Preterm Birth In Twins Research Articles

The rate of preterm twin births (22-27 weeks) as a criterion for measuring the quality of prenatal care.

While the true figures are not well established, outcomes of twin pregnancies are directly dependent on a small number of preterm births between 22 and 27 weeks. Observation of perinatal outcomes in twin pregnancies yields two contradictory results. Firstly, it shows an improvement in perinatal mortality figures. Secondly, it reveals an increase in the rates of preterm deliveries. These findings result from the observation of 783 twin pregnancies followed and delivered in a level 3 perinatal centre in Paris between 1993 and 1998. Women followed since the beginning of pregnancy through the outpatient clinic of the institution are included in this number, as are women who were referred or transferred to the centre at a later date due to complications, This analysis reflects the influence of two contrasting policies. The first, and less recent policy is devoted to the prevention of preterm births, and is reflected by the low number of extremely preterm deliveries at 22-32 weeks. The second is the effect of our new approach to the prevention of foetal deaths in relation to foetal growth retardation in twins which has resulted in increased medical intervention such as the induction of labour or scheduled Caesarean birth. This has resulted in an increase in twin preterm births from 33 to 36 weeks, with the expected result of fewer foetal deaths.

The Rate of Preterm Twin Births (22–27 Weeks) As a Criterion for Measuring the Quality of Prenatal Care

AbstractWhile the true figures are not well established, outcomes of twin pregnancies are directly dependent on a small number of preterm births between 22 and 27 weeks. Observation of perinatal outcomes in twin pregnancies yields two contradictory results. Firstly, it shows an improvement in perinatal mortality figures. Secondly, it reveals an increase in the rates of preterm deliveries. These findings result from the observation of 783 twin pregnancies followed and delivered in a level 3 perinatal centre in Paris between 1993 and 1998. Women followed since the beginning of pregnancy through the outpatient clinic of the institution are included in this number, as are women who were referred or transferred to the centre at a later date due to complications. This analysis reflects the influence of two contrasting policies. The first, and less recent policy is devoted to the prevention of preterm births, and is reflected by the low number of extremely preterm deliveries at 22–32 weeks. The second is the effect of our new approach to the prevention of foetal deaths in relation to foetal growth retardation in twins which has resulted in increased medical intervention such as the induction of labour or scheduled Caesarean birth. This has resulted in an increase in twin preterm births from 33 to 36 weeks, with the expected result of fewer foetal deaths.

Causes and Consequences of Recent Increases in Preterm Birth Among Twins

In Brief OBJECTIVE To examine the causes and consequences of the recent increase in preterm birth among twins. METHODS We studied all twin births among residents of the province of Nova Scotia, Canada, between 1988 and 1997. Rates of preterm birth, preterm labor induction, preterm cesarean, small-for-gestational age (SGA), respiratory distress syndrome (RDS), stillbirth, perinatal mortality, and infant mortality were compared between past and more recent years. Changes in perinatal mortality were examined using logistic regression to adjust for the effects of other determinants. RESULTS The study included 2516 twin births (73 stillbirths and 2443 live births). The rate of preterm birth increased from 42.3% in 1988–1992 to 48.2% of twin live births in 1993–1997 (14% increase, P = .04). Twin live births born after preterm labor induction increased from 3.5% in 1988–1989 to 8.6% in 1996–1997 (P for trend = .007). Of live births between 34 and 36 weeks' gestation, the proportion born SGA decreased from 17.5% in 1988–1992 to 9.2% in 1993–1997 (P = .005). Over the same period, rates of prophylactic maternal steroid therapy increased substantially and rates of RDS declined. Perinatal mortality rates among pregnancies reaching 34 weeks decreased from 12.9 per 1000 total births in 1988–1992 to 4.2 per 1000 total births in 1993–1997 (P = .05). CONCLUSION Increases in preterm labor induction appear to be responsible for the recent increase in preterm birth among twins. These changes have been accompanied by decreases in perinatal morbidity and mortality among twin pregnancies that reach 34 weeks' gestation. Increased preterm labor inductions in twin pregnancies appear to be responsible for recent increases in the number of preterm twin births, and for declines in perinatal morbidity and mortality.

The preterm prediction study: maternal serum relaxin, sonographic cervical length, and spontaneous preterm birth in twins

The preterm prediction study: maternal serum relaxin, sonographic cervical length, and spontaneous preterm birth in twins

The Preterm Prediction Study: Maternal Serum Relaxin, Sonographic Cervical Length, and Spontaneous Preterm Birth in Twins

The risk of spontaneous preterm birth has been related to decreased cervical length and to increased serum relaxin. To explore a relationship between these findings, we used data collected from two prior studies to correlate relaxin levels with cervical length and risk of spontaneous preterm birth in women with twin pregnancies. In a secondary analysis of data collected in two previous observational studies of risk factors for preterm birth, relaxin levels in maternal serum and cervical length were measured at 24 (n= 188) and 28 (n= 145) weeks in women with spontaneous twin pregnancies. Relaxin, as a continuous variable, was related by logistic regression analysis to risk of spontaneous preterm birth before 37, 35, and 32 weeks' gestation, and by Spearman correlation coefficients to cervical length at 24 and 28 weeks. Cervical length at 24 weeks was known to be correlated with spontaneous preterm birth before 37, 35, and 32 weeks (P =.03,.01, and.002, respectively) in this study population. Cervical length did not correlate with relaxin levels at 24 (P=.601) or 28 (P=.304) weeks. Relationships between relaxin and spontaneous preterm birth were observed at 24 weeks for births before 37 weeks (odds ratio [OR] 1.56, 95% confidence interval [CI] 1.00, 2.44; P=.05), and at 28 weeks for births before 35 weeks (OR 1.97, 95% CI 1.05, 3.70; P=.034) and 32 weeks (OR 2.43, 95% CI 1.01, 5.83; P=.048). The absence of an association between relaxin and cervical length suggests that increased relaxin does not explain the inverse correlation between cervical length and spontaneous preterm birth in women with spontaneous twin pregnancies.

Twin birth weight discordance and risk of preterm birth

Objectives: Our purpose was to determine whether birth weight discordance is a risk factor for preterm birth of twins, and to further characterize the relationships involved. Study Design: Maternally linked 1978-1990 Missouri birth certificates were used to analyze gestations resulting in live twins. We used contingency tables and multiple logistic regression. Results: The degree of discordance correlated strongly with risk for live preterm birth but only for discordances >30% and preterm birth at <32 weeks’ gestation. Among 9479 pregnancies with discordance <30%, 9.5% ended in birth at <32 weeks’ gestation, versus 13.7% of 326 with discordance of 30% to 40% (P =.03) and versus 34.1% of 126 with discordance ≥40% (P <.001). There were 42 preterm twin births at <32 weeks’ gestation with discordances ≥40%. Of these, 51% were attributable to fetal growth restriction and 16% to large size for gestational age in one infant; in 72% the smaller twin was the second born, and in 86% the twins were like sex. The relative association between ≥40% discordance and preterm birth at <32 weeks’ gestation was strengthened (final odds ratio, 9.54; P <.0001) in a multivariate model containing other risk factors for delivery at <32 weeks’ gestation: black race, either twin small for gestational age, unmarried, teenage mother, number of male fetuses, like fetal sex, education <12 years, nulliparity, and cigarette smoking. Conclusions: Twin birth weight discordance has now clearly been demonstrated to be a risk factor for preterm birth. The effect was found particularly with discordances ≥40% before 32 weeks’ gestation. Discordance was usually attributable to fetal growth restriction, most often in the second-born twin. (Am J Obstet Gynecol 2000;183:63-7.)

Twin birth weight discordance and risk of preterm birth

Objectives: Our purpose was to determine whether birth weight discordance is a risk factor for preterm birth of twins, and to further characterize the relationships involved. Study Design: Maternally linked 1978-1990 Missouri birth certificates were used to analyze gestations resulting in live twins. We used contingency tables and multiple logistic regression. Results: The degree of discordance correlated strongly with risk for live preterm birth but only for discordances >30% and preterm birth at <32 weeks’ gestation. Among 9479 pregnancies with discordance <30%, 9.5% ended in birth at <32 weeks’ gestation, versus 13.7% of 326 with discordance of 30% to 40% (P =.03) and versus 34.1% of 126 with discordance ≥40% (P <.001). There were 42 preterm twin births at <32 weeks’ gestation with discordances ≥40%. Of these, 51% were attributable to fetal growth restriction and 16% to large size for gestational age in one infant; in 72% the smaller twin was the second born, and in 86% the twins were like sex. The relative association between ≥40% discordance and preterm birth at <32 weeks’ gestation was strengthened (final odds ratio, 9.54; P <.0001) in a multivariate model containing other risk factors for delivery at <32 weeks’ gestation: black race, either twin small for gestational age, unmarried, teenage mother, number of male fetuses, like fetal sex, education <12 years, nulliparity, and cigarette smoking. Conclusions: Twin birth weight discordance has now clearly been demonstrated to be a risk factor for preterm birth. The effect was found particularly with discordances ≥40% before 32 weeks’ gestation. Discordance was usually attributable to fetal growth restriction, most often in the second-born twin. (Am J Obstet Gynecol 2000;183:63-7.)

Perinatal deaths in a Norwegian county 1986-96 classified by the Nordic-Baltic perinatal classification: geographical contrasts as a basis for quality assessment.

Quality assessment of perinatal care can be carried out by classifying perinatal deaths. In the following we have analyzed the geographical contrasts in perinatal deaths according to the Nordic-Baltic perinatal death classification in a sparsely populated Norwegian county. All stillbirths (> or =28 weeks of gestation) and neonatal deaths (gestational age > or =22 weeks; death < or =28 days) in 1986-96 from Nordland county (240,000 inhabitants) were classified. For comparison the county was geographically divided into six general local hospital areas and one central hospital area. The classification showed a well acceptable inter and intra observer variation. One hundred and seventy-one stillbirths and 155 neonatal deaths were analyzed. The death rate (pr 1,000 births) for single, non-malformed, antenatal stillbirths was higher in the central hospital area than in the local hospital areas (3.22 vs. 2.02). The death rate for extreme preterm infants (22-27 weeks of gestation) was on the other hand higher in the local hospital areas (2.45 vs. 1.05). One of the general local hospital areas was singled out with an especially high neonatal death rate among extreme preterm infants. This was to some extent explained by the death of extreme preterm twins and triplets. The Nordic-Baltic perinatal death classification system is a consistent and reproducible tool also for studying perinatal death in restricted geographical areas. The observed contrasts in perinatal deaths were used as basis for programs aimed at improving perinatal care. The observation of an unexplained increased number of antenatal stillbirths in the central hospital area resulted in a program for prospective recording and better characterization of the placenta and umbilical cord. Proposals for a better antenatal program preventing extreme preterm birth of twins for the whole county has been launched. In utero transfer to a hospital with a neonatal intensive care unit seems crucial in improving the prognosis for these infants.

Effects of fetal sex and race on risk of very preterm birth in twins

OBJECTIVE: Our purpose was to determine whether the risk of twin preterm birth correlates with the number of male fetuses. STUDY DESIGN: Among 8109 white and 1884 black twin pregnancies in the Missouri Successive Pregnancy Birth/Death Data Set, 1978 through 1990, risk for preterm birth at various gestational ages was determined with 0, 1, or 2 male infants. RESULTS: Studied as individuals, white preterm twins <35 weeks’ gestation demonstrated a 9.2% excess of male fetuses ( P < .001). Adjusted for monozygosity, risk for preterm birth <35 weeks’ gestation was 15.7% in white female-female pairs, 17.9% in unlike-sex white fetuses, and 20.2% in white male-male pairs ( r = .999, P = .01). The effect was absent in black pregnancies and was unrelated to birth order, cesarean delivery, parity, twins’ weight differential, year, or season. CONCLUSIONS: In white twin gestations the observed linear relationship between the number of male fetuses and the likelihood of preterm birth <35 weeks’ gestation suggests a fetal mechanism for preterm birth <35 weeks’ gestation linked to fetal sex. Studies of mechanisms for preterm birth must stratify by fetal sex and race. (Am J Obstet Gynecol 1998;179:762-5.)

Association of Sociodemographic Variables With Risk for Very Preterm Birth in Twins

Objective: To assess the influence of maternal race, age, marital status, and education on risk for earlier and later preterm births in twin pregnancies. Methods: We analyzed 8109 white and 1906 black liveborn twin pregnancies in the Missouri Linked Sibship files for the years 1978–1990, using contingency tables and multiple logistic regression. Results: Black twin gestations had 1.61-fold (95% confidence interval [CI] 1.46, 1.76) greater risk than whites for preterm birth before 34 weeks’ gestation. However, there was no race difference after 33 weeks. Among whites, teen age, unmarried status, and education fewer than 12 years were independently associated with risk for delivery before 34 weeks in multivariate analysis (odds ratios [OR] 1.28–1.51, each P ≤ .001). These associations were diminished or absent for preterm births after 33 weeks’ gestation. White unmarried teen mothers with fewer than 12 years of education had 1.83-fold (95% CI 1.39, 2.40) greater risk for preterm birth before 34 weeks’ gestation compared with white married women more than 19 years of age with at least 12 years of education. In blacks, this difference was 1.47-fold (95% CI 1.13, 1.92). In both races, these differences were absent after 33 weeks’ gestation. Conclusion: Traditional sociodemographic risk factors were present for twin preterm birth, but mainly before 34 weeks’ gestation. This, together with previous data from Missouri Linked Sibship files, indicates that dominant pathogenic mechanisms of early preterm birth in twin gestations are likely to be different from those causing later preterm twin birth. Therefore, gestational age should be accounted for in future studies seeking to identify predictive factors or biomechanisms for twin preterm birth.

Association of Sociodemographic Variables With Risk for Very Preterm Birth in Twins

Association of Sociodemographic Variables With Risk for Very Preterm Birth in Twins

Gestational age-specific birthweight of twins in vital records.

Analysis of singleton preterm birth from vital statistics data is hampered by inaccurate gestational age dating. This is most notably evidence by the large fraction of implausibly high birthweights for gestational age given in birth records. Using natality statistics for New England, 1977-88, birthweight distributions were plotted for representative preterm gestations. Confounding by improbable birthweights was observed to be considerably less among preterm twin births than among preterm singleton births.

Gestational duration in the pregnancy after a preterm twin delivery

OBJECTIVE: This was a population-based medical birth registry investigation designed to study whether a preterm twin delivery portends a shorter gestation in a subsequent pregnancy. STUDY DESIGN: Data on all pregnancies and deliveries from 1973 to 1993 inclusive, stored at the Medical Birth Registry, the National Board of Health and Welfare, Stockholm, were analyzed. Information on gestational duration, estimated during pregnancy with or without ultrasonography in the second trimester, was analyzed for 2979 twin births followed by a singleton delivery. RESULTS: Gestation for women with a singleton pregnancy after a preterm twin birth in the twenty-eighth to thirty-sixth gestational week lasted about 39 ± 0.5 weeks (mean ± SEM). When the twin birth had taken place at term (37 to 42 weeks) the corresponding singleton gestation lasted about a week longer. When the twin birth occurred in gestational weeks 28 to 30, 31 to 33, or 34 to 36, the corresponding proportions of women who gave birth earlier than 37 weeks (20 to 27 weeks, only live births) in the subsequent singleton pregnancy were 9.8%, 7.0%, and 5.8%, respectively (χ 2 = 3.4, p > 0.05). CONCLUSIONS: It would appear that a preterm twin birth does not to any significant extent affect the gestational duration of a subsequent singleton pregnancy. (Am J Obstet Gynecol 1998;178:136-9.)

The preterm prediction study: Risk factors in twin gestations

OBJECTIVE: Our purpose was to determine the association between the presence of bacterial vaginosis, fetal fibronectin, and a short cervix and the risk of spontaneous preterm birth of twins. STUDY DESIGN: We prospectively screened 147 women with twins at 24 and 28 weeks' gestation for more than 50 potential risk factors for spontaneous preterm birth. We also measured cervical length with ultrasound scans and tested for the presence of bacterial vaginosis. Fetal fibronectin level was evaluated every 2 weeks from 24 to 30 weeks' gestation. Outcomes included spontaneous preterm birth at <32 weeks, <35 weeks, and <37 weeks. RESULTS: Among twin as compared with singleton pregnancies, a cervical length ≤25 mm was more common at both 24 and 28 weeks, a statistically significant difference. There were no significant differences in most other risk factors. Of the factors evaluated by means of univariate analysis at 24 weeks, only a short cervix (≤25 mm) was consistently associated with spontaneous preterm birth. The odds ratios and 95% confidence interval for spontaneous preterm birth at <32 weeks, <35 weeks, and <37 weeks were 6.9 (2.0 to 24.2), 3.2 (1.3 to 7.9), and 2.8 (1.1 to 7.7). At 28 weeks, a cervical length ≤25 mm was not a strong predictor of spontaneous preterm birth. At both 28 weeks (odds ratio, 9.4; confidence interval, 1.0 to 67.7) and 30 weeks (odds ratio, 46.1; confidence interval, 4.2 to 1381), a positive fetal fibronectin result was significantly associated with spontaneous preterm birth at <32 weeks. Bacterial vaginosis at 24 or 28 weeks was not associated with spontaneous preterm birth of twins. Multivariate analysis confirmed the association between cervical length ≤25 mm at the 24-week visit and spontaneous preterm birth and also confirmed that at 24 weeks the other risk factors were less consistently and often not statistically significantly associated with spontaneous preterm birth. Of the risk factors evaluated at 28 weeks, only a positive fetal fibronectin was associated with a significantly increased risk for spontaneous preterm birth. CONCLUSIONS: Most known risk factors for spontaneous preterm birth were not significantly associated with spontaneous preterm birth of twins. At 24 weeks, cervical length ≤25 mm was the best predictor of spontaneous preterm birth at <32 weeks, <35 weeks, and <37 weeks. Of the risk factors evaluated at 28 weeks, fetal fibronectin was the only statistically significant predictor of spontaneous preterm birth at <32 weeks. (Am J Obstet Gynecol 1996;175:1047-53.)

Prognostic significance of prior preterm twin delivery on subsequent singleton pregnancy

OBJECTIVE: Our purpose was to determine whether preterm birth of twins is associated with an increased risk of preterm birth in a subsequent singleton pregnancy. STUDY DESIGN: The Medical University of South Carolina perinatal database was accessed to identify a cohort of patients who were delivered of twins followed by a singleton gestation (1981 to 1993). Maternal transports were excluded to minimize referral bias. Preterm birth was defined as <37 weeks' gestation. Relative risks with 95% confidence intervals were calculated. RESULTS: One hundred forty-four patients were identified who were delivered of twins followed by a singleton gestation. Preterm delivery occurred in 86 (59.7%) of the twins and 21 (14.6%) of the subsequent singletons. Preterm birth of twins was associated with a significantly increased risk of preterm delivery in a subsequent singleton pregnancy (relative risk 2.87, 95% confidence interval 1.02 to 8.09). In the subset of women who were delivered of twins at <30 weeks' gestation, 42% of the subsequent singletons were delivered preterm (relative risk 6.11, 95% confidence interval 2.07 to 18.02). The relative risk of preterm birth of a singleton after delivery of twins between 30 and 34 weeks' gestation was 3.63 (95% confidence interval 1.02 to 12.92). However, if the preceding twins delivered between 34 and 37 weeks' gestation, the relative risk of preterm birth of the subsequent singleton was not significantly increased (relative risk 1.42, 95% confidence interval 0.40 to 5.01). CONCLUSIONS: Preterm birth of twins before 34 weeks' gestation is associated with a significant risk for preterm delivery in a subsequent singleton pregnancy. The magnitude of risk increases with decreasing gestational age of the preceding twin delivery. (A M J O BSTET G YNECOL 1996;174:1429-32.)

The origin and outcome of preterm twin pregnancies

To define the etiology of preterm twin births and determine the contribution of twin births to preterm birth and related morbidity and mortality. The March of Dimes Multicenter Prematurity and Prevention Study included a total of 33,873 women who delivered between 1982-1986, 432 (1.3%) of which delivered twins. Women were classified by reason for preterm birth and ethnicity. Neonates were classified as to stillbirth, neonatal death, and various short-term morbidities. A second data set from one center consisted of infants who weighed 1000 g or less, were born between 1979-1991, and survived to 1 year of age (n = 386, 15% twins); this was used to determine if twins and singletons born at comparable gestational ages have a similar risk for major developmental handicaps. Of the deliveries in the data set, 54% of twins were preterm compared with 9.6% among singletons. Of those born preterm, twins were born at a significantly earlier gestational age than were singletons. Only 2.6% of all neonates born were twins, but they represented 12.2% of all preterm infants, 15.4% of all neonatal deaths, and 9.5% of all fetal deaths. Spontaneous labor accounted for 54% of twin births, premature rupture of membranes accounted for 22%, and indicated deliveries accounted for 23%. Of the indicated preterm births in twins, 44% were due to maternal hypertension, 33% to fetal distress or fetal growth restriction, 9% to placental abruption, and 7% to fetal death. Comparing infants of similar gestational age, twins weighed less, but had a mortality equivalent to that of singletons after 29 weeks. Between 26-28 weeks' gestation, the risk of mortality for twins versus singletons was 1.6 (95% confidence interval 1.1-2.5). Preterm twins did not have significantly more respiratory distress syndrome, intraventricular hemorrhage, necrotizing enterocolitis, or other short-term morbidity than did preterm singletons. Twins who weighed 500-1000 g and survived to 1 year had a 25% rate of major developmental handicaps. However, when gestational age was controlled, the rate of major handicaps was not higher in twins than in singletons. Twins accounted for a disproportional amount of preterm birth and associated morbidity and mortality. Also, when preterm twins were compared with preterm singletons and corrected for their gestational ages, the rates of morbidity were similar. Preterm twins weighing less than 1000 g did not have an increased prevalence of major handicaps at 1 year of age compared with preterm singletons.

483 A 10-year review of preterm birth of twins at a referral tertiary care center

483 A 10-year review of preterm birth of twins at a referral tertiary care center