Introduction

Multifetal gestations are associated with higher risks than their singleton counterparts. In 2021, twin births accounted for 21.3 per 1000 live births; triplet and higher-order births were 80 per 100,000 live births.[1] The recommended mode of delivery for twin gestations has been debated in the literature. Current American College of Obstetrics and Gynecology (ACOG) guidelines state that twin gestation, in general, is not an indication for a cesarean section.[2] There has been further debate regarding what types of twin pregnancies are candidates for vaginal delivery given the risks associated with a change in fetal lie after delivery of the first twin, risk of placental abruption due to the abrupt decompression of the uterus after delivery of the first twin, cord prolapse, and changes in cervical dilation that may hinder the delivery of the second twin.[3] The Twin Birth Study, the first large randomized controlled trial evaluating twin birth outcomes, found there was no increased risk of neonatal morbidity or mortality in patients who underwent vaginal delivery versus cesarean section.[4] However, the management of twin delivery is challenging for obstetricians due to issues associated with monitoring both twins during labor and the maneuvers that may be necessary to deliver the second twin.

Not all patients with a twin gestation should attempt a vaginal delivery. First, the patient should desire a trial of labor. The presenting twin must be in the cephalic position for vaginal delivery to be considered.[2] Twins with fetal growth discordance (greater than 20% difference in estimated fetal weight) preclude a patient from a vaginal delivery.[2] All conditions that are contraindications to vaginal delivery in singleton pregnancies will also prevent vaginal delivery in twin gestations. These conditions include cord prolapse, vertical incision on the uterus from prior surgery, placenta previa or accreta spectrum, infections such as current herpes outbreak, or fetal intolerance of labor.[5][6][7] The delivery of twins is determined by twin type and maternal and fetal conditions around the time of delivery.

Indications

Delivery planning of twins is dependent on twin types: monochorionic monoamniotic, monochorionic diamniotic, and dichorionic diamniotic. For more information regarding the pathophysiology of twinning or prenatal management, refer to StatPearls "Twin Births."[8] 

Monochorionic Monoamniotic Twins

Monoamniotic monochorionic (mo-mo) twins are rarely seen. The reported incidence is 8 per 100,000 pregnancies. Perinatal mortality is estimated to be between 30% and 40% due to high risks for fetal anomalies, twin reversed arterial perfusion syndrome (a-cardiac twinning), twin-twin transfusion syndrome, cord entanglement, or acute vascular events.[9][10][11]

Delivery planning of mo-mo twins is dependent upon fetal well-being and maternal comorbidities. Serial ultrasounds should begin at 16 weeks to assess fetal growth and amniotic fluid.[12] At 28 weeks, ultrasounds should be performed weekly until delivery; this antenatal testing can be performed as an inpatient or outpatient.[13] For uncomplicated mo-mo twins, delivery is recommended between 32 0/7 weeks and 34 0/7 weeks.[12]

The mode of delivery is controversial. Most centers opt for cesarean delivery due to the risk of cord accidents. There have been some published studies demonstrating that vaginal delivery can be considered with the appropriate candidates, although these were single-site studies with less than 50 participants.[14][15]

Monochorionic Diamniotic Twins

Monochorionic diamniotic (mo-di) twins account for 1 in 5 twin pregnancies.[16] Mo-di twins are at risk for several complications due to vascular anastomoses within the placenta; these complications are estimated to affect around 15% of mo-di twin pregnancies.[17]

Delivery planning is dependent on antenatal testing, fetal growth, and maternal comorbidities. Serial ultrasounds should be performed to assess for amniotic fluid volume and fetal growth starting at 16 weeks.[12] For uncomplicated mo-di twins, delivery can be planned between 34 0/7 and 37 6/7 weeks.[18] Mo-di twins with isolated fetal growth restriction should undergo delivery between 32 0/7 and 34 6/7 weeks.[18] Patients should receive 2 doses of antenatal corticosteroids within 7 days of delivery if delivery is planned before 34 weeks.[19] If the delivery plan is after 34 weeks, it is unclear if administering antenatal corticosteroids shows benefit in twin gestations. Although the ALPS trial demonstrated that administration of steroids in the late preterm period provided fetal benefit, there is no conclusive data that this benefit applies to multifetal gestations.[20]

Mo-di twins are candidates for a vaginal delivery if they meet the following criteria: the presenting twin is in the cephalic position, fetal growth discordance is <20%, and no contraindications to vaginal delivery are present. The Twin Birth Study demonstrated that the risks of neonatal morbidity and mortality in mo-di twins are no different in a vaginal delivery versus a planned cesarean section.[3]

Dichorionic Diamniotic Twins

Patients with uncomplicated dichorionic diamniotic (di-di) twin pregnancies should undergo weekly antenatal testing from 36 0/7 weeks until delivery. For patients with complications, surveillance may be considered earlier.[21] In uncomplicated di-di twins, delivery can be planned between 38 0/7 and 38 6/7 weeks.[18] For di-di twins with isolated fetal growth restriction, delivery is indicated between 36 0/7-37 6/7 weeks.[18] In a patient with di-di twins and either fetal growth restriction with abnormal uterine artery dopplers or maternal conditions such as preeclampsia, delivery is recommended between 34 0/7 and 36 6/7 weeks.[18] ACOG recommends vaginal delivery for di-di twins in patients without contraindications for vaginal delivery.[2]

Higher-Order Pregnancies

Triplet or higher-order pregnancies are rare.[22] There is no single protocol for antenatal testing for higher-order pregnancies; delivery timing and monitoring are individualized.[2] Delivery for triplets or higher-order pregnancies should be by cesarean section due to the increased risk of a cord accident.[2]

Personnel

A physician should be present for the vaginal delivery of a twin pregnancy due to the potential for conversion to cesarean section. A midwife may be present for the delivery of the twins if the patient desires. Additional support staff for both vaginal and cesarean deliveries include nursing staff for maternal care, a neonatologist to evaluate the twins, separate neonatal intensive care unit (NICU) teams for both neonates, surgical scrub technicians, anesthesiologists, and an anesthesia technician. Support and coaching personnel for the patient may also be present per hospital guidelines, including a family member or doula.

Preparation

A history and physical examination should be performed upon the patient's admission for delivery. Clinicians should know the patient's obstetric, medical, surgical, gynecologic, family, and social histories. There should be a discussion of the patient's birth plan, including a conversation regarding anesthesia, cord clamping, location of delivery, and who the patient desires to be present as their support person. A medication reconciliation should be performed, and any necessary medications should be continued on admission. The patient's allergies, as well as their reported reactions, must be documented.

Hospital consent forms should be reviewed with the patient, discussing the risks of vaginal delivery, cesarean section, and blood transfusion. Patients should be aware of the risks of vaginal delivery, including the possibility of breech extraction of the second twin and the indications and risks of operative vaginal delivery using forceps or vacuum assistance. The provider should discuss with the patient the indications for cesarean section, including both fetal and maternal indications. The risks of the cesarean section procedure should also be addressed. Finally, the provider should determine if the patient would be willing to receive a blood transfusion in the event of an emergency. The risks of blood transfusion, including adverse reactions and transmission of infectious diseases, should be discussed.

Intravenous (IV) access should be procured at least 1 site. Initial labs, including a type and screen and a complete blood count (CBC), should be collected. The patient's prenatal lab results should be reviewed, and penicillin should be initiated for Group B Strep prophylaxis if indicated. An ultrasound should be performed to confirm the presentation of the twins and to assess the amniotic fluid.

A postpartum hemorrhage kit should be available in the room before delivery. This kit should include misoprostol 200 mcg tablets, oxytocin 10 U, and methylergonovine 0.2 mg, and 15-methyl PGF 2α 0.25mg ampules. Access to an intrauterine balloon device, such as the Bakri balloon or the Jada device, should be secured.   

Before delivery, a time-out should be performed. This time-out should confirm the presentation of both fetuses and their estimated weights. Placentation should be confirmed. The plan for cord clamping should be confirmed with the NICU team (immediate versus delayed cord camping). The team should review any contraindications to uterotonics. For example, if the patient has a hypertensive disease of pregnancy, methylergonovine is not to be used; if the patient has asthma, 15-methyl PGF 2α should be avoided.[23]

Vaginal Delivery

A twin vaginal delivery should be performed in the operating room (OR). Once the patient's cervix is dilated to 10 centimeters, the delivery team should transport the patient to the OR with IV fluids running. The patient should be safely positioned in a comfortable way for her to push. In general, patients should be in a modified dorsal lithotomy position so the physician can access the vagina to assist in the delivery of the infants.

In the OR, 2 NICU teams should be available with resuscitation supplies for each neonate.

Cesarean Section

Before cesarean delivery, it is recommended that patients are fasting for at least 6 hours to reduce aspiration risk.[24] To reduce the risk of infection, patients receive IV antibiotics within 1 hour of the surgery's start time.[25] The recommended regimen is 1 g of Cefazolin for patients weighing <80 kg, 2 g of Cefazolin for patients between 80 kg and 120 kg, and 3 g for patients weighing ≥120 kg.[25] Clindamycin with an aminoglycoside can be administered for patients with anaphylactic reactions to penicillin or cephalosporins.[26] Additional dosing is indicated if the estimated blood loss is >1500 cc or the case lasts longer than 2 hours. The C-SOAP trial has demonstrated that in patients undergoing nonelective cesarean section, the administration of azithromycin can reduce the rate of postoperative infection.[27] In patients undergoing nonelective cesarean section, administration of azithromycin as well as a cephalosporin can be considered.

The patient is taken to the OR with IV fluids running. The anesthesia team ensures that the patient has adequate anesthesia coverage. The patient is placed in a supine position with a slight left tilt to relieve pressure on the inferior vena cava. A Foley catheter is placed. Abdominal skin preparation with an alcohol-based solution such as chlorhexidine should be performed.[28] Preoperative vaginal preparation has been adopted in some practices, with its primary benefit to reduce postoperative fever and endometritis in patients with ruptured membranes.[25][29] The patient is draped in the standard fashion.

Before the start of the procedure, the NICU team should be present in the OR. There should be separate NICU teams with supplies for each neonate.

Technique or Treatment

Vaginal Delivery                                                                                                                                                 

Once the patient has been appropriately positioned and her cervix found to be 10 cm dilated, the patient can begin the second stage of labor. As long as the fetal heart tracing continues to be reassuring and the patient continues to progress, the patient can continue to push.[30] During pushing, the fetal head goes through the 7 cardinal movements of labor: engagement, descent, flexion, internal rotation, extension, external rotation, and expulsion.[30] 

• Engagement is the passage of the fetal head to the level of the pelvic inlet.[30]                                                    
• Descent is the passage of the fetus through the pelvis.[30]                                                                          
• Flexion of the fetal head allows for the smallest diameter of the fetal head through the pelvis.[30]
• Internal rotation is the rotation of the fetal head to allow the widest portion of the head to pass through the pelvis.[30]
• Extension is when the fetal head is at the level of the introitus and the fetal head extends around the pubic symphysis.[30]
• External rotation, or restitution, is when the fetal head passively rotates to its correct anatomic position relative to the fetal torso.[30]
• Finally, expulsion is the delivery of the fetal head, followed by the anterior shoulder and the rest of the infant's body.[30] 

Following delivery, the cord should be clamped and cut, and the neonate should be passed to the waiting NICU team for evaluation.

Now, attention is turned to the second infant. An ultrasound is performed to assess the position of the second twin. If, on ultrasound, Twin B is found to be in the cephalic position, with the fetal head as the presenting part, the plan is to continue the labor process with artificial rupture of membranes of the second amniotic sac.[31] If twin B is engaged in the maternal pelvis, delivery of the second infant proceeds in the same fashion as the first.

If the ultrasound demonstrates that the second twin is in the breech or transverse position, maneuvers can be performed to proceed with breech delivery.[32] 

• The lower limbs of the second twin are identified.[31]                                                                              
• Both lower extremities are grasped, and the neonate should be engaged within the pelvis.[31]                                         
• At this point, it is appropriate to proceed with amniotomy.[31]                                                                        
• The neonate is spontaneously delivered to the scapula level, or the provider can place 1 hand on each hip with the thumbs on the sacrum to deliver the infant to the scapula level.[33]                                                      
• When the Pinard maneuver is performed, a blue towel will be placed on the back, and the neonate is gently rotated to the prone position with gentle traction if needed.[33]
• The Lovset maneuver can be performed to deliver the bilateral arms by rotating the infant's body 90° to allow for a sweep of the arm anteriorly.[33] 
• The birth of the fetal head can be accomplished by the Mauriceau-Smellie-Veit maneuver, which involves placing 1 hand on the occiput and using 2 fingers of the other hand to flex the maxilla and complete the delivery.[33]

Twin B's umbilical cord is clamped with 2 clamps to identify it. Cord blood and gases can be obtained. After the delivery of both neonates, attention is turned to the delivery of the placenta(s).[31] For more details on placental delivery, see StatPearls "Vaginal Delivery."[34] Any lacerations are identified and repaired.

Cesarean Delivery

The cesarean delivery of multiple gestations involves the same steps as a singleton procedure. There is no preferred skin incision type for cesarean delivery of a multifetal gestation. For details regarding choices of skin incision, refer to StatPearls "Cesarean Delivery" for more information.[35] A skin incision is made, and dissection is performed through the subcutaneous layer and fascia, followed by separation of the rectus muscles and entry into the peritoneum.[35] An assessment of the degree of dextrorotation of the uterus is performed to evaluate the safest incision site for the hysterotomy.[36] The decision for classical versus low transverse incision is provider-dependent based on the accessibility of the lower uterine segment as well as the gestational age of the neonates.[36]

In cases with 2 amniotic sacs, amniotomy is performed before the delivery of the infant, followed by clamping and cutting of the umbilical cords for both infants. At the time of delivery of the infant, umbilical cords are tagged in different ways so it is clear which cord belongs to which baby. In the case of infants that share an amniotic sac, amniotomy is performed, and the infants are delivered with clamping and cutting of the cord for both infants, ensuring the cords are tagged in a way that can differentiate the infants. If the neonate is in the cephalic position, the fetal head is brought to the level of the hysterotomy. With gentle fundal pressure, the neonate's anterior shoulder, followed by the posterior shoulder, is delivered through the hysterotomy, followed by the rest of the body. If the infant is found to be in the breech position, the same maneuvers performed during a vaginal delivery apply, including identifying the fetal feet and bringing them to the hysterotomy, the Pinard maneuver, the Lovset maneuver, and the Mauriceau-Smellie-Veit maneuver. 

Once the infants have been delivered, the placenta or placentas are delivered by gentle traction or manual extraction, depending on the type of multifetal gestation. Otherwise, the procedure is completed in the same fashion as a singleton delivery; see StatPearls "Cesarean Delivery" for details on the steps of the procedure.[35]

Complications

Multifetal gestations are associated with medical complications that can have significant impacts on maternal morbidity, including gestational diabetes, hypertensive disorders of pregnancy, and anemia.[2][37][38] Multifetal gestations are also associated with an increased risk of cesarean section and postpartum hemorrhage.[39] Management of these conditions follows the same guidelines as for singleton pregnancies.

There is no specified time limit between the delivery of twins A and B. However, a recent study states the median time to deliver the second twin is about 30 minutes.[40] When the time between delivery of the twins was >30 minutes, there was an increased risk of cesarean delivery.[40] This could be due to cord prolapse, non-reassuring fetal status, or an unengaged vertex of twin B.

After delivery of Twin A, there is the risk that the uterus may contract rapidly. If Twin B is breech or transverse, it may be difficult to perform necessary maneuvers due to uterine hypertonicity.[41][42] In this setting, a single dose of nitroglycerin 100 ug IV or a single dose of terbutaline 250 ug subcutaneously can be administered.[42] These medications can relax the uterus and allow for maneuvers to help facilitate delivery. If the maneuvers are still unable to be performed, the team should plan for cesarean delivery.[41]

If twin B is vertex and unengaged in the pelvis, the obstetrician should allow time for the fetal head to descend. Ultrasound should be performed to confirm there is no funic presentation or other malpresentation that would necessitate a cesarean section. There is no time limit between the delivery of the infants, so the decision to proceed with cesarean section is provider-dependent.[40]

Operative vaginal delivery may be required to complete the delivery of the second twin. Indications for an operative vaginal delivery are a prolonged second stage of labor, suspicion of fetal compromise, or maternal benefit.[43] A patient is a candidate for an operative vaginal delivery given an assessment of the following: the cervix is fully dilated, membranes have been ruptured, the bladder has been emptied, an estimated fetal weight is reviewed, the maternal pelvis is deemed adequate, fetal station and fetal head position are evaluated, and adequate anesthesia is confirmed.[43] If the fetal head is not engaged in the pelvis or if the head position cannot be determined, an operative vaginal delivery is contraindicated.[43] Operative vaginal delivery is performed with either forceps or a vacuum device.

There are different forceps devices used based on the specific circumstance; these include the following:

• Piper forceps are used for breech delivery. They have long curved blades with a perineal curve to mimic the birth canal and a long shaft that allows optimal access.[44]
• Simpson forceps are useful to assist in delivery when the fetal head is within the birth canal. Simpson forceps have long-fenestrated blades that are useful in delivering a baby with significant molding. These forceps have parallel shanks and an English lock.[45]                                                                                                                  
• Wrigley forceps are also useful to assist in delivery when the fetal head is within the birth canal. Wrigley forceps have a similar fenestrated blade with an English lock, but they have much shorter handles and can be used in cesarean delivery as well as vaginal delivery when the fetal head is near the introitus.[46]
• Luikart forceps are used to rotate the fetal head when it is in the asynclitic position. Luikart forceps have pseudo-fenestrated blades, overlapping shanks, a sliding lock, and tongue-in-groove handles.[47]                       
• Kielland forceps help rotate the fetal head from the occiput posterior to the occiput anterior position. Keilland forceps are fenestrated with minimal pelvic curvature and a sliding lock and are more lightweight.[48] 

A trained, experienced provider should perform operative vaginal delivery with forceps. 

During the breech delivery of the second twin, there is the risk of head entrapment, which is an obstetric emergency. Head entrapment is more common during a preterm delivery when the cervix is incompletely dilated.[49] Piper forceps can be used to deliver the head, but if this fails, the physician must then begin performing maneuvers to assist in the delivery of the fetal head, such as the Mauriceau-Smellie-Veit maneuver, rotation of the fetus to the transverse position, McRoberts maneuver (flexing the maternal legs toward her abdomen), and suprapubic pressure.[49] To increase the relaxation of the uterus, the obstetrician may administer terbutaline or nitroglycerine.[50] If all attempts are unsuccessful or if there is evidence of fetal distress, the obstetrician can place Duhrssen's incisions.[51] These incisions are made at 10 o'clock and 2 o'clock on the cervix to avoid the cervical neurovascular bundles at 3 o'clock and 9 o'clock and to avoid damage to the bladder at 12 o'clock or the rectum at 6 o'clock.[51]

Clinical Significance

Multifetal gestations are on the rise with increases in assisted reproductive technology and are associated with increased maternal risks as well as increased rates of complications for neonates.[2] The greatest fetal risk of multifetal delivery is prematurity.[2] Maternal risks during delivery can have devastating outcomes, such as postpartum hemorrhage, preeclampsia, and even death.[2] Although some patients are candidates for a vaginal delivery, there are still risks, including the need for operative vaginal delivery, fetal head entrapment, or the need for cesarean section.

Understanding the risks and benefits of vaginal delivery versus cesarean section for multifetal gestations can help patients make the best decisions for their pregnancy. A clear understanding of evidence-based medicine can help physicians provide the best outcomes. Before delivery, the healthcare team should discuss the plan for delivery with the patient, including the criteria for safe vaginal delivery, the risks associated with a delivery of twins, risks associated with a vaginal delivery, and the risks associated with a cesarean section.

Enhancing Healthcare Team Outcomes

An outpatient team that includes an obstetrician or nurse midwife, maternal-fetal medicine physician, and a sonographer will be involved in the patient's prenatal care and delivery planning before the patient's arrival on labor and delivery. The patient should be counseled regarding signs of preterm labor to ensure she promptly presents to labor and delivery. A growth ultrasound should be performed within 1 week of delivery to estimate fetal weight and determine if significant growth discordance exists. The maternal-fetal medicine specialist will determine the timing of delivery based on the type of multifetal gestation and an evaluation of any fetal and maternal complications. Before admission to labor and delivery, the patient will develop her birth plan with her obstetrician and determine which support people she would like to have involved in her care.

On arrival to labor and delivery, the patient will meet her multidisciplinary team, including labor and delivery nurses, obstetricians (as well as a midwife if desired), maternal-fetal medicine specialists, anesthesiologists, neonatologists, pediatricians, advanced care practitioners, and surgical scrub technicians. The team will review the patient's last ultrasound and most recent labs. The obstetrician will perform an ultrasound on arrival to confirm the presentation of fetuses. Depending on the hospital, nursing staff or phlebotomists will collect baseline labs. The obstetrician and anesthesia team will obtain the required consent forms and counsel the patient on complications. Additional team members, including a surgical scrub technician, extra nursing staff, a neonatologist, and the NICU team, will be present during the delivery procedure.

Communication between medical professionals is critical for a successful and safe delivery. Executing a multiple birth delivery is a multidisciplinary team effort. From arrival on the labor and delivery floor to discharge from the postpartum unit, multiple interprofessional teams ensure a safe delivery and postpartum course. This collective effort aims to elevate patient-centered care, improve outcomes, enhance patient safety, and optimize team performance.

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Disclosure: Emily Root declares no relevant financial relationships with ineligible companies.

Disclosure: Tiffany Tonismae declares no relevant financial relationships with ineligible companies.