Common determinants of breech presentation at birth in singletons: a population-based study.

OBJECTIVE: To estimate common determinants of breech presentation at parturition. STUDY DESIGN: A population-based cohort study (between 1/1/2001 and 31/12/2010) was conducted among all women who delivered a singleton baby in breech presentation from 22 completed weeks of gestation. A binary logistic regression was used to determine independent feto-maternal characteristics of breech presentation at birth, adjusted odds ratios and 95% confidence intervals. Variables were: gestational age, birth weight, maternal age, parity and gender of the baby, presence or absence of a history of cesarean section, gestational diabetes, gestational hypertension, pregnancy after assisted reproduction technology and congenital malformations. RESULTS: From a population of 611,021 women; 28,059 were delivered in breech presentation (4.59%). Independent determinants of breech presentation at delivery were: gestational age and birth weight (the lower, the higher the incidence of breech at birth), parity (the frequency of breech decreased with increasing parity) and maternal age (the older the mother, the higher the odds for breech presentation). Women who had a scarred uterus, due to a previous cesarean section, women who gave birth to a female offspring and women whose baby showed a congenital malformation, were more prone to be delivered in breech presentation. CONCLUSION: Low gestational age and birth weight, advanced maternal age, a scarred uterus, a female baby and a baby with a congenital malformation increased the odds for singleton breech presentation at parturition. The latter gradually decreased with increasing parity.

Fetal and infant health outcomes among immigrant mothers in Flanders, Belgium.

OBJECTIVE: To compare fetal and infant mortality between immigrant and native-born mothers in Flanders, Belgium. METHODS: In a population-based study, data from 326 166 neonatal deliveries, collected by the Study Center for Perinatal Epidemiology and the Belgian Civil Birth Registration system between January 2004 and December 2008, were analyzed. Immigrant mothers were defined as women born in any country other than Belgium, and were grouped by country of origin according to the World Bank Atlas definition of low-, middle-, and high-income countries. Odds ratios (ORs) and 95% confidence intervals (CIs) were estimated to evaluate the association between immigration and fetal/infant outcome. RESULTS: In univariate analysis, fetal and infant mortality rates were significantly higher among immigrants than among native-born mothers (fetal: crude OR, 1.50; 95% CI, 1.29-1.75; infant: crude OR, 1.47; 95% CI, 1.29-1.67). Fetal/infant death rates were highest among mothers originating from low-income countries. In multivariate analysis, however, most differences became non-significant: only the early neonatal death rate remained significantly higher (adjusted OR, 1.30; 95% CI, 1.06-1.60), whereas the fetal death rate appeared lower (adjusted OR, 0.67; 95% CI, 0.57-0.80), among immigrant mothers. CONCLUSION: After adjustment for relevant characteristics, fetal/infant mortality was comparable between immigrant women and native-born women in Flanders.

Limiting the caesarean section rate in low risk pregnancies is key to lowering the trend of increased abdominal deliveries: an observational study.

BACKGROUND: As the rate of Caesarean sections (CS) continues to rise in Western countries, it is important to analyze the reasons for this trend and to unravel the underlying motives to perform CS. This research aims to assess the incidence and trend of CS in a population-based birth register in order to identify patient groups with an increasing risk for CS. METHODS: Data from the Flemish birth register 'Study Centre for Perinatal Epidemiology' (SPE) were used for this historic control comparison. Caesarean sections (CS) from the year 2000 (N = 10540) were compared with those from the year 2008 (N = 14016). By means of the Robson classification, births by Caesarean section were ordered in 10 groups according to mother - and delivery characteristics. RESULTS: Over a period of eight years, the CS rise is most prominent in women with previous sections and in nulliparous women with a term cephalic in spontaneous labor. The proportion of inductions of labor decreases in favor of elective CS, while the ongoing inductions of labor more often end in non-elective CS. CONCLUSIONS: In order to turn back the current CS trend, we should focus on low-risk primiparae. Avoiding unnecessary abdominal deliveries in this group will also have a long-term effect, in that the number of repeat CS will be reduced in the future. For the purpose of self-evaluation, peer discussion on the necessity of CS, as well as accurate registration of the main indication for CS are recommended.

Mothers' level of education and childbirth interventions: A population-based study in Flanders, Northern Belgium.

BACKGROUND: Interventions to influence the time and way to be born have been a global concern for decades. Yet, limited information is available on what drives these interventions and their variation in frequency among countries, institutions, and practitioners. The objective of this study was to examine to what extent first-time mothers' educational achievement contributes to the frequency of childbirth interventions. METHODS: Childbirth interventions, including induction of labor, cesarean section, instrumental delivery, and epidural analgesia, registered by the Flemish Study Center for Perinatal Epidemiology for Belgian-born nulliparous women from 1999 to 2006, were linked to the level of maternal education, recorded by the Belgian civil birth registration. Education was divided into four levels based on the highest diploma attained and adjusted for marital and occupational status. RESULTS: Frequencies of all interventions were inversely related to the level of maternal education. The effect remained after adjustment for birth year, maternal age, marital status, occupation, infant birthweight, gestational age, assisted conception, and type of hospital. Effect sizes between highest and lowest levels of education were relatively small for operative (31% vs 36%) and instrumental vaginal birth (20.7% vs 22.3%) compared with "initiated delivery" (defined as labor induction and prelabor cesarean section; 30.2% vs 40.3%) and epidural analgesia (66.8% vs 78.0%). The educational gradient in initiated delivery occurred at all gestational ages, contributing to lower gestational age and lower birthweight of term infants with decreasing levels of education. CONCLUSIONS: In an affluent society with universal and equitable access to maternity care, the more educated women are, the more likely they are to have a spontaneous labor and spontaneous birth without intervention. (BIRTH 38:3 September 2011).

Perinatal outcome of twins compared to singletons of the same gestational age: a case-control study.

Our objective was to determine the perinatal outcome of first- and second-born twins compared to singletons, born at the same gestational age. To that end we conducted a case-control study in Flanders (Northern Belgium). During a 10-year period (01.01.1999-31.12.2008), the entire twin population - 11,154 first- and 11,118 second-born twins (cases) - was compared to 22,228 singletons (controls) with respect to fetal and neonatal (0-27 days) mortality. Only case and control infants of ≥ 500 grams were included, which explained the unequal number of first- and second-born twins. Mothers and their infants of cases and of controls were derived from the Flemish perinatal database and were matched for maternal age and parity, gestational age and gender of the offspring. The main outcome measures were fetal and neonatal mortality according to gestational age. The frequency of fetal death was statistically significantly less frequent in preterm born twins than in singletons, except at term where the reverse was seen in second-born twins compared to controls. After adjustment for congenital malformations, the results stayed unchanged. Below 28 weeks gestation, singletons had a significantly lower neonatal mortality rate than twins that persisted after adjustment for congenital malformations: the first-born twin versus singleton OR 1.71 (1.17-2.51) and second-born versus singleton OR 2.09 (1.43-3.05). Between 28 and 32 weeks, the second-born twin showed a survival advantage over the control singleton. Between 32 and 36 6/7 weeks both twins had a significantly higher survival rate than the corresponding singleton controls. However, after adjustment for congenital malformations, the aforementioned differences between 28 and 36 6/7 weeks disappeared. When at term, twins and singletons had a comparable, though very low, neonatal death rate. These results confirm previous published data. In conclusion, we demonstrated that the neonatal death rate was lower for twins between 32 and 36 weeks (from 28 weeks for the second born twin) when compared to a singleton of the same gestational age. After adjusting for congenital malformations, there was no statistical significant difference.

Cross-country variation in stillbirth and neonatal mortality in offspring of Turkish migrants in northern Europe.

BACKGROUND: Diverse early-life mortality outcomes have been documented in immigrant populations in northern Europe. A recent meta-analysis has suggested that national integration policy is a key factor in understanding this heterogeneous pattern. In this study, we investigated the variation of stillbirth and neonatal mortality between societies in northern Europe in one minority population, the Turkish. METHOD: Data on stillbirth and neonatal deaths in 239 387 births during 1990-2005, where the mother was of Turkish origin, was drawn from birth registries or surveys in nine northern European countries. Rates were compared with births from mothers who were born in the society of residence. Logistic regression was used to calculate odds ratios adjusted for year of birth of the offspring. RESULTS: The risks for stillbirth were, or tended to be, elevated for Turkish mothers in all countries compared with the native population, with the highest risk in Austria (odds ratio (OR) 1.7; 95% confidence interval (CI) 1.4-2.1) and Switzerland (OR 1.6; 1.4-1.9). For neonatal mortality the results were heterogeneous, indicating no excess risk for Turkish-born children in the Netherlands, the UK and Norway, and elevated risks in Denmark (OR 1.3; 1.0-1.6), Switzerland (OR 1.3; 1.1-1.5), Austria (OR 1.4; 1.0-1.8) and Germany (OR 1.3; CI 1.2-1.5). CONCLUSION: This study suggests that preventable society-specific determinants are important for early-life mortality in Turkish migrants in Europe. An active integration policy is consistent with a favourable neonatal mortality outcome in continental Europe, but not with patterns in Scandinavia and the UK.

The higher the educational level of the first-time mother, the lower the fetal and post-neonatal but not the neonatal mortality in Belgium (Flanders).

OBJECTIVE: To assess, in a homogenous population of primiparous women, how fetal and infant (=first year of life) mortality varied by the mothers' level of education. STUDY DESIGN: We conducted an observational study in Flanders (Northern Belgium) involving 170,948 primiparous women who delivered in Flanders during the period 1999-2006, and their 174,495 babies. We linked the maternal education (3 levels) with a series of obstetrical and perinatal events, with special emphasis on fetal and infant death. A logistic regression analysis was performed to adjust for confounders. RESULTS: The incidence of fetal (0.21% - high level of education; 0.35% - medium level; 0.84% - low level) and infant mortality (0.32%; 0.41%; 0.70%, respectively), followed an inverse maternal educational gradient: higher with a lower level of education. However, neonatal death (0-27 days) was independent of the educational level of the mother. The age of the woman at delivery, the use of assisted reproductive technology and the incidence of twin birth increased while the rates of preterm birth (7.7% - high level; 8.9% - medium level; 10% - low level) and low birth weight (7.2%; 9.5%; 11.8%, respectively) decreased with the mother's educational level. CONCLUSION: Perinatal and obstetrical outcome differ according to the level of the education of the mother, which is a determinant of the incidence of fetal and post-neonatal death but not of early and late neonatal death (0-27 days).

Perinatal outcome of twin pregnancies in women of advanced age.

BACKGROUND: The aim of this study was to assess the outcome of twin pregnancies in women of advanced age (>or=35 years) compared with women aged 25-29 years old. METHODS: This population-based retrospective study compared perinatal outcome of twin pregnancies in primiparae aged 35 or older (N = 240) to that of twin pregnancies in primiparae aged 25-29 years (N = 940). Observed outcomes are adjusted for intermediate (mode of conception and hypertension during pregnancy) and confounding variables (level of education). The possible effect of zygosity and chorionicity was tested in a subset of this database, recorded in the East Flanders Prospective Twin Survey (EFPTS). RESULTS: In twin pregnancies, maternal age of 35 or over is associated with a lower incidence of preterm birth [adjusted odds ratio (AOR) 0.59, 95% confidence interval (CI) 0.44-0.79] and low birthweight (AOR 0.75, 95% CI 0.58-0.98) compared with younger women. Differences in zygosity and chorionicity between both cohorts do not seem to affect the result. CONCLUSIONS: In comparison with primiparae aged 25-29 years, perinatal outcome of twin pregnancies is more favourable in primiparae aged 35 or over.

Pregnancy outcome in primiparae of advanced maternal age.

OBJECTIVE: To investigate the impact of maternal age on singleton pregnancy outcome, taking into account intermediate and confounding factors. STUDY DESIGN: In this population-based retrospective cohort study, perinatal data of primiparous women aged 35 years or more (n = 2970), giving birth to a singleton child of at least 500 g, were compared to data of primiparous women aged 25-29 years old (n = 23,921). Univariate analysis was used to assess the effect of maternal age on pregnancy outcomes. The effects of intermediate (hypertension, diabetes and assisted conception) and confounding factors (level of education) were assessed through multivariable logistic regression analysis. RESULTS: Older maternal age correlated, independently of confounding and intermediate factors, with very preterm birth (gestational age <32 weeks) [adjusted odds ratio (AOR) 1.51, 95% confidence intervals (CI) 1.04-2.19], low birth weight (birth weight <2500 g) (AOR 1.69, 95% CI 1.47-1.94) and perinatal death (AOR 1.68, 95% CI 1.06-2.65). CONCLUSION: Maternal age is an important and independent risk factor for adverse pregnancy outcome.

Does practice make perfect? An age-matched study on grand multiparity in Flanders, Belgium.

AIM: To compare the perinatal outcome of grand multi-parous women (giving birth for the fifth to ninth time) and pauciparous (parity 2 to 4) women in the region of Flanders, Belgium. METHODS: Population-based, retrospective, age-matched study. RESULTS: 2832 grand multiparous women were compared with 2832 pauciparous women. In univariate analysis grand multiparous women showed more transverse lie, macrosomia, and fetal death and had less frequently epidural analgesia and episiotomy. Logistic regression demonstrated that grand multiparity was a significant factor contributing to fetal death and macrosomia. CONCLUSION: Grand multiparity is associated with fetal death and macrosomia in the region of Flanders, Belgium.

Perinatal outcome of 12,021 singleton and 3108 twin births after non-IVF-assisted reproduction: a cohort study.

Perinatal outcome of pregnancies caused by assisted reproduction technique (ART) is substantially worse when compared with pregnancies following natural conception. We investigated the possible risks of non-IVF ART on perinatal health. We conducted a retrospective cohort study with two exposure groups: a study group of pregnancies after controlled ovarian stimulation (COS), with or without artificial insemination (AI), and a naturally conceived comparison group. We used the data from the regional registry of all hospital deliveries in the Dutch-speaking part of Belgium during the period from January 1993 until December 2003 to investigate differences in perinatal outcome of singleton and twin pregnancies. 12 021 singleton and 3108 twin births could be selected. Naturally conceived subjects were matched for maternal age, parity, fetal sex and year of birth. The main outcome measures were duration of pregnancy, birth weight, perinatal morbidity and perinatal mortality. Our overall results showed a significantly higher incidence of prematurity (<32 and <37 weeks), low and very low birth weight, transfer to the neonatal intensive care unit and most neonatal morbidity parameters for COS/AI singletons. Twin pregnancies resulting from COS/AI showed an increased rate of neonatal mortality, assisted ventilation and respiratory distress syndrome. After excluding same-sex twin sets, COS/AI twin pregnancies were at increased risk for extreme prematurity and very low birth weight. In conclusion, COS/AI singleton and twin pregnancies are significantly disadvantaged compared to naturally conceived children.

Perinatal outcome of ICSI pregnancies compared with a matched group of natural conception pregnancies in Flanders (Belgium): a cohort study.

A retrospective cohort study was conducted with an intracytoplasmic sperm injection (ICSI) group and a naturally conceived comparison group. A total of 1655 singleton and 1102 twin ICSI births were studied with regard to perinatal outcome. Control subjects (naturally conceived pregnancies) were selected from a regional registry and were matched for maternal age, parity, place of delivery, year of birth and fetal sex. The main outcome measures were duration of pregnancy, birth weight, Apgar score <5 after 5 min, neonatal complications, perinatal death and congenital malformations. Twin births, when compared with singletons, carry a much higher risk of poor perinatal outcome. For both ICSI singletons and ICSI twins, no significant difference was found between ICSI and naturally conceived pregnancies for all investigated parameters. After excluding like-sex twin pairs, ICSI twin pregnancies were at increased risk for perinatal mortality (OR = 2.74, CI = 1.26-5.98), prematurity (OR = 1.38, CI = 1.10-1.75) and low birth weight (OR = 1.34, CI = 1.06-1.69) compared with spontaneously conceived different-sex twin pairs. In conclusion, the perinatal outcome of ICSI singleton and twin pregnancies was very similar to that of spontaneously conceived pregnancies in this large cohort study. After excluding like-sex twin pairs, ICSI twins were at increased risk for prematurity, low birth weight and higher perinatal mortality compared with the natural conception comparison group.

Obstetric and perinatal outcome of 1655 ICSI and 3974 IVF singleton and 1102 ICSI and 2901 IVF twin births: a comparative analysis.

A total of 3974 IVF and 1655 ICSI singleton births and 2901 IVF and 1102 ICSI twin births were evaluated. Pregnancies after both fresh and frozen transfers were included. IVF and ICSI singleton pregnancies were very similar for most obstetric and perinatal variables. The only significant difference was a higher risk for prematurity (< 37 weeks of amenorrhoea) in IVF pregnancies compared with ICSI pregnancies (12.4 versus 9.2%, OR = 1.39, 95% CI = 1.15-1.70). For twin pregnancies, differences were not statistically different except for a higher incidence of stillbirths in the ICSI group (2.08 versus 1.03%, OR = 2.04, 95% CI = 1.14-3.64). Intrauterine growth retardation with or without pregnancy-induced hypertension was observed more often in the ICSI group. Regression analysis of the data with correction for parity and female age showed similar results for twins. For singletons, this analysis showed similar results with the exception of low birth weight babies (< 2500 g), which were also observed more often in IVF pregnancies (9.6 versus 7.9%, OR = 0.79, CI = 0.65-0.98, P = 0.03). This large case-comparative retrospective analysis showed that the obstetric outcome and perinatal health of IVF and ICSI pregnancies is comparable.

Social inequalities in perinatal and infant mortality in the northern region of Belgium (the Flanders).

BACKGROUND: The study was intended to analyse the independent effect of some facets of the socio-economic status of both parents on perinatal, neonatal and post-neonatal mortality in the northern region of Belgium (the Flanders). METHOD: Perinatal data collected by the Study Centre for Perinatal Epidemiology were linked with socio-economic data collected by the district council. Mothers aged > or =25 years are included in the study. RESULTS: 50796 births were analysed. 452 infants died either before birth or during the first year of life. 52% of the foeto-infantile mortality occurred before birth and 57% of the infant mortality in the first week of life. The educational level was strongly related to foetal (p<0.001) and, to a lesser degree, to early-neonatal mortality (p=0.001). Employment did not correlate with any mortality item. Except for foetal mortality, the strongest correlation was always observed for maternal rather than paternal social items. In a logistic regression model, foetal mortality, perinatal mortality and infantile mortality remained strongly correlated with the educational level of the mother. Infant mortality beyond the first week of life was not correlated with any aspect of the social status of the parents. CONCLUSIONS: The educational level of the mother is the single most important determinant of infantile mortality in the Flanders representing the totality of hospital births by mothers aged > or =25 years in 1999 in the Flanders. STUDY QUESTION: Does education, profession and actual employment of both parents, independently operates discrimination in the outcome of pregnancy up to one year? Results: Maternal education is the only significant and independent determinant of foetal as well as neonatal and foeto-infantile mortality. Results: The status of the mother is by far more important than that of the father in determining the outcome of pregnancy.

Multiple gestation and infertility treatment: registration, reflection and reaction--the Belgian project.

Multiple pregnancies associated with infertility treatment are recognized as an adverse outcome and are responsible for morbidity and mortality related to prematurity and very low birthweight population. Due to the epidemic of iatrogenic multiple births, the incidence of maternal, perinatal and childhood morbidity and mortality has increased. This results in a hidden healthcare cost of infertility therapy and this may lead to social and political concern. Reducing the number of embryos transferred and the use of natural cycle IVF will surely decrease the number of multiple gestations. Consequently, optimized cryopreservation programmes will be essential. For non-IVF hormonal stimulation, responsible for more than one-third of all multiple pregnancies after infertility treatment, a strict ovarian stimulation protocol aiming at mono-ovulation is crucial. Multifetal pregnancy reduction is an effective method to reduce high order multiplets but carries its own risk of medical and emotional complications. Excellent data collection of all infertility treatments is needed in our discussion with policy makers. The Belgian project, in which reimbursement of assisted reproduction technology-related laboratory activities is linked to a transfer policy aiming at substantial multiple pregnancy reduction, is a good example of cost-efficient health care through responsible, well considered clinical practice.

Screening for trisomy 21 in Flanders: a 10 years review of 40.490 pregnancies screened by maternal serum.

OBJECTIVE: To evaluate maternal serum screening for trisomy 21 (MSS) in Flanders between 1992 and 2002. STUDY DESIGN: Data of a large database on the results of MSS, nuchal translucency (NT) and pregnancy outcome were analysed retrospectively. RESULTS: Despite an excellent performance of second trimester MSS at a maternal age > or = 35 years (94.4% detection rate (DR) of trisomy 21 at a false positive rate (FPR) of 22.4%), the proportion of patients above 35 years of age in the study population was significantly lower than in the Flemish general pregnant population (5.5% versus 8.9%, P < 0.001). In the population screened by MSS and NT, the DR of second trimester MSS at a 5% FPR was 44.4%, which was lower than 66.6% in the population screened by MSS without NT. When nine trisomy 21-affected pregnancies were compared to 3265 normal pregnancies, the mean NT-MoM values were not significantly different (1.16 +/- 0.89 versus 1.00 +/- 0.46, P > 0.05). Both the findings comply to a sequential screening practice where second trimester MSS is only performed after a normal measurement of NT in the first trimester. CONCLUSION: In Flanders, the uptake of second trimester maternal serum screening is low in women aged 35 years or more. Its screening performance decreased after the introduction of sequential screening.

Unilateral posterior crossbite and chin deviation: is there a correlation?

A retrospective study evaluating the clinical discernment of chin deviations in general, and especially in relation to unilateral posterior crossbite (UPXB), was carried out to determine whether (1) there is a correlation between UPXB and clinically discernible chin deviation, (2) there are differences between the judgement of professional dental observers and laymen, (3) visual assessment of chin deviation compares well with computer-assisted assessment and (4) how large a chin deviation should be before it is noticed. The experimental group consisted of 72 patients (30 males and 42 females, average age 14.5 years) with a UPXB. A control group of 72 subjects without a UPXB was matched for age and sex. In addition, one computer-designed face was added with chin deviations of 0, 2, 4, 6 and 8 mm to the left. The full-face slides of all subjects were shown twice, with an interval of 2 weeks, to an audience of seven orthodontists, ten dental students and five laymen judging by eye. A computer-assisted assessment was carried out by one observer, in order to create a standardized comparison to visual scoring. Inter-observer examination of visual scoring showed moderate agreement (kappa = 0.48). When comparing the computer-assisted and visual scores, the intra-class correlation coefficient (ICC) was 0.87. There were no major differences between professional observers and laymen, although the latter gave significantly more responses in the direction opposite to the crossbite. In 70.3 per cent (on average) of the subjects with a crossbite, a deviation in the same direction as the crossbite was noticed visually. The majority of the observers observed a chin deviation of at least 4 mm.

Has hypodontia increased in Caucasians during the 20th century? A meta-analysis.

It has been claimed that agenesis of permanent teeth has increased over the years. The present study tested this hypothesis in Caucasians. Published data on the prevalence of children with one or more congenitally missing permanent teeth were selected on the basis of strictly imposed criteria. Using a meta-analysis, the data were evaluated and presented chronologically. Furthermore, the selected publications were checked for differences in the prevalence of agenesis between the male and female populations. Finally, information on the occurrence of upper and lower premolars as well as upper incisor agenesis was collected and calculated as a percentage of the total number of congenitally missing teeth. From 42 studies on this subject, 19 were selected based upon six stringently applied criteria. Chronological classification of the percentage of children with congenital absence of one or more permanent teeth revealed relatively higher percentages since 1957. Fourteen out of the selected studies presented data on sex distribution. In all but one publication girls tended to have a slightly higher occurrence of missing teeth compared with boys of the same age. The second lower premolars were most often agenetic, whereas missing upper laterals occurred almost equally as agenesis of the upper second premolars. The considered period of time is too short and the available data too limited to describe a possible trend in the human dentition. However, this meta-analysis seems to confirm that hypodontia has been diagnosed more often in recent studies.

Flemish obstetricians' personal preference regarding mode of delivery and attitude towards caesarean section on demand.

OBJECTIVES: To assess Flemish obstetricians' preferences about mode of delivery for themselves or their partners and to determine the frequency of caesarean section on demand in Flanders. STUDY DESIGN: A structured anonymous postal questionnaire was sent to all 672 registered gynaecologist-obstetricians in Flanders. RESULTS: The response rate was 44%. In the case of an uncomplicated singleton first pregnancy with a cephalic presentation 2% preferred elective caesarean section. There was no difference between male and female obstetricians. Seventy percent said that they would never perform caesarean section on demand. At least 2.6% of all caesarean sections in Flanders seems to be performed on patient's demand. CONCLUSION: The attitude of Flemish gynaecologist-obstetricians is clearly in favour of vaginal delivery both for themselves, their partners and their patients.

A matched cohort comparison of the outcome of twin versus singleton pregnancies in Flanders, Belgium.

To compare perinatal outcome of singleton versus twin pregnancies a matched cohort study was performed in Flanders, Belgium. All twins delivered in the region of Flanders during 1998-1999 were compared to singletons, matched for gestational age, fetal sex and maternal parity, resulting in 4384 infants in each group. Above 32 weeks of gestation, birthweight was significantly lower in twins (2095 +/- 364 g versus 2315 +/- 523 g; p < 0.001, 95% confidence interval 193 to 246 g). Perinatal mortality was also significantly lower in twins (1.98% versus 1.26%; odds ratio for twins 0.63; 95% confidence interval 0.53-0.75; p < 0.001 ), this was mostly due to fetal and not to early neonatal mortality. Congenital malformations occurred less frequently in twins (2.5% versus 3.7%; odds ratio for twins 0.80, 95% confidence interval 0.69-0.92; p = 0.001). From gestational age of 32 weeks on, respiratory distress syndrome was less frequent in twins (6.7% versus 8.0%; odds ratio for twins 0.81; 95% confidence interval 0.68-0.97; p = 0.011 ). No significant differences were noted with regard to intraventricular haemorrhage, neonatal infections and retinopathy of prematurity. Although twins have a lower birthweight, their outcome is more favorable compared to singletons, when matched for gestational age.