain: Guidelines suggest higher weight gain for twin pregnancies based on pre-pregnancy BMI (e.g., 37-54 lbs for normal weight, 31-50 lbs for overweight, 25-42 lbs for obese).
• Supplementation: Higher requirements for iron, folic acid, calcium, and other micronutrients. Iron supplementation is recommended to prevent anemia.
• Activity: May need to be modified as pregnancy progresses, with avoidance of strenuous activity in the third trimester.
• Medical (Antenatal Surveillance):
• Referral: All twin pregnancies should be managed by a specialist obstetric team.
• Frequency of Visits: More frequent antenatal visits than for singleton pregnancies.
• Ultrasound Surveillance: Growth scans every 4 weeks from 20 weeks for Dichorionic-Diamniotic (DCDA) twins. Growth scans and screening for Twin-to-Twin Transfusion Syndrome (TTTS) every 2 weeks from 16 weeks until delivery for Monochorionic-Diamniotic (MCDA) twins. Inpatient management from 24-28 weeks is often recommended for Monochorionic-Monoamniotic (MCMA) twins for intensive fetal monitoring (e.g., daily CTG).
• Fetal Aneuploidy Screening: Discussion of options including NIPT and combined first-trimester screening. Diagnostic testing (amniocentesis, CVS) is more complex.
• Preeclampsia Prevention: Low-dose aspirin is recommended from 12 weeks gestation.
• Preterm Birth Prevention: Cervical length screening may be supported for DCDA twins by some guidelines, but not routinely recommended by others. Progesterone is not generally recommended for unselected twin pregnancies. Cervical cerclage may be considered for women with a short cervix. Antenatal corticosteroids are administered to women at risk of preterm delivery before 34 weeks to promote fetal lung maturity.
• Timing and Mode of Delivery:
• Timing of delivery varies by chorionicity and guideline. For uncomplicated DCDA twins, delivery is often recommended between 37+0 and 38+6 weeks. For uncomplicated MCDA twins, delivery is often recommended between 34+0 and 37+6 weeks. For uncomplicated MCMA twins, planned delivery is often recommended between 32+0 and 34+0 weeks.
• Mode of delivery depends on chorionicity, fetal presentation (especially of the first twin), gestational age, and complications. Vaginal delivery may be an option if the presenting twin is head-down, typically after 32 weeks. Cesarean delivery is recommended for MCMA pregnancies (due to cord entanglement risk), if the first twin is not head-down, or for other standard obstetric reasons.
• Emergency Treatment:
• Management of acute complications such as severe preeclampsia, preterm labor, or acute TTTS.
• For severe TTTS, fetoscopic laser ablation of placental anastomoses is the primary in-utero treatment.

Frequently Asked Questions