A twin pregnancy requires balancing the risks of remaining in the womb against the hazards of an early birth. Determining the safest delivery point involves assessing the mother’s health and the babies’ maturity. A safe delivery is not a fixed date, but a calculated window where the risk of complications from staying inside outweighs the risks of being born. This window is highly individualized, depending on how the twins share their placenta and amniotic sacs.
Recommended Delivery Windows Based on Twin Type
The structure of the pregnancy dictates the recommended target delivery week for twins. This structure is categorized by chorionicity (number of placentas) and amnionicity (number of amniotic sacs). Medical guidelines establish target delivery windows for uncomplicated pregnancies based on these factors to minimize stillbirth risks while maximizing fetal development.
Dichorionic/Diamniotic (Di/Di) twins have two separate placentas and two separate sacs, representing the lowest risk twin pregnancy. The standard recommendation is to plan delivery between 37 weeks and 38 weeks and six days of gestation. Continuing the pregnancy past 38 weeks increases the risk of stillbirth without improving outcomes, so elective delivery is advised within this range.
Monochorionic/Diamniotic (Mo/Di) twins share one placenta but have two separate sacs. This introduces the risk of unequal blood flow distribution and complications like Twin-to-Twin Transfusion Syndrome (TTTS). Therefore, the target delivery window is earlier than Di/Di twins. Uncomplicated Mo/Di twins are typically delivered electively between 36 and 37 weeks of gestation.
The highest risk scenario involves Monochorionic/Monoamniotic (Mo/Mo) twins, who share a single placenta and a single amniotic sac. The shared sac creates a danger of umbilical cord entanglement, which can restrict blood flow. To manage this specific risk, delivery is advised much earlier, usually between 32 and 34 weeks of gestation.
Due to the significant cord risk, Mo/Mo pregnancies often require continuous inpatient monitoring starting as early as 24 to 28 weeks. This allows for immediate intervention if fetal distress occurs. These recommendations are guidelines for otherwise uncomplicated pregnancies and are subject to change based on regular monitoring.
The Risks of Prematurity
The goal of carrying a twin pregnancy as long as safely possible is to allow the fetuses to reach maturity outside the uterus. Birth before 37 weeks is considered preterm. The earlier the birth, the higher the likelihood of needing specialized care in a neonatal intensive care unit (NICU). More than three in five twin pregnancies result in a preterm birth, a rate significantly higher than in singleton pregnancies.
One common issue for premature newborns is Respiratory Distress Syndrome (RDS). This occurs because the lungs have not fully developed the ability to produce surfactant, which helps keep the air sacs open. Without sufficient surfactant, babies may struggle to breathe and require mechanical assistance. Preterm infants also face challenges with temperature regulation due to less body fat and an immature central nervous system.
Neurological development is another concern, as early birth can affect the developing brain. One potential complication is Intraventricular Hemorrhage (IVH), which is bleeding into the fluid-filled areas of the brain. Although short-term morbidity risks may be similar to singletons born at the same gestational age, twins are born earlier on average, increasing their overall risk exposure.
Prematurity can also lead to long-term health issues extending into childhood. These include a higher occurrence of conditions such as cerebral palsy, intellectual and developmental delays, and impairments in vision or hearing. Delaying delivery until the recommended window mitigates these risks by allowing maximum time for organ maturation.
When Doctors Must Deliver Twins Early
Despite the known risks of prematurity, sometimes the danger of continuing the pregnancy outweighs the risks of an early birth. These situations involve complications that threaten the health or life of the mother or one or both fetuses. The decision is a careful calculation of which environment—inside or outside the womb—offers the better chance of survival and health.
One specific complication in monochorionic twins is Twin-to-Twin Transfusion Syndrome (TTTS). This involves an imbalance in blood flow across the shared placenta, causing one twin to receive too much blood and the other too little. TTTS can severely strain the cardiovascular systems of both fetuses. It may necessitate early delivery to save one or both lives, sometimes following in-utero surgical intervention.
Maternal conditions can also trigger the need for an early delivery, such as severe preeclampsia or HELLP syndrome. These involve dangerously high blood pressure and organ damage. Since these disorders progress rapidly, delivery is often the only definitive treatment to prevent serious illness or death for the mother. Similarly, a placental abruption, where the placenta prematurely separates from the uterine wall, requires immediate delivery as it cuts off the babies’ oxygen supply.
Fetal growth restriction (FGR) or intrauterine growth restriction (IUGR) is another common indication for early delivery. This occurs when one or both twins are not growing as expected. If monitoring suggests the fetuses are not receiving adequate nourishment or oxygen, they may be safer in the NICU than in a compromised uterine environment. Depending on the severity of the growth restriction and abnormal blood flow, delivery may be planned as early as 30 to 34 weeks for Di/Di twins.