Perinatal mortality and morbidity rates among singleton,twin, and triplet gestations

Objective: To determine rates of perinatal mortality and morbidity from 24 to 43 weeks gestation among singletons, twins, and triplets.Methods: Successfully linked data from 1992 Californian maternal and infant discharge records as well as birth and death certificates from acute care civilian hospitals were examined for perinatal mortality and morbidity. Perinatal mortality was defined as the sum of all stillbirths and neonatal deaths. Deliveries from 24 to 43 weeks gestation among singleton, twin, and triplet pregnancies were collected as separate data sets. Perinatal mortality was identified using birth certificate death indicators excluding deaths caused by congenital anomalies. Neonatal deaths were identified from death indicators found in the death certificates. For the purpose of this study, perinatal morbidities were identified by ICD-9 codes and limited to respiratory distress syndrome (RDS), intraventricular hemorrhage (IVH), and necrotizing enterocolitis (NEC). Perinatal mortality and morbidity rates were expressed as a percent of live births stratified by gestational age. Perinatal mortality data were expressed in log scale and perinatal morbidity rates were statistically compared.Results: There were 571,390 total births in California of which 527,677 (92%) were singleton, 12,535 (2%) were twin, and 367 (0.06%) were triplet gestations. Across gestation, the rate of RDS between triplets and twins was comparable (6.6% vs 6.8%). However, the rates of IVH and NEC were significantly greater in triplets than in twins (20% vs 8%, P < .0001, and 25% vs 9%, P < .0001, respectively). The perinatal mortality rates are shown below.

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Conclusions: Perinatal mortality rates were comparable among singleton, twin, and triplet gestations delivered between 24 and 30 weeks gestation. Unlike singletons and twins, the triplet perinatal mortality rate did not fall between 31 and 36 weeks gestation and remained at 2.6%. Twin perinatal mortality rate was equivalent to singletons until 36 weeks gestation. IVH and NEC were significantly greater among triplets regardless of gestational age. These data suggest that antepartum fetal surveillance of triplet pregnancies should start as early as 30 weeks gestation while testing for twin pregnancies can begin at 36 weeks gestation.     

Is peripartum hysterectomy more common in multiple gestations?

OBJECTIVE: To compare the occurrence of peripartum hysterectomy between singleton and multiple gestations. METHODS: This was a historical cohort study comparing the occurrence of peripartum hysterectomy between singleton and multiple gestations at Banner Good Samaritan Regional Medical Center, Phoenix, Arizona, from January 1, 1996, to December 31, 2001. RESULTS: During the study years, 42,595 singleton, 1,131 twin, 164 triplet, 35 quadruplet, and 2 quintuplet deliveries occurred. A total of 100 peripartum hysterectomies were performed. Of these hysterectomies, 88 occurred in singletons, 5 in twins, 6 in triplets, and 1 in quadruplets. The overall occurrence of peripartum hysterectomy was 2.28 per 1,000, and the occurrence of emergent peripartum hysterectomy was 1.73 per 1,000. Multiple gestations had a significantly greater risk of emergent peripartum hysterectomy than singletons (odds ratio [OR] 6.04, 95% confidence interval [CI] 3.28-11.11; P < .001). This difference was more pronounced among higher-order multiple gestations: twins (OR 2.95, 95% CI 1.22-7.13, P = .03), triplets (OR 25.22, 95% CI 11.02-57.77, P < .001), and quadruplets (OR 19.53, 95% CI 3.34-114.69, P = .04). When compared with singletons, higher-order multiple gestations had nearly a 24-fold increased risk of emergent peripartum hysterectomy (OR 23.97, 95% CI 11.05-51.99, P < .001). CONCLUSION: Multiple gestations have a significantly higher occurrence of emergent peripartum hysterectomy than singletons. This information should be used in counseling and managing patients with these pregnancies.     

Pregnancy outcome of early multifetal pregnancy reduction: triplets to twins versus triplets to singletons

Multifetal pregnancy reduction (MPR) of triplets to twins results in improved pregnancy outcomes compared with triplet gestations managed expectantly. Perinatal outcomes of early transvaginal MPR from triplets to twins were compared with reduction from triplets to singletons. Seventy-four trichorionic triplet pregnancies that underwent early transvaginal MPR at 6–8 weeks gestation were included. Cases were divided into two groups according to the initial procedure: reduction to twin (n = 55) or to singleton (n = 19) gestations. Infants from triplet pregnancies reduced to twins were delivered earlier (36.6 versus 37.9 weeks; P = 0.04) and had lower mean birth weights (2364 g versus 2748 g; P = 0.02) compared with those from triplets reduced to singleton gestations. The rates of pregnancy loss before 24 weeks (3.6% versus 5.3%), as well as of preterm delivery before 32 and 34 weeks of gestation (0% versus 5.3% and 7.3% versus 5.3%, respectively) were similar between the twin and singleton pregnancies. No significant difference was found in the prevalence of gestational diabetes (15.1% versus 5.6%) or gestational hypertension (24.5% versus 16.7%) between the groups. Selective reduction of triplet pregnancies to singleton rather than twin gestations is associated with improved outcomes.     

The Principal Pregnancy Complications Resulting in Preterm Birth in Singleton and Twin Gestations

Preterm birth is the major cause of perinatal mortality for both singleton and twin gestations in the United States; most preterm birth prevention programs are primarily structured to detect and treat preterm labor. Most of these programs have had limited success, and the preterm birth rate for twins has remained well above that for singletons. Little attention has been paid to the question of whether the frequency of conditions that result in preterm twin delivery differs from those that result in the delivery of preterm singletons. Delivery records were reviewed for all 1,976 preterm (24–36 completed gestational weeks) singleton pregnancies and 221 preterm twin pregnancies delivered at the University of Connecticut Health Center, 1980–1989, to determine the primary complication that resulted in preterm delivery. Premature rupture of membranes was responsible for 46% of these singleton preterm deliveries, while the other causes were preterm labor with intact membranes (20%), pregnancy-induced hypertension (15%), antepartum hemorrhage (9%), and other maternal-fetal indications (10%). The five groups differed significantly in maternal and neonatal characteristics. The principal pregnancy complications resulting in preterm delivery of twins were preterm rupture of membranes (42%), preterm labor (31%), antepartum hemorrhage (4%), pregnancy-induced hypertension (11%), and other maternal-fetal indications (12%). Compared to preterm singletons, the preterm twins were significantly more likely to deliver because of preterm labor and less likely to deliver because of hemorrhage. Substantial reduction in the preterm birth rate requires programs tailored to the specific population and etiologies involved and should not solely address preterm labor.     

Effect of prolongation of pregnancy on perinatal mortality

Objectives: (1) To determine the distribution of singleton and twin births according to gestational age in a Nigerian obstetric population; and (2) to compare their perinatal outcomes according to gestational age. Methods: A 10-year retrospective comparative study of twin and singleton births at a tertiary care center in Enugu, Nigeria. The variables analyzed were: the proportion of deliveries occurring at each gestational age, the gestational age-specific rates for stillbirths, cesarean section, babies with 1-min Apgar scores less than 4 and those whose birthweights were below the 10th percentile for gestational age. The trends in these rates were determined by finding the best fitting polynomial regression curve for each variable. Tests of statistical significance for trends in proportions were carried out by means of the χ²-test at the 95% confidence level. Results: Of the 496 twin births, 3.6% compared with 17.3% of the 496 singleton births went beyond 40 weeks’ gestation while 1.2% of the twin and 4.4% of the singleton deliveries occurred at 42 weeks’ gestation or beyond. For twins as well as singletons, there was a consistent and significant decline in the stillbirth rate and the proportion of babies with 1-min Apgar scores less than 4 up to 42 weeks (P=0.0000). Among the twins, the proportion of babies with birthweights below the 10th percentile (i.e. those with impaired growth) significantly rose from 28 weeks and above (P=0.0000) while among the singletons, a declining trend with gestational age was observed (P=0.0003). However, among the twins with impaired growth, the stillbirth rate neither differed between the first and second twins at each gestational age nor did it increase with gestational age in both the first and second twins. While the cesarean section rate for singletons remained almost stable at approximately 13%, there was a significant rise in the cesarean section rate with gestational age among the twin births. Conclusions: There were 1.2% of twin deliveries compared with 4.4% of singleton deliveries which occurred at 42 weeks’ gestation or beyond. In the Nigerian population studied, the perinatal outcomes in twins did not differ from those of singletons up to 42 weeks’ gestation suggesting that the 42-week cut-off for prolonged pregnancy applies equally well to twins as to singletons.     

The Outcome of Twin Pregnancies in Dunedin 1968–1978

Summary: Of 14,473 pregnancies in Dunedin City between 1968 and 1978, 1.07% were twin (1 in 93.4 pregnancies). Perinatal mortality has decreased over this period for both twins and singletons. To examine the hypothesis that the tendency for twins to be preterm and small for gestational age explained their increased mortality and morbidity, groups of twins and singletons of like birth-weight and gestational age were compared. No significant differences were found, suggesting that birth-weight and gestational age are the major determinants of outcome, and that a twin should fare no worse than a singleton of similar birth-weight and gestational age.     

Epidemiology of twinning in developed countries

Twin births contribute disproportionately to the overall burden of perinatal morbidity and mortality in developed countries. Twins constitute 2%-4% of all births, and the rate of twining has increased by 76% between 1980 and 2009. The rate of preterm birth (<37 weeks) among twins is about 60%. Of all twin preterm births in the United States, roughly half are indicated, a third are due to spontaneous onset of labor, and about 10% are due to preterm premature rupture of membranes. Mortality related to preterm birth is influenced by antecedent factors and is highest when preterm delivery is the consequence of preterm premature rupture of membranes, followed by those as a result of spontaneous preterm labor and lowest among indicated preterm births. There also appears to have been a recent decline in serious neonatal morbidity (one or more of 5-minute Apgar score <4, neonatal seizures or assisted ventilation for ≥ 30 minutes) among twin gestations. Compared with twins conceived naturally, those born of assisted reproduction methods are more likely to deliver at <37 weeks. Although perinatal mortality rates have declined among twin births, the effect of preterm delivery on trends in mortality and morbidity and other long-term consequences remain issues for major concern. With the rapid increase in the liberal use of assisted reproduction methods combined with women electing to postpone their pregnancies and increased likelihood of spontaneous twins with advancing maternal age, this review underscores the need to develop priorities to understand the peripartum and long-term consequences facing twin births.     

Twin versus singleton pregnancies complicated by preterm premature rupture of membranes

Objective: To compare latency period, infectious morbidity, neonatal morbidity and neonatal mortality in twin versus singleton pregnancies complicated by preterm premature rupture of membranes (PPROM) remote from term. Methods: A retrospective, matched cohort study comparing 41 twin and 82 singleton pregnancies complicated by PPROM between 24-0/7 and 31-6/7 weeks’ gestation. The data were obtained by reviewing maternal and neonatal charts. Results: The median latency periods were 3.6 days (interquartile range 1.5–13.9 days) for twins and 6.2 days (interquartile range 2.9–11.8 days) for singletons (p?=?0.86). Twins were less likely to be complicated by clinical chorioamnionitis when compared with singletons (4/41 [9.8%] vs. 19/82 [23.2%], relative risk [RR] 0.42, 95% confidence interval [CI] 0.18–0.96). Histological evidence of chorioamnionitis was also lower in twins compared with singletons (14/39 [35.9%] vs. 46/68 [67.7%], RR 0.56, 95% CI, 0.34–0.92). These differences persisted after adjusting for race, insurance status, latency period and route of delivery. Neonatal morbidity and mortality rates were similar between the two groups. Conclusions: There was not a statistically significant difference in the latency periods for twin and singleton pregnancies complicated by PPROM. Clinical chorioamnionitis and histological evidence of infection were significantly less common in twins compared with singletons.     

The origins and outcomes of triplet and quadruplet pregnancies in Nova Scotia: 1980 to 2001

The objective of this study was to determine the rate, origin, maternal and perinatal outcomes, and the associated hospital costs of higher order multiple births in one Canadian province. All higher order multiple pregnancies (triplets and above) in Nova Scotia over a 22-year period (1980 to 2001) were reviewed, and the maternal and perinatal outcomes and hospital costs were compared with singletons and twins in the same hospital population. During the 22-year period, 116,785 infants were delivered, including 3448 twins, 99 triplets, and 16 quadruplets. Of the higher order multiple gestations, 51.4% were conceived through infertility therapy. When compared with mothers of either singletons or twins, mothers of higher order gestations were significantly older, had longer antepartum and postpartum hospital stays, were more likely to have cesarean delivery, preterm labor, preeclampsia, and require intensive care unit admission. Triplets and quadruplets had significantly higher rates of preterm delivery, major anomalies, neonatal intensive care, respiratory distress syndrome, intrauterine growth restriction, serious morbidity, 5-minute Apgar scores < or = 3, and neonatal death than twins or singletons. The estimated hospital costs for this population ranged from 6,750 US dollars for a singleton pregnancy to 278,400 US dollars for a quadruplet pregnancy. Maternal morbidity, perinatal morbidity and mortality, and hospital costs are significantly increased in higher order births compared with both twins and singletons.     

Morbidity and mortality of preterm twins and higher-order multiple births.

OBJECTIVE: To determine if preterm infants of higher-order multiple (HOM) gestations have a significantly worse outcome during hospital stay when compared with preterm twins. STUDY DESIGN: Retrospective cohort analysis. METHODS: Perinatal outcome variables including gestational age (GA), birthweight, prenatal steroid use, cesarean section delivery rate, Apgar scores, and growth retardation were analyzed for 106 preterm HOM births (triplets and quadruplets) versus 328 preterm twins admitted to a single tertiary level neonatal intensive care unit. A comparison of the mortality and major neonatal morbidities such as respiratory distress syndrome, patent ductus arteriosus, intraventricular hemorrhage, necrotizing enterocolitis, bronchopulmonary dysplasia, and retinopathy of prematurity was made for these two groups. In addition, the duration of respiratory support including surfactant therapy, nasal continuous positive airway pressure, and mechanical ventilation, as well as the length of hospitalization, was analyzed. RESULTS: There were no significant differences in major morbidities between the infants of HOM and twin births of similar GA. There was no statistically significant difference in mortality, but the data showed a trend for lesser mortality in HOM. There was a highly significant increase in antenatal steroid use as well as the use of cesarean section for delivery in the HOM when compared with twin gestations. The infants of HOM gestations were of significantly lower birthweight than the twins and had a longer hospitalization. CONCLUSION: Although premature infants of HOM had lower birthweight and needed a longer hospital stay, their mortality and morbidity at hospital discharge were not worse than that for preterm twins.     

Perinatal mortality in twin pregnancy: an analysis of birth weight-specific mortality rates and adjusted mortality rates for birth weight distributions

The objective of this study is to compare the fetal mortality rate (FMR), early neonatal mortality rate (ENMR) and perinatal mortality rate (PMR) of twin and single births. It is based on a survey which was carried out in 22 Hospital Centers in Spain in 1980, and covered 1,956 twins born and 110,734 singletons born. The FMR in twins was 36.3/1000 and 8.8/1000 for singletons. The ENMR in twins was 36.1/1000 and 5.7/1000 for singletons. The PMR in twins was 71.1/1000 and 14.4/1000 for singletons. When birthweight-specific PMR in twin and singletons births are compared, there were no differences between the rates for groups 500-999 g and 1000-1499 g. For birthweight groups of 1500-1999 g (124.4 vs 283.8/1000) and 2000-2999 g (29.6 vs 73.2/1000) the rates for twins were about twice lower than those for single births. The PMR for 2500 g and over birthweight was about twice higher in twins than in singletons (12.5 vs 5.5/1000). After we adjusted for birthweight there was a difference in the FMR (12.6 vs 9.8/1000) and the PMR (19.1 vs 16.0/1000, and no difference in the ENMR between twins and singletons (5.9 vs 6.4/1000), indicating that most of the differences among crude rates are due to differences in distribution of birthweight.     

Twin vs. singleton pregnancy. Clinical characteristics and latency periods in preterm premature rupture of membranes.

OBJECTIVE: To compare the clinical characteristics and latency periods (latencies) of preterm premature rupture of the membranes (PPROM) in twin vs. singleton pregnancy. STUDY DESIGN: Between January 1986 and December 1996, data on all women with singleton and twin gestations complicated by PPROM were reviewed. Perinatal morbidity, mortality and latencies between singleton and twin pregnancies were compared. A further division according to PPROM at < 30 and > or = 30 weeks' gestation was made in both groups. Their latencies were compared. RESULTS: A total of 131 singleton and 48 twin pregnancies with PPROM between 20 and 36 weeks' gestation were included in this series. Regardless of the gestational age at PPROM, the mean latencies of singleton and twin pregnancies were statistically similar (4.4 +/- 3.3 vs. 3.4 +/- 2.9 days, nonsignificant). When PPROM occurred at > or = 30 weeks, the latency of twin pregnancies was shorter than that of singleton pregnancies (2.5 +/- 1.9 vs. 3.7 +/- 2.6 days, P < .05). In both groups, the latencies of PPROM at < 30 weeks were longer than that at > or = 30 weeks (singleton, 5.6 +/- 4.0 vs. 3.7 +/- 2.6 days, P < .005; twin, 4.8 +/- 3.5 vs. 2.5 +/- 1.9 days, P < .05). We also observed a higher percentage of deliveries within the initial 48 hours in twin pregnancies: 50% of women delivered within 48 hours after PPROM and 91.7% within 7 days. In contrast, 26.7% and 85.5% of singleton pregnancies with PPROM were delivered within 48 hours and 7 days, respectively. Perinatal and neonatal outcomes in both groups were similar. CONCLUSION: This investigation provides the basis for patient counseling and management in twin pregnancies with PPROM. In general, singleton and twin pregnancies with PPROM had similar latencies. Latency in PPROM at < 30 was longer than that of PPROM at > or = 30 weeks' gestation in both singleton and twin pregnancies. When PPROM occurred at < 30 weeks' gestation, both groups appeared to have similar latencies. In pregnancies with PPROM at > or = 30 weeks' gestation, latency in twins was shorter than in singleton pregnancies. In twin pregnancies with PPROM after 30 weeks' gestation, prompt steroid administration for fetal lung maturity should be considered.     

Accuracy of fetal fibronectin to predict preterm birth in twin gestations with symptoms of labor

OBJECTIVE: To investigate accuracy of fetal fibronectin testing to predict preterm birth in twin gestations with symptoms of preterm labor. METHODS: We reviewed charts of all patients with twin gestations who underwent fetal fibronectin testing and presented with complaints of preterm labor between January 1, 2000, and June 30, 2004. We also reviewed the charts of all singleton gestations with similar complaints that had fetal fibronectin testing between January 1, 2000, and December 31, 2001. All samples were processed using a rapid fetal fibronectin detection system. We calculated the sensitivity, specificity, positive predictive value, and negative predictive value of fetal fibronectin testing in singleton and twin gestations in predicting delivery within 14 days of testing. RESULTS: Four hundred twenty-nine singletons and 87 twins met the inclusion criteria. The birth rate before 34 weeks of gestation for singletons was 3.5% compared with the rate of twin pregnancies of 28.7%. Fetal fibronectin predicted delivery within 14 days of testing with a sensitivity, specificity, and positive and negative predictive values in singleton gestations of 82%, 90%, 17%, and 99%, respectively. In twin gestations, fetal fibronectin predicted delivery within 14 days of testing with a sensitivity, specificity, and positive and negative predictive values of 71%, 74%, 19%, and 97%, respectively. CONCLUSION: As noted in singleton pregnancies, fetal fibronectin testing in twins has a high negative predictive value. Fetal fibronectin evaluation may be a useful tool in screening twins with symptoms of preterm labor, because a negative result places these women at a low risk for delivering within 2 weeks of testing.     

Contribution of Gestational Age and Birth Weight to Perinatal Viability in Singletons Versus Twins

The objective of this study was to determine the effects of birth weight and gestational age on twin vs. singleton mortality. Population-based analysis of live births, fetal deaths, and infant deaths by plurality in the United States from 1983 to 1986 was conducted. Seven mortality rates and relative risks (RRs) of twin vs. singleton mortality were calculated by birth weight, gestational age, and combined birth weight and gestational age. The mortality rates included fetal, perinatal, early neonatal, late neonatal, neonatal, postneonatal, and infant. Twins had 3–4 times the RRs of mortality compared to singletons, ranging from a RR of 2.71 for postneonatal mortality to a RR of 3.73 for late neonatal mortality. Generally, for birth weights of 2,800 g or less and gestational ages of 38 weeks or less, twins had lower combined birth weight and gestational age mortality rates and lower RRs. Between 1,900 and 2,799 g, mortality rates decreased then increased with advancing gestation between 31 and 42 weeks both more severely and consistently for twins than for singletons. In conclusion, twins have lower birth weight and gestational age-specific mortality rates and RRs than singletons below 2,800 g and 39 weeks. The “U”-shaped pattern of mortality beyond 38 weeks gestation, particularly for twins with birth weights below 2,500 g, reflects the combined influence of growth retardation and advancing gestation on mortality. The lowest mortalityfor twins is achieved at birth weights of 2,500-2,799gat35-38 weeks gestation. Only 1 in 7 twins is born within this “ideal window.” Efforts at reducing twin mortality should be directed toward reducing intrauterine growth retardation and achieving optimal timing for delivery.     

A case-control comparison of the effectiveness of betamethasone to prevent neonatal morbidity and mortality in preterm twin and singleton pregnancies

We compared the effectiveness of antenatal betamethasone for the prevention of neonatal morbidity and mortality in preterm twin and singleton gestations. We conducted a case-control study of women with twin versus singleton gestations who received betamethasone for risk of prematurity in a university-affiliated, community-based, tertiary care center between 1997 and 2005. Cases were identified from clinical care and pharmacy databases, then matched for neonatal gender and gestational age (GA) at delivery. Sixty cases and 60 controls of deliveries occurring between 24 and 34 weeks' gestation were identified. The mean GA was 30.4 +/- 2.7 weeks. There were no differences between the groups in maternal demographics (with the exception of maternal age), birth weight, head circumference, Apgar scores, need for mechanical ventilation, days on ventilator, intraventricular hemorrhage grade 3 or 4, necrotizing enterocolitis suspected sepsis, total days in neonatal intensive care unit, or neonatal deaths. No differences in major morbidities or mortality were found in singletons versus twins. Concerns that the added maternal plasma volume in multiple gestations could lessen the neonatal benefits of antenatal betamethasone were not substantiated. This study may be affected by beta-error due to small sample size and sampling bias as a result of a retrospective study.     

The interval to spontaneous delivery following discontinuation of maintenance tocolysis.

OBJECTIVE: To determine the interval to spontaneous delivery following discontinuation of continuous subcutaneous terbutaline (SQT). METHODS: Singleton and twin gestations receiving outpatient preterm labor management services with SQT were identified from a database. Patients having SQT discontinued at 33.0-35.9 weeks (in a stable condition, not hospitalized and with known cervical status at discontinuation) with subsequent spontaneous labor and delivery were included (n = 1420). Data were compared by gestation type, week of SQT discontinuation and cervical dilatation using Kruskal-Wallis and Fisher's exact test analyses (p < 0.05 statistically significant). RESULTS: Spontaneous preterm delivery occurred in 63.0% of singletons and 87.9% of twins. Although stable at SQT discontinuation, 32.5% of singletons and 59.9% of twins delivered within three days. The interval from discontinuation of SQT to delivery was less for twin than singleton gestations (5.1 +/- 6.5 vs. 11.0 +/- 10.5 days, respectively, p < 0.001). CONCLUSIONS. Preterm discontinuation of SQT should be avoided if additional pregnancy prolongation is desired.     

A case-control study of 1253 twin pregnancies from a 1982-1987 perinatal data base

In one regional perinatal network between 1982-1987, 101,506 women delivered infants greater than 500 g, of which 1253 were twin pregnancies (1.2%). This latter group was compared statistically with a 5% random sample of the singletons (N = 5119). The results showed that the women with twin pregnancies were slightly older, had a higher parity, gained more weight during the gestation, and had a heavier body weight at delivery. Twin pregnancies were complicated by increases in hypertension (odds ratio 2.5; 95% confidence interval 2.1-3.1), abruption (odds ratio 3.0; 95% confidence interval 1.9-4.7), and anemia (odds ratio 2.4; 95% confidence interval 1.9-3.0). There was no increased risk of pyelonephritis, placenta previa, or diabetes mellitus in mothers with twins. The twin pregnancies delivered earlier and the infants were smaller, had lower Apgar scores, and were at increased risk for congenital anomalies. Fetal and neonatal mortality rates were significantly increased in the twin infants; the perinatal mortality rates for twin A and twin B were 48.8 and 64.1, respectively, compared with 10.4 per 1000 births for the singleton controls. When the twin infants A and B were of similar weight, they had a similar perinatal mortality (odds ratio 1.0; 95% confidence interval 0.6-1.8). For infants less than 2500 g, twins A and B had lower fetal and neonatal mortality rates than did singletons, but twins heavier than 2500 g were at increased risk of perinatal death.     

Neurodevelopmental outcomes of twins

In population-based studies, the prevalence of neurodevelopmental disability is consistently higher in twins than singletons. This is largely because birth weight and gestational age (GA) distributions of twin births are shifted to the left when compared with singleton births, and lower birth weight and lower GA are associated with increased risk of neurodevelopmental disability. From a pathophysiologic perspective, a question of interest is whether neurodevelopmental outcomes of twins differ from singletons after controlling for covariates. If significant differences in outcomes persist, this would suggest that the twining process itself or something intrinsic to shared life in the womb may be responsible for observed differences. From a clinical perspective, when counseling parents at risk for preterm delivery of twins, it is useful to understand how twin outcomes compare relative to singleton outcomes at the same birth weight or GA. The purpose of this review is to examine the long-term neurodevelopmental outcomes of twins compared with singletons with control for important covariates.     

Hypertensive disorders in twin versus singleton gestations. National Institute of Child Health and Human Development Network of Maternal-Fetal Medicine Units

OBJECTIVE: This study was undertaken to compare rates and severity of gestational hypertension and preeclampsia, as well as perinatal outcomes when these complications develop, between women with twin gestations and those with singleton gestations. STUDY DESIGN: This was a secondary analysis of prospective data from women with twin (n = 684) and singleton (n = 2946) gestations enrolled in two separate multicenter trials of low-dose aspirin for prevention of preeclampsia. End points were rates of gestational hypertension, rates of preeclampsia, and perinatal outcomes among women with hypertensive disorders. RESULTS: Women with twin gestations had higher rates of gestational hypertension (relative risk, 2.04; 95% confidence interval, 1.60-2.59) and preeclampsia (relative risk, 2. 62; 95% confidence interval, 2.03-3.38). In addition, women with gestational hypertension during twin gestations had higher rates of preterm delivery at both <37 weeks' gestation (51.1% vs 5.9%; P <. 0001) and <35 weeks' gestation (18.2% vs 1.6%; P <.0001) and also had higher rates of small-for-gestational-age infants (14.8% vs 7. 0%; P =.04). Moreover, when outcomes associated with preeclampsia were compared, women with twin gestations had significantly higher rates of preterm delivery at <37 weeks' gestation (66.7% vs 19.6%; P <.0001), preterm delivery at <35 weeks' gestation (34.5% vs 6.3%; P <.0001), and abruptio placentae (4.7% vs 0.7%; P =.07). In contrast, among women with twin pregnancies, those who remained normotensive had more adverse neonatal outcomes than did those in whom hypertensive complications developed. CONCLUSIONS: Rates for both gestational hypertension and preeclampsia are significantly higher among women with twin gestations than among those with singleton gestations. Moreover, women with twin pregnancies and hypertensive complications have higher rates of adverse neonatal outcomes than do those with singleton pregnancies.