Miranda Tromp

Travel time from home to hospital and adverse perinatal outcomes in women at term in the Netherlands

Please cite this paper as: Ravelli A, Jager K, de Groot M, Erwich J, Rijninks‐van Driel G, Tromp M, Eskes M, Abu‐Hanna A, Mol B. Travel time from home to hospital and adverse perinatal outcomes in women at term in the Netherlands. BJOG 2011;118:457–465.

Results from simulated data sets: probabilistic record linkage outperforms deterministic record linkage

OBJECTIVE To gain insight into the performance of deterministic record linkage (DRL) vs. probabilistic record linkage (PRL) strategies under different conditions by varying the frequency of registration errors and the amount of discriminating power. STUDY DESIGN AND SETTING A simulation study in which data characteristics were varied to create a range of realistic linkage scenarios. For each scenario, we compared the number of misclassifications (number of false nonlinks and false links) made by the different linking strategies: deterministic full, deterministic N-1, and probabilistic. RESULTS The full deterministic strategy produced the lowest number of false positive links but at the expense of missing considerable numbers of matches dependent on the error rate of the linking variables. The probabilistic strategy outperformed the deterministic strategy (full or N-1) across all scenarios. A deterministic strategy can match the performance of a probabilistic approach providing that the decision about which disagreements should be tolerated is made correctly. This requires a priori knowledge about the quality of all linking variables, whereas this information is inherently generated by a probabilistic strategy. CONCLUSION PRL is more flexible and provides data about the quality of the linkage process that in turn can minimize the degree of linking errors, given the data provided.

Regional perinatal mortality differences in the Netherlands; care is the question

BackgroundPerinatal mortality is an important indicator of health. European comparisons of perinatal mortality show an unfavourable position for the Netherlands. Our objective was to study regional variation in perinatal mortality within the Netherlands and to identify possible explanatory factors for the found differences.MethodsOur study population comprised of all singleton births (904,003) derived from the Netherlands Perinatal Registry for the period 2000–2004. Perinatal mortality including stillbirth from 22+0 weeks gestation and early neonatal death (0–6 days) was our main outcome measure. Differences in perinatal mortality were calculated between 4 distinct geographical regions North-East-South-West. We tried to explain regional differences by adjustment for the demographic factors maternal age, parity and ethnicity and by socio-economic status and urbanisation degree using logistic modelling. In addition, regional differences in mode of delivery and risk selection were analysed as health care factors. Finally, perinatal mortality was analysed among five distinct clinical risk groups based on the mediating risk factors gestational age and congenital anomalies.ResultsOverall perinatal mortality was 10.1 per 1,000 total births over the period 2000–2004. Perinatal mortality was elevated in the northern region (11.2 per 1,000 total births). Perinatal mortality in the eastern, western and southern region was 10.2, 10.1 and 9.6 per 1,000 total births respectively. Adjustment for demographic factors increased the perinatal mortality risk in the northern region (odds ratio 1.20, 95% CI 1.12–1.28, compared to reference western region), subsequent adjustment for socio-economic status and urbanisation explained a small part of the elevated risk (odds ratio 1.11, 95% CI 1.03–1.20). Risk group analysis showed that regional differences were absent among very preterm births (22+0 – 25+6 weeks gestation) and most prominent among births from 32+0 gestation weeks onwards and among children with severe congenital anomalies. Among term births (≥ 37+0 weeks) regional mortality differences were largest for births in women transferred from low to high risk during delivery.ConclusionRegional differences in perinatal mortality exist in the Netherlands. These differences could not be explained by demographic or socio-economic factors, however clinical risk group analysis showed indications for a role of health care factors.

Decreasing perinatal mortality in The Netherlands, 2000–2006: a record linkage study

Background: The European PERISTAT-1 study showed that, in 1999, perinatal mortality, especially fetal mortality, was substantially higher in The Netherlands than in other European countries. The aim of this study was to analyse the recent trend in Dutch perinatal mortality and the influence of risk factors. Methods: A nationwide retrospective cohort study of 1 246 440 singleton births in 2000–2006 in The Netherlands. The source data were available from three linked registries: the midwifery registry, the obstetrics registry and the neonatology/paediatrics registry. The outcome measure was perinatal mortality (fetal and early neonatal mortality). The trend was studied with and without risk adjustment. Five clinical distinct groups with different perinatal mortality risks were used to gain further insight. Results: Perinatal mortality among singletons declined from 10.5 to 9.1 per 1000 total births in the period 2000–2006. This trend remained significant after full adjustment (odds ratio 0.97; 95% CI 0.96 to 0.98) and was present in both fetal and neonatal mortality. The decline was most prominent among births complicated by congenital anomalies, among premature births (32.0–36.6 weeks) and among term births. Home births showed the lowest mortality risk. Conclusions: Dutch perinatal mortality declined steadily over this period, which could not be explained by changes in known risk factors including high maternal age and non-western ethnicity. The decline was present in all risk groups except in very premature births. The mortality level is still high compared with European standards.

Anonymous non‐response analysis in the ABCD cohort study enabled by probabilistic record linkage

Selective non-response is an important threat to study validity as it can lead to selection bias. The Amsterdam Born Children and their Development study (ABCD-study) is a large cohort study addressing the relationship between life style, psychological conditions, nutrition and sociodemographic background of pregnant women and their childrens health. Possible selective non-response and selection bias in the ABCD-study were analysed using national perinatal registry data. ABCD-study data were linked with national perinatal registry data by probabilistic medical record linkage techniques. Differences in the prevalence of relevant risk factors (sociodemographic and care-related factors) and birth outcomes between respondents and non-respondents were tested using Pearson chi-squared tests. Selection bias (i.e. bias in the association between risk factors and specific outcomes) was analysed by regression analysis with and without adjustment for participation status. The ABCD non-respondents were significantly younger, more often non-western, and more often multiparae. Non-respondents entered antenatal care later, were more often under supervision of an obstetrician and had a spontaneous delivery more often. Non-response however, was not significantly associated with preterm birth (odds ratio 1.10; 95% CI 0.93, 1.29) or low birthweight (odds ratio 1.16; 95% CI 0.98, 1.37) after adjustment for sociodemographic risk factors. The associations found between risk factors and adverse pregnancy outcomes were similar for respondents and non-respondents. Anonymised record linkage of cohort study data with national registry data indicated that selective non-response was present in the ABCD-study, but selection bias was acceptably low and did not influence the main study questions.

Ignoring Dependency between Linking Variables and Its Impact on the Outcome of Probabilistic Record Linkage Studies

OBJECTIVES This study sought to examine the differences between ignoring (naïve) and incorporating dependency (nonnaïve) among linkage variables on the outcome of a probabilistic record linkage study. DESIGN AND MEASUREMENTS We used the outcomes of a previously developed probabilistic linkage procedure for different registries in perinatal care assuming independence among linkage variables. We estimated the impact of ignoring dependency by re-estimating the linkage weights after constructing a variable that combines the outcomes of the comparison of 2 correlated linking variables. The results of the original naïve and the new nonnaïve strategy were systematically compared for 3 scenarios: the empirical dataset using 9 variables, the empirical dataset using 5 variables, and a simulated dataset using 5 variables. RESULTS The linking weight for agreement on 2 correlated variables among nonmatches was estimated considerably higher in the naïve strategy than in the nonnaïve strategy (16.87 vs. 13.55). Therefore, ignoring dependency overestimates the amount of identifying information if both correlated variables agree. The impact on the number of pairs that was classified differently with both approaches was modest in the situation in which there were many different linking variables but grew substantially with fewer variables. The simulation study confirmed the results of the empirical study and suggests that the number of misclassifications can increase substantially by ignoring dependency under less favorable linking conditions. CONCLUSION Dependency often exists between linking variables and has the potential to bias the outcome of a linkage study. The nonnaïve approach is a straightforward method for creating linking weights that accommodate dependency. The impact on the number of misclassifications depends on the quality and number of linking variables relative to the number of correlated linking variables.

Increasing maternal age at first pregnancy planning: health outcomes and associated costs

Objectives To describe the consequences in terms of health outcomes, care and associated healthcare costs for three hypothetical cohorts of women planning their first pregnancy at a fixed, different age. Design Decision model based on data from perinatal registries and the literature. Setting The Netherlands. Population 3 hypothetical cohorts of 100 000 women aged 23, 29 and 36 years, planning a first pregnancy. Main outcome measures Live birth, pregnancy complications for mother and child and associated healthcare costs. Results For the three cohorts of 23-, 29- and 36-year-old women, 1.6%, 4.6% and 14% of women would not succeed in an ongoing pregnancy (spontaneous or after assisted reproductive technology). The cohort aged 36 gave 9% more miscarriages, 8% more fertility treatment and 1.4% more multiple births than the cohort aged 29. The proportion of caesarean sections among low risk women was 4.9% and 11% higher respectively for the cohorts aged 29 and 36, compared with the cohort aged 23 at start. Eventually, 98%, 95% and 85% of the women in each of the three cohorts gave live birth. The costs for the two older cohorts were €415 and €1662 higher per ongoing pregnancy than the cohort aged 23 years. Conclusions Spontaneous conception and mode of delivery are most susceptible to increasing maternal age leading to involuntary childlessness and non-spontaneous labour. The increase in assisted reproduction technology, twin pregnancies and delivery complications results in higher costs along with fewer ongoing pregnancies at higher age.