The incidence of spontaneous abortion of at least one of several fetuses is increased in multiple pregnancy. Stillbirth occurs twice as often among twins as among singleton pregnancies. Premature labor and delivery as well as premature rupture of the membranes are also greatly increased. The average gestational age at delivery is 36-37 weeks for twins, 33 weeks for triplets, and 31 weeks for quadruplets. Efforts to reduce the incidence of prematurity have thus far been unsuccessful.
Placenta previa may be responsible for antepartum bleeding, malpresentation, or unengagement of the first fetus. A large placenta (or placentas) and possibly fundal scarring or tumor may lead to low implantation of the placenta.
Premature separation of the placenta may occur antepartum, perhaps in association with preeclampsia-eclampsia or with rupture of membranes of twin A and the initiation of strong uterine contractions, or after the delivery of the first twin. Careless traction on the first cord may encourage early partial separation of the placenta.
Hypochromic normocytic anemia is 2-3 times more common in multiple pregnancy than in singleton pregnancy. Urinary tract infection is at least twice as frequent in multiple pregnancy as in singleton pregnancy due to increased ureteral dilatation secondary to higher serum progesterone and uterine pressure on the ureters. Preeclampsia-eclampsia occurs about 3 times more often in multiple pregnancy than in a singleton pregnancy.
A thinned uterine wall, secondary to unusually large uterine contents, is associated with hypotonic uterine contractions and a longer latent stage of labor. However, prolonged labor is uncommon in multiple pregnancy because rupture of the membranes generally is followed by improvements in the uterine contraction pattern. Uterine atony often is accompanied by excessive loss of blood postpartum owing to inability of the overdistended uterus to contract well and remain contracted after delivery.
If the amniotic sac of the second twin ruptures before that of the first and if the cord prolapses, cesarean section usually is indicated.
When there are 2 separate placentas, one of them may deliver immediately after the first twin. Although the second twin may not be compromised, it is best to proceed with its delivery, both for its protection and to conserve maternal blood.
Operative intervention is more likely in multiple pregnancy because of increased obstetric problems such as malpresentation, prolapsed cord, and fetal distress.
Fetal death is about 3 times more common in multiple pregnancy than in singleton pregnancy. Death may be due to developmental anomalies, cord compression, or placental disorders. The greatest hazard from cord compression is cord entanglement of monozygotic twins with only one amniotic sac. Developmental anomalies and polyhydramnios are common in monozygotic twins.
Almost twice as many monozygotic as dizygotic twins die in the perinatal period. Attrition is even greater for triplets, quadruplets, and higher order pregnancies. Even so, preterm delivery and intrapartum complications are the most common causes of fetal loss in multiple pregnancy. All too frequently preterm delivery is occasioned by premature rupture of the membranes, which occurs in about 25% of twin, 50% of triplet, and 75% of quadruplet pregnancies.
Abnormal and breech presentation, circulatory interference by one fetus with the other, and operative delivery all increase fetal loss. Prolapse of the cord occurs 5 times more often in multiple than in singleton pregnancy. Premature separation of the placenta before delivery of the second twin may cause death of the second twin by hypoxia.
Neonatal outcome is very much dependent on gestational age at delivery. In general, morbidity and mortality rates are similar for twins and singletons of equivalent gestational ages. Many outcome data are stratified according to birthweight. Therefore, the slowing of growth in the third trimester can give twin fetuses the advantage of increased gestational age for weight. Advances in neonatal intensive care have made survival possible even at 23 weeks’ gestation, although usually with considerable morbidity, including but not limited to intraventricular hemorrhage, chronic lung disease, and necrotizing enterocolitis. Because intact survival is much more likely after 34 weeks, it is desirable to prolong gestation at least to this point when possible. The adage “one day in utero saves two days in intensive care” applies to the economic as well as the emotional costs of caring for premature infants.
It is imperative that an experienced physician be present for resuscitation and stabilization of each infant born premature. Antenatal diagnosis of multiple gestation facilitates delivery at an appropriate center. Delivery before the 36th week is twice as frequent in twin pregnancies as in singleton pregnancies. Intracranial injury is more common in premature infants, even those delivered spontaneously. An increased risk of cerebral palsy is found in twins, especially very low-birthweight babies, and also in liveborn co-twins of fetuses who died in utero.
Treatment of twin-to-twin transfusion syndrome in utero remains experimental. After delivery, therapy includes replacing blood in the donor twin to correct fluid and electrolyte imbalance. In the recipient twin, phlebotomy is necessary until normal venous pressure is restored. Often, other therapy for cardiac failure (eg, digitalis) is necessary.
Revision date: June 20, 2011
Last revised: by Jorge P. Ribeiro, MD