**5.1. Fetus presentation**

**2. Risk of fetal death in the third trimester for twin pregnancies**

imbalance in placental anastomoses, may be overloaded in the third trimester [4].

surveillance after 34 weeks of gestation in multiple pregnancies [6].

**3. Time of delivery in dichorionic pregnancies**

**4. Time of delivery in monochorionic pregnancies**

insufficiency [1].

212 Multiple Pregnancy - New Challenges

for MC.

mended before 38 weeks.

Multiple pregnancies have high rates of mortality and morbidity when compared to single pregnancies. This is mainly due to prematurity, complications close to delivery, and placental

In fact, this risk is related to chorionicity. The monochorionic (MC) pregnancies present a higher incidence of perinatal mortality, higher admission in neonatal intensive care unit and low birth weight [3]. It is possible that the single placental mass shared between pairs originates from an

A large Dutch cohort with 1407 multiple pregnancies showed that after 32 weeks' gestation, mortality was 11.6% in MC and 5% in dichorionic (DC) [5]. The risk of uterine death was significantly higher in MC than in DC (hazard ratio 8.8, 95% CI 2.7–28.9), and in most cases no change in fetal status was observed. The authors concluded that fetal vitality control was not sufficient to prevent adverse events and delivery should be planned up to the 37th week

A study with 94,170 multiple deliveries showed that the risk of fetal death increased significantly between 37 and 38 weeks of gestation in twin pregnancies. This risk was higher between 34 and 37 weeks of gestation in triplet pregnancies. The risk of child death after delivery gradually declined as pregnancies neared full term. This group recommended increased fetal

The American College of Obstetricians and Gynecologists (ACOG) suggests that delivery be performed between 38 + 0 and 38 + 6 weeks in uncomplicated twin dichorionic pregnancies [7]. Depending on complications such as fetal growth restriction, termination of pregnancy is recom-

In 2016, a systematic review included 32 studies (29,685 dichorionic, 5486 monochorionic pregnancies) and showed that in dichorionic pregnancies beyond 34 weeks (15 studies, 17,830 pregnancies), the weekly risk of stillbirths due to expectant management and the risk of neonatal death were balanced at the 37th week of gestation. When delivery was delayed for 1 week (up to 38 weeks) led to an additional 8.8 perinatal deaths per 1000 pregnancies [8].

The same review showed that monochorionic pregnancies beyond 34 weeks (13 studies, 2149 pregnancies), had a tendency for an increase in stillbirths compared to neonatal deaths after 36 weeks, with an additional 2.5 per 1000 perinatal deaths, which was not significant [8].

Determining fetal presentation is fundamental in the decision of the mode of delivery. The presentation of twin pairs in a term twin pregnancy is 40% of the times cephalic/cephalic, 35–40% cephalic/non-cephalic and only 20% with the first twin non-cephalic [15]. It is a general consensus that, when both fetuses are in cephalic presentation, a vaginal delivery should be attempted [13–15]. However, it is important to notice that the second twin change its presentation in about 20% of the time, after the first one is born [15].

When the second twin is in a non-cephalic presentation, vaginal delivery is controversial. Some studies say that neonatal morbidity is higher for the second twin in those cases and an elective cesarean section should be planned [16, 17]. However, both a systematic review and meta-analysis [14] and a recent published prospective cohort study [18] support that cesarean deliveries neither add neonatal morbidity nor mortality. Therefore, a vaginal delivery is a safe option. In those cases, the second twin can either be delivered by breech extraction or an external cephalic version can be attempted [19].

In general, the accuracy of estimation weight in twin pregnancies is worse than single pregnancies. Biometric measurement of these fetuses in the third trimester is greatly impaired due to the technical difficulty of examination. When using 33 formulas to assess the accuracy of estimation weight by two-dimensional ultrasonography, 25 of these formulas present a weight variation of less than 10% for single pregnancies, but only 3 of these formulas present

Time and Mode of Delivery in Twin Pregnancies http://dx.doi.org/10.5772/intechopen.80092 215

An ongoing study that has been developed in multiple pregnancy unit of Federal University of São Paulo has shown that the use of fraction limb volume in twin pregnancies can improve the accuracy of estimation weight in these pregnancies, as well as reduce the time of the examination. Although evaluation of fetal body volume through the use of magnetic resonance imaging is still considered an expensive method, there is good accuracy in fetal weight estimation, besides being a good predictor in the diagnoses of small fetuses for gestational age when

Estimating weight in twin pregnancies remains a challenge. New research needs to be con-

Fetal weight should not be considered when both fetuses are cephalic. In those cases, regardless the fetal weight, a vaginal delivery can be attempted. However, in cephalic/non-cephalic twin pregnancies, the influence of weight on mode of delivery is controversial. Most studies showed worst perinatal outcomes for vaginal deliveries when the second twin was non-

Weight difference is related to worst neonatal outcomes, regardless the delivery mode [31], and also to unsuccessful attempt of labor [32]. Furthermore, a weight difference above 40% has been associated with higher neonatal mortality rates in vaginal deliveries, regardless fetal

A previous cesarean delivery is considered a risk factor for an emergency C-section after attempting a vaginal delivery in twin pregnancies [34]. Regardless, a caution trial of labor can

On the other hand, patients with two or more previous cesarean sections should not attempt

There is limited existing evidence to determine the safest mode of delivery for extremely preterm twins. Therefore, it is important to consider the fetal presentation and weight when

A recently published meta-analysis showed no significant difference in neonatal death and severe brain injury by mode of delivery for cephalic/non-cephalic twins with a gestational age under 28 weeks [36]. This study found higher rates of maternal complications in growth-discordant twins.

the same result for twin pregnancies [27].

cephalic and under 1500 g [29, 30].

**5.3. Previous C-section**

**5.4. Preterm pairs**

compared to two-dimensional ultrasonography [28].

presentation, in a retrospective study in 2005 [33].

a vaginal delivery due to higher risk of uterine rupture.

deciding the delivery mode, regardless gestational age.

ducted in search for new methods in order to improve accuracy.

be a safe option in those patients, when the first twin is cephalic [35].

Finally, when the first twin is non-cephalic, the safest delivery mode is the cesarean section. A randomized multicenter trial, The Breech Trial, showed that a planned cesarean delivery decreases significantly perinatal mortality and neonatal serious morbidity, when compared with a planned vaginal delivery in pregnancies with a non-cephalic presenting twin [20].
