The presence of two developing fetuses inherently changes the risk profile of a pregnancy, necessitating specialized care and planning. Determining the optimal delivery time involves balancing the risks of prematurity for the infants against the risks of complications if the pregnancy continues too long. Medical guidance targets a delivery window where the risk of stillbirth begins to outweigh the benefits of further development in the womb. The safest delivery time depends heavily on specific biological factors, primarily how the twins share a placenta.
Increased Risk of Preterm Birth in Twin Pregnancies
Twin pregnancies are significantly more likely to result in preterm birth, which is defined as delivery before 37 weeks of gestation. Approximately 60% of twins are born prematurely, compared to about 10% of singletons. The primary cause for this increased rate is the physical overdistention of the uterus by two growing fetuses, two placentas, and an increased volume of amniotic fluid.
This mechanical stretching can trigger labor sooner than in a singleton pregnancy. The increased placental mass also leads to a higher incidence of complications like preeclampsia or placental abruption. These complications often require doctors to perform a medically-indicated preterm delivery to protect the health of the mother and babies. Premature rupture of membranes is also far more common in twin gestations, leading to spontaneous preterm labor and delivery.
Recommended Gestational Age for Delivery
The most important factor determining the safest delivery timing for twins is chorionicity, which describes whether the twins have one shared or two separate placentas. While the risk of stillbirth increases with advancing gestation in all twin pregnancies, the timing of this risk differs based on chorionicity.
Dichorionic-Diamniotic (Di/Di) twins, who have two separate placentas and amniotic sacs, have the lowest risk profile. For uncomplicated Di/Di twins, the recommended delivery window is between 37 weeks, 0 days and 38 weeks, 6 days of gestation. Delivering beyond this window increases the risk of perinatal death without providing a benefit from continued growth.
Monochorionic-Diamniotic (Mono/Di) twins share a single placenta but have separate amniotic sacs, placing them at a higher risk for complications like Twin-to-Twin Transfusion Syndrome (TTTS). For these uncomplicated twins, the recommended delivery window is earlier, generally between 36 weeks, 0 days and 36 weeks, 6 days. Delivery in this tighter window balances the risk of stillbirth, which rises after 36 weeks, against the risks associated with late preterm birth.
Monochorionic-Monoamniotic (Mono/Mono) twins are the rarest and highest-risk type, sharing both a placenta and a single amniotic sac. The primary concern is the risk of life-threatening umbilical cord entanglement as the pregnancy progresses. Delivery is typically recommended much earlier, between 32 weeks, 0 days and 33 weeks, 6 days, often by Cesarean section. This timing is chosen because the risk of fetal death from cord complications outweighs the risks of prematurity.
Neonatal Outcomes and Prematurity Risks
The strict gestational age recommendations exist because the risks of neonatal morbidity are substantially higher the earlier the delivery occurs. Twins born moderately preterm (32 to 33 weeks) or late preterm (34 to 36 weeks) face increased health complications compared to twins born at term (37 weeks or later).
The most common issue is Respiratory Distress Syndrome (RDS), caused by immature lungs lacking sufficient surfactant. Preterm twins also face challenges with temperature regulation, maintaining blood sugar levels, and feeding, often requiring feeding tubes.
These complications frequently necessitate a stay in the Neonatal Intensive Care Unit (NICU), with longer stays required for those born moderately or late preterm. Other serious risks include necrotizing enterocolitis (severe intestinal damage) and intraventricular hemorrhage (bleeding in the brain). The risk of these adverse outcomes decreases dramatically with each additional week the twins remain in the womb.
Monitoring Twin Pregnancies Prior to Delivery
To ensure the twins remain healthy until the planned delivery date, an intensive monitoring schedule is required compared to singleton pregnancies. Frequent ultrasounds are a primary tool, often beginning in the first trimester to determine chorionicity and assess fetal growth.
For monochorionic twins, who share a placenta, ultrasounds are performed every two weeks starting around 16 weeks to screen for complications like TTTS. All twin pregnancies also receive regular growth ultrasounds, typically every four weeks, to check for signs of Fetal Growth Restriction (FGR).
As the pregnancy nears the planned delivery window, additional surveillance may include non-stress tests (NSTs) and biophysical profiles to monitor the twins’ well-being. Cervical length measurements may also be performed to assess the risk of spontaneous preterm birth. This constant monitoring allows the medical team to intervene safely if a complication arises, potentially requiring an earlier delivery than initially planned.