Multifetal gestation is the presence of > 1 fetus in the uterus.
In the United States in 2021, multifetal delivery rates were 31 twin births per 1,000 total births and 80 triplet and higher-order multiple births per 100,000 (1). Rates of twin pregnancies vary across countries and regions; they are highest in Africa, intermediate in the United States, Europe, and Australasia, and lowest in Asia and South America (2).
Risk factors for multifetal gestation include (3):
Use of assisted reproductive technologies (eg, in vitro fertilization)
Personal or family history of multifetal gestation
Increasing parity
Obesity
Increased maternal height (≥ 65 inches [164 cm])
Maternal age ≥ 35 years
Complications
Multifetal gestation increases the risk of (4):
Neonatal death, largely due to prematurity
The overdistended uterus tends to stimulate preterm labor, causing preterm delivery. Average gestational age at birth is (5):
Twins: 35 weeks
Triplets or higher: 31 weeks
In multifetal gestations, there may be variations in fetal presentation, position, or lie. The uterus may contract after delivery of the first child, partially shearing away the placenta (placental abruption) and increasing risk for the remaining fetuses. Sometimes uterine distention impairs postpartum uterine contraction, leading to atony and postpartum hemorrhage.
Some complications develop only in multifetal gestations. An example is twin-twin transfusion syndrome (when twins share the same placenta; this syndrome results in vascular communication between the two, which can lead to unequal sharing of blood).
References
1. Osterman MJK, Hamilton BE, Martin JA, Driscoll AK, Valenzuela CP: Births: Final Data for 2021. Natl Vital Stat Rep. 2023;72(1):1-53.
2. Monden C, Pison G, Smits J: Twin Peaks: more twinning in humans than ever before. Hum Reprod. 2021;36(6):1666-1673. doi:10.1093/humrep/deab029
3. Hoekstra C, Zhao ZZ, Lambalk CB, et al: Dizygotic twinning. Hum Reprod Update. 2008;14(1):37-47. doi:10.1093/humupd/dmm036
4. American College of Obstetricians and Gynecologists' Committee on Practice Bulletins: Multifetal Gestations: Twin, Triplet, and Higher-Order Multifetal Pregnancies: ACOG Practice Bulletin, Number 231. Obstet Gynecol. 2021;137(6):e145-e162. doi:10.1097/AOG.0000000000004397
5. Centers for Disease Control and Prevention, National Center for Health Statistics: National Vital Statistics System, Natality on CDC WONDER Online Database. Data are from the Natality Records for births occurring in 2023 through last month as compiled from data provided by the 57 vital statistics jurisdictions through the Vital Statistics Cooperative Program. Accessed March 13, 2024.
Diagnosis of Multifetal Gestation
Prenatal ultrasound
Multifetal gestation is suspected if the uterus is large for dates; it is confirmed on prenatal ultrasound. Ultrasonography can also determine whether each fetus in a multifetal gestation has a separate chorion and amnion. A pregnancy with a shared chorion (eg, monochorionic twins) or shared chorion and amnion (eg, monoamniotic twins) are at risk for twin-twin transfusion syndrome (resulting in asymmetric fluid distribution and growth between the fetuses).
Management of Multifetal Gestation
Prenatal monitoring for and prevention of complications
Cesarean delivery when indicated
Prenatal care is directed at evaluating fetal growth and monitoring for complications. Testing for gestational diabetes and monitoring for preeclampsia
For twin pregnancies, vaginal delivery is preferred if the presenting twin is in vertex presentation. Cesarean delivery is done for a nonvertex presenting twin or higher-order multiple gestations, or if delivery needs to be expedited for fetal or maternal indications.
Key Points
Multifetal gestations have increased risks to the pregnant patient and the fetus and neonate, including gestational diabetes, preeclampsia, preterm delivery, growth restriction, postpartum hemorrhage, and stillbirth or neonatal death.
If the uterus is large for gestational age, do an ultrasound to evaluate for multifetal gestation.
Monitor fetal growth and for complications as follows: test for diabetes, monitor for preeclampsia, and possibly do serial ultrasounds to check for cervical shortening in the second trimester and antepartum fetal surveillance (eg, biophysical profile) starting at 32 weeks.
Vaginal delivery of twins is preferred, if the presenting twin is in vertex presentation.
Deliver by cesarean for a nonvertex presenting twin, higher-order multiple gestation, or for other fetal or maternal indications.
