Early prediction of preterm birth for singleton, twin, and triplet pregnancies

OBJECTIVES: To create prediction models of early preterm birth for singletons, twin, and triplet pregnancies. STUDY DESIGN: We used a historical cohort study with the 1996 birth registration data for singletons and the 1995-1997 linked birth/infant death dataset for multiple births of the United States. Preterm birth was defined as gestational age <32 completed weeks. Eligible study subjects were randomly allocated to two groups: one group (80% subjects) for the creation of the prediction models, and the other group (20% subjects) for the validation of the established prediction models. Multivariate logistic regressions were used to establish the prediction models. We further assessed the sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) of the established prediction models with different cut-off values in the validation group. RESULTS: The sensitivity, specificity, PPV, and NPV of the established model were 24.58, 93.54, 5.91, and 98.69%, respectively for singletons, 64.66, 57.04, 16.29, and 92.59%, respectively for twins, and 63.57, 53.58, 42.96, and 72.78%, respectively for triplets. CONCLUSION: The prediction models of early preterm birth for singleton, twin, and triplet pregnancies created by this study could be useful for obstetricians to identify women being at high risk of preterm birth at early gestation.     

A parsimonious explanation for intersecting perinatal mortality curves: understanding the effect of plurality and of parity

BACKGROUND: Birth weight- and gestational age-specific perinatal mortality curves intersect when compared across categories of maternal smoking, plurality, race and other factors. No simple explanation exists for this paradoxical observation. METHODS: We used data on all live births, stillbirths and infant deaths in Canada (1991-1997) to compare perinatal mortality rates among singleton and twin births, and among singleton births to nulliparous and parous women. Birth weight- and gestational age-specific perinatal mortality rates were first calculated by dividing the number of perinatal deaths at any given birth weight or gestational age by the number of total births at that birth weight or gestational age (conventional calculation). Gestational age-specific perinatal mortality rates were also calculated using the number of fetuses at risk of perinatal death at any given gestational age. RESULTS: Conventional perinatal mortality rates among twin births were lower than those among singletons at lower birth weights and earlier gestation ages, while the reverse was true at higher birth weights and later gestational ages. When perinatal mortality rates were based on fetuses at risk, however, twin births had consistently higher mortality rates than singletons at all gestational ages. A similar pattern emerged in contrasts of gestational age-specific perinatal mortality among singleton births to nulliparous and parous women. Increases in gestational age-specific rates of growth-restriction with advancing gestational age presaged rising rates of gestational age-specific perinatal mortality in both contrasts. CONCLUSIONS: The proper conceptualization of perinatal risk eliminates the mortality crossover paradox and provides new insights into perinatal health issues.     

The changing epidemiology of multiple births in the United States

OBJECTIVE: To describe changes in the epidemiology of multiple births in the United States from 1980 to 1999 by race, maternal age, and region; and to examine the impact of these changes on birth weight-specific infant mortality rates for singleton and multiple births. METHODS: Retrospective univariate and multivariable analyses were conducted using vital statistics data from the National Center for Health Statistics. RESULTS: Between 1980 and 1999, the overall multiple birth ratio increased 59% (from 19.3 to 30.7 multiple births per 1000 live births, P <.001), with rates among whites increasing more rapidly than among blacks. Women of advanced maternal age, especially those aged 30-34, 35-39, and 40-44 experienced the greatest increases (62%, 81%, and 110%, respectively). Although all regions of the United States experienced increases in multiple birth ratios between 1991 and 1999, the Northeast had the highest twin (33.9 per 1000 live births) and higher order birth ratios (280.5 per 100,000 live births), even after adjusting for maternal age and race. Between 1989 and 1999, multiple births experienced greater declines in infant mortality than singletons in all birth weight categories. Consequently, very low birth weight and moderately low birth weight infant mortality rates among multiples were lower than among singletons. CONCLUSION: It is important to understand the changing epidemiology of multiple births, especially for women at highest risk (advanced maternal age, white race, Northeast residents). The attribution of infertility management requires further study. The differential birth weight-specific infant mortality for singletons and multiples demonstrates the importance of stratifying by plurality when assessing perinatal outcomes.     

Neonatal outcome in pregnancies from ovarian stimulation

OBJECTIVE: To study the neonatal outcome in pregnancies after ovarian stimulation, not including in vitro fertilization. The outcomes studied were multiple birth, preterm birth, and low birth weight among singletons, congenital malformations, and infant death. METHODS: We identified 4029 women who delivered between 1995-1999 after ovarian stimulation alone and compared them with 438,582 women who neither had ovarian stimulation nor in vitro fertilization. We controlled for the confounding effect of year of birth, maternal age, parity, and length of subfertility before the pregnancy. RESULTS: The twinning rate was 5.9% in the study group and 1.2% in the control group. The triplet rate was 0.5% in the study group and 0.02% in the control group. A nearly doubling of the rate of monozygotic twinning was indicated in the study group compared with the control group. There was an excess of singleton preterm births and low birth weight infants in the study group, but this was mainly explainable by confounding of maternal age, parity, and subfertility. The rates of congenital malformations and perinatal deaths were increased, also mainly explainable by maternal characteristics. No increase in specific types of congenital malformations was seen. CONCLUSION: As the deviations in neonatal outcome after ovarian stimulation alone were reduced or disappeared when the confounding of maternal age, parity, and subfertility was taken into consideration, there is probably little direct effect of the stimulation procedure as such.     

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.     

Pregnancy-induced hypertension is associated with lower infant mortality in preterm singletons

OBJECTIVE: To assess the association between pregnancy-induced hypertension (PIH) and infant mortality. DESIGN: Retrospective cohort study. SETTING: Birth and infant death registration dataset of the USA. POPULATION: A total of 17,432,987 eligible, liveborn singleton births in 1995-2000. METHODS: Multivariate logistic regression was applied to evaluate the association between PIH and infant mortality, with adjustment of potential confounders. MAIN OUTCOME MEASURES: Infant death (0-364 days) and its three components: early neonatal death (0-6 days), late neonatal death (7-27 days), and postneonatal death (28-364 days). RESULTS: There was a significant reduction in infant mortality associated with PIH in early preterm infants (OR = 0.59, 95% CI: 0.56-0.63) and in late preterm infants (OR = 0.80, 95% CI: 0.73-0.87), but a significant increase in term infants (OR = 1.08, 95% CI: 1.02-1.14). Both in early preterm and late preterm births, early neonatal mortality (OR = 0.38, 95% CI: 0.34-0.42; OR = 0.68, 95% CI: 0.61-0.77) and late neonatal mortality (OR = 0.59, 95% CI: 0.50-0.70; OR = 0.76, 95% CI: 0.61-0.96) were decreased in infants born to mothers with PIH compared with those born to mothers with normal blood pressure. The PIH-associated reduction in neonatal mortality among preterm singletons was stronger in small-for-gestational-age infants than in normal growth infants and stronger in infants born to nulliparous women than in those born to multiparous women. CONCLUSIONS: PIH is associated with lower risk of infant death in preterm births but higher risk in term births.     

New-onset hypertension in late pregnancy and fetal growth: different associations between singletons and twins.

OBJECTIVE: To compare the effects of new-onset hypertension (NOH) in late pregnancy on fetal growth in singletons and twins. METHODS: A retrospective cohort study was conducted to evaluate the effect of NOH on fetal growth in 17, 720, 900 singletons and 463, 104 twins born in the United States between 1995 and 2000. RESULTS: NOH was associated with lower mean birth weight in both preterm and term singletons. Increased risk of low birth weight and decreased risk of high birth weight was associated with NOH in preterm and term singletons. NOH was associated with increased risk for small-for-gestational-age (SGA) births and decreased risk for large-for-gestational-age (LGA) births in preterm singletons, whereas it was associated with increased risk of both SGA and LGA births in term singletons. NOH was associated with higher mean birth weight in early preterm twins, and lower mean birth weight in term twins. Decreased risk for low birth weight was found in the NOH group among early preterm twins, and increased risk for low birth weight in term twins. NOH was associated with increased risk of SGA births and decreased risk for large-for-gestational-age (LGA) births in early preterm twins, while increased risk of SGA births in term twins. CONCLUSION: NOH is associated with slower fetal growth in singletons delivered at different gestational ages, but the effect varies in twins depending on gestational age at delivery with faster growth in early preterm twins.     

Sudden infant death syndrome among twin births: United States, 1995-1998.

OBJECTIVES: To compare the incidence and risk factors for sudden infant death syndrome (SIDS) in twin and singleton births and to estimate the concordance of SIDS in twins. STUDY DESIGN: A cohort analysis using the National Center for Health Statistics Linked Birth and Infant Death files (1995-1998). RESULTS: Twins had higher SIDS rate (1.3/1000 live births) compared to singletons (0.7/1000 live births), relative risk: 1.9, 95% confidence interval: 1.68, 2.01. Male and small- for-gestational age infants as well as infants of black, unmarried, and smoking mothers were at increased risk for SIDS in both twins and singletons. Placental abnormalities also were associated with SIDS in singletons and twins, although this association failed to achieve statistical significance in twins. There is a higher rate of SIDS in the second twin after a first twin SIDS. CONCLUSIONS: Twins are at higher risk of SIDS than are singletons. Overall, the epidemiology of SIDS in twins is quite similar to that seen in singletons.     

The effect of placenta previa on neonatal mortality: a population-based study in the United States, 1989 through 1997

OBJECTIVE: The purpose of the study was to explore the associations of placenta previa with preterm delivery, growth restriction, and neonatal survival. STUDY DESIGN: A retrospective cohort study was performed of live births in the United States (1989-1991 and 1995-1997) that used the national linked birth/infant death records from 22,368,235 singleton pregnancies. The diagnosis of previa was restricted to those live births that were delivered (> or =24 weeks) by cesarean delivery. We evaluated gestational age and birth weight-specific risk of neonatal deaths (within the first 28 days) in relation to placenta previa. Fetal growth was assessed in centiles of birth weight (<3rd, 3rd-4th, 5th-9th, 10th-90th, and >90th centile), adjusted for gestational age. All analyses were adjusted for the confounding effects of the year of delivery, maternal age, gravidity, education, prenatal care, marital status, and race/ethnicity. RESULTS: Placenta previa was recorded in 2.8 per 1000 live births (n = 61,711). Neonatal mortality rate was 10.7 with previa, compared with 2.5 per 1,000 among other pregnancies (relative risk, 4.3; 95% confidence interval, 4.0,4.8). At 28 to 36 weeks, babies born to women with placenta previa weighed, on average, 210 g lower than babies born to women without placenta previa (P <.001). Compared with babies born to women without previa, the risk of death from placenta previa was lower among preterm babies (<37 weeks of gestation), with a crossover at 37 weeks where the mortality rate was higher for babies born to women with placenta previa than for babies born to women without placenta previa. This crossover also persisted in an analysis by birth weight and term births (delivered at > or =37 weeks of gestation). Mortality rates for term births were higher among babies born to women with placenta previa than among babies born women without placenta previa who were at the 10th to 90th centile (relative risk, 1.9; 95% confidence interval, 1.3, 2.8), and those at >90th centile (relative risk, 3.6; 95% confidence interval, 1.3, 9.6). Among preterm births, however, placenta previa was not associated with increased neonatal mortality by fetal growth centiles. CONCLUSION: The risk of neonatal mortality was higher for babies born to women with placenta previa than for babies born to women without placenta previa who were delivered at > or =37 weeks of gestation. Pregnancies that are diagnosed with placenta previa must be monitored carefully, especially as they approach term.     

Obstetrics and perinatal outcome of adolescent nulliparous pregnant women

OBJECTIVE: To study obstetrics and perinatal outcome in nulliparous teenage singleton pregnancies at a referral teaching hospital in the eastern province of Saudi Arabia. METHOD: All singleton births during 1996-2000 of nulliparous mothers aged < or =17 years at King Fahd University Hospital were reviewed (n = 102) and compared with births of a control group of nulliparous mothers aged 20-24 years who delivered during the same period (n = 102). RESULTS: The incidence of nulliparous teenage pregnancies was 0.8%. As compared with women aged 20-24 years, women of 17 years or less were at higher risk of very preterm birth (p < 0.05). The 5-min Apgar scores were not different between the two groups. Babies born to younger mothers had a significantly lower birth weight than those born to older mothers (p < 0.001); the incidence of a low birth weight (<2,500 g) was significantly lower in the control group (p < 0.04). There were no significant differences in distribution of mode of delivery, admission to the special care baby unit, antenatal complications, cesarean section indications, perinatal mortality rate, and early neonatal complications between the two groups. CONCLUSION: The increase in the very preterm births and the subsequently lower birth weight observed in nulliparous teenage women suggest that the maternal age may be a risk factor for very preterm births and associated long-term hazards.     

Pregnancy-induced hypertension and infant mortality: Roles of birthweight centiles and gestational age

OBJECTIVE: To assess the effect of pregnancy-induced hypertension (PIH) on infant mortality in different birthweight centiles (small for gestational age [SGA], appropriate for gestational age [AGA], and large for gestational age [LGA]) and gestational ages (early preterm, late preterm, and full term). DESIGN: Retrospective cohort study. SETTING: Linked birth and infant death data set of USA between 1995 and 2000. POPULATION: A total of 17 464 560 eligible liveborn singleton births delivered after 20th gestational week. METHODS: Multivariate logistic regression models were applied to evaluate the association between PIH and infant mortality, with adjustment of potential confounders stratified by birthweight centiles and gestational age. MAIN OUTCOME MEASURE: Infant death (0-364 days) and its three components: early neonatal death (0-6 days), late neonatal death (7-27 days), and postneonatal death (28-364 days). RESULTS: PIH was associated with decreased risks of infant mortality, early neonatal mortality, and late neonatal mortality in both preterm and term SGA births, and PIH was associated with lower postneonatal mortality in preterm SGA births. PIH was associated with decreased risks of infant mortality, early neonatal mortality, late neonatal mortality and postneonatal mortality in preterm AGA births. Decreased risk of infant mortality and early neonatal mortality was associated with PIH in early preterm LGA births. CONCLUSIONS: The association between PIH and infant mortality varies depending on different birthweight centiles, gestational age, and age at death. PIH is associated with a decreased risk of infant mortality in SGA births, preterm AGA births, and early preterm LGA births.     

Effect on neonatal outcomes in gestational hypertension in twin compared with singleton pregnancies

OBJECTIVE: We tested the hypothesis that gestational hypertension may have a more benign effect on neonatal outcomes in twin compared with singleton pregnancies, because the elevated blood pressure in twin pregnancies may partly or merely reflect the extra demand for blood supply. METHODS: A retrospective cohort study of 102,988 twin and 5,523,797 singleton live births using the U.S. birth cohort linked birth and infant death data sets, 1998-2000. Main outcomes are relative risks (RRs) of adverse neonatal outcomes: preterm birth, intrauterine growth restriction (less than the third percentile), low 5-minute Apgar score (less than 4), and neonatal death comparing gestational hypertensive with no-event healthy pregnancies for twins and singletons. RESULTS: For singletons, crude RRs (95% confidence intervals) comparing gestational hypertensive with healthy pregnancies were 2.23 (2.20-2.25) for preterm birth (17.4 compared with 7.8%), 2.49 (2.45-2.53) for intrauterine growth restriction (7.4 compared with 3.0%), 1.33 (1.21-1.45) for low 5-minute Apgar score (2.6 compared with 2.0 per 1,000), and 1.07 (0.96-1.19) for neonatal death (1.9 compared with 1.8 per 1,000), respectively. For twins, the corresponding RRs were much lower or showed reversed associations: 1.21 (1.19-1.24) (63.6 compared with 52.4%), 1.04 (0.98-1.11) (16.4 compared with 16.4%), 0.32 (0.23-0.46) (4.1 compared with 12.7 per 1,000), and 0.21 (0.14-0.30) (3.6 compared with 17.2 per 1,000), respectively. The adjusted odds ratios showed a similar risk pattern in twin compared with singleton pregnancies after controlling for maternal race, age, education, marital status, parity, smoking, alcohol use, perinatal care use, and mode of delivery. CONCLUSION: Gestational hypertension has a much more benign effect on neonatal outcomes in twin compared with singleton pregnancies. There might be a need for twin- or multiple fetus-specific recommendations for hypertension management in pregnancy, but further interventional studies are needed to test the hypothesis. LEVEL OF EVIDENCE: II-2.     

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.     

Role of vaginal infection in fetal and neonatal mortality

Preterm delivery is the chief problem in obstetrics today and the main determinant of infant mortality and morbidity. Despite the dramatic decrease in infant mortality rate during the past several years, the percentage of preterm (<37 weeks gestation) and low birth weight (LBW) (<2500) rates remain elevated. Approximately 10% of all births are preterm, with a rate of 1-2% of infant born before the end of the 32 weeks of gestation and with a weight <1500 g. Despite the importance of the problem, the majority of preterm live births remain unexplained, and programmatic attempts at reversing the high level of preterm births have not been successful. Numerous studies have linked bacterial vaginosis, chorioamniotitis and endometritis with preterm birth and LBW, especially among African women. The number of preterm live births among African women is twice the one among Caucasians. Bacterial vaginosis is an independent risk factor for preterm and LBW births and the mechanism by which bacterial vaginosis causes the preterm birth of an infant with LBW is unknown. The aim of this article was to underline the importance of the treatment and early identification of vaginal infection, in particular if due to bacterial vaginosis, as it can have a substantial affect on the incidence of preterm delivery with LBW.     

Comparison of active phase labor between triplet, twin, and singleton gestations

OBJECTIVE: To characterize the active phase of labor in triplet pregnancies and compare it with gestational age-matched twins and singletons. METHODS: Active phase rates were calculated beginning at 5 cm of dilation for women with triplet gestations longer than 24 weeks who labored and reached the second stage. Twin and singleton cohorts that also completed the first stage of labor were matched for gestational age at delivery (+/-1 week), parity, and epidural use. Intrapartum variables included oxytocin use (induction or augmentation, duration of infusion, and maximum dosage), cervical dilation at membrane rupture, and active phase dilation rate. RESULTS: Thirty-two triplet pregnancies met inclusion criteria between January 1994 and September 1998 and were each compared with twin and singleton cases in a 1:2 ratio. Triplet and twin active phase rates, while similar (1.8 versus 1.7 cm/hour, respectively), were significantly lower than the mean singleton dilation rate (2.3 cm/hour, P =.02). No other intrapartum variables differed between the three groups. Despite controlling for gestational age at delivery, mean birth weights were significantly higher in singletons and correspondingly lower in twins and triplets (2,493 versus 2,112 and 1,968 g, respectively; P =.001). An analysis of active phase dilation rates as a function of the cumulative birth weight per pregnancy demonstrated an inverse correlation, with slower progress in active labor associated with increasing total fetal weight (R = -.24; P =.002). CONCLUSIONS: Triplet and twin active phase dilation proceeds at a slower rate than that observed in singleton pregnancies. The rate of active phase dilation is inversely correlated to total fetal weight.     

Is a poor pregnancy outcome related to young maternal age? A study of teenagers in Estonia during the period of major socio-economic changes (from 1992 to 2002)

OBJECTIVE: To assess the risk of low birth weight, preterm birth, stillbirth, neonatal and postneonatal death among primiparous teenagers having singleton births, compared to a similar group of women aged 20-24 years in Estonia during the period of major socio-economic changes. STUDY DESIGN: Registry study using the data from the Estonian Medical Birth Registry (EMBR) for years 1992-2002; EMBR data were linked with infant deaths in the Estonian Mortality Database. Study population included 51,890 women aged 13-24 years, arranged into three groups: < or =17, 18-19, and 20-24. Crude odds ratios (OR), adjusted ORs and their 95% confidence intervals (CI) for the different outcomes were estimated using multiple logistic regression analysis. RESULTS: Compared with women aged 20-24 years, the risk of low birth weight and preterm birth was higher among teenagers. The risk of low birth weight and preterm birth within the study group as a whole did not change during the study period. Increased risks in neonatal and postneonatal death among younger teenagers of an age of 17 years and less seem to be a result of prematurity. CONCLUSIONS: Despite major socio-economic changes resulting in improvements in obstetric care and growth in incomes, teenagers remained a higher risk group.     

Prospective risk of fetal death in singleton, twin, and triplet gestations: implications for practice

OBJECTIVE: To evaluate the prospective risk of fetal death in singleton, twin, and triplet pregnancies and to compare this risk with fetal and neonatal death rates. METHODS: We analyzed 11,061,599 singleton, 297,622 twin, and 15,375 triplet gestations drawn from the 1995-1998 National Center for Health Statistics linked birth and death files. Prospective risk of fetal death was expressed as a proportion of all fetuses still at risk at a given gestational age and compared with fetal death rate. Fetal death risk and neonatal death rates were represented graphically for singletons, twins, and triplets. RESULTS: The prospective risk of fetal death at 24 weeks was 0.28 per 1000, 0.92 per 1000, and 1.30 per 1000 for singletons, twins, and triplets, respectively. At 40 weeks, the corresponding risk was 0.57 per 1000 and 3.09 per 1000 for singletons and twins, respectively and, at 38 or more weeks, 13.18 per 1000 for triplets. Plots of gestation-specific prospective risk of fetal death and neonatal mortality converged for singletons and twins at term but crossed for triplets at approximately 36 weeks' gestation. CONCLUSION: Prospective risk of fetal death is greater for triplets and twins than for singletons and greater for triplets than for twins during the third trimester. The pattern corroborates with uteroplacental insufficiency as a suspected underlying mechanism. When prospective risk of fetal death exceeds neonatal mortality risk, delivery might be indicated. When this model is used, this data set suggests that it might be reasonable to consider delivery of twins by 39 weeks and triplets by 36 weeks to improve perinatal outcome.     

Triplet pregnancies and their aftermaths. Part I: Basic considerations

Until recently, triplets were an infrequent occurrence. With the development of ovulation-inducing medications and then assisted reproductive technology (ART), the triplet birth rate in maternal age ranges over 24 years has multiplied three- to fiftyfold. The first review of the clinical aspects of triplet pregnancies was published in 1988. Since then, more data reported on such births have revealed a consistent triad of preterm delivery, low birth weight, and very low birth weight, plus increased maternal risks. This article details comparative risks to mothers and children using population-based data comparing differential outcomes in singletons, twins, and triplets; an extensive review of recent triplet publications is provided in the references.     

Birth weight by gestational age in twin pregnancies: analysis of 661 pairs.

The mortality of twin infants is four to five times higher than that of singletons, and one-half to two-thirds of all twins weigh < 2,500 g at birth. The appropriate interpretation of fetal growth throughout pregnancy is dependent upon the availability of adequate standards. We reviewed 661 pairs of live twin infants born at Chang Gung Memorial Hospital from 1979 to 1990. The frequency of twin births was 1.17% (1:86), and the ratio of males to females was 1.03. The frequency of preterm births (< 37 weeks) was 36.9%, the frequency of low birth weight (< 2,500 g) was 47.9% and very low birth weight (< 1,500 g) was 6.7%. A fetus grows most rapidly from the 32nd to the 35th week of gestation (200 g per week). The growth was 145 g per week from the 28th to the 32nd week and from the 35th to the 38th week of gestation. After the 38th week, the mean birth weight increased by only 35 g per week. Compared with a singleton birth, the mean birth weight of twins was about 100 g lighter during the 28th to the 32nd week, then the difference increased gradually to about 500 g at term.