Nonmigrants

The KiGGS survey is based on a nationally representative sample of children and adolescents 0–17 years of age with main residence in Germany. The sampling procedure was based on a two-stage protocol developed in co-operation with the Centre for Survey Research and Methodology (ZUMA), Mannheim, Germany. The study was approved by the Charité/Universitätsmedizin Berlin ethics committee and the Federal Office for the Protection of Data.
First, a systematic sample of 167 primary sample units (PSUs) was drawn from an inventory of German communities stratified according to the BIK classification system [2 ], which measures the grade of urbanization, and the geographic distribution. The number of PSUs per strata was determined using the Cox procedure for community sampling [3 (link)] with sampling probability proportional to population size. In order to ensure sufficient sample size for analyses stratifying according to residence in former East or West Germany, a disproportionate number of PSUs was included to represent former West (n = 112) and East (n = 50) Germany, and the city of Berlin (n = 5). At the second stage, an equal number of addresses (n = 24) per birth cohort were randomly selected (simple random sample) from local population registries within selected PSUs 8 weeks prior to the start of examinations. A final simple random sample was drawn at the Robert Koch Institute, including a total of 8, 9 or 10 children and adolescents per birth cohort, depending on community size. Thus, the target population per PSU consisted of 144, 162 or 180 persons eligible to be contacted and invited to participate in the study. Oversampling of children and adolescents from families with a migration nationality was used, as we expected a higher proportion of undeliverable contacts and non-respondents in this subgroup compared to children and youths from non-migrant families. The total KiGGS sample included 28,299 children and adolescents.

We recruited women delivering in three secondary and tertiary care maternity hospitals of Berlin/Germany ((1) the Virchow Campus site of the Charité University Hospital, (2) the Vivantes Klinikum am Urban, and (3) the Vivantes Klinikum Neukölln) in a 12-month period 2011/12 (n = 8157). Minors (n = 105, 1.3%), tourists not resident in Germany (n = 24, 0.3%), women terminating a pregnancy, and women with miscarriages and stillbirths (fetal death in utero ascertained at hospital admission and before onset of labor, n = 106, 1.3%) were excluded. It was not possible to contact 363 women despite multiple attempts. Of the remaining 7559 women 381 declined to participate. We conducted face-to-face interviews and linked them with highly standardized obstetric process and outcome data from hospital databases. Linkage of available interview data with obstetric process and outcome data failed in 72 cases. Six women did not consent to the linkage of data sources. In total, 7100 women participated (response rate of 89.6%). This corresponded to 7334 birth data records because of twin and triplet births.
For the analysis presented here, we considered only nulliparous women with vertex pregnancies and singleton birth, 37th week of gestation onwards. Women with elective cesarean delivery were excluded as they are not informative for our study question. We further restricted the sample to women with own migration experience (1st generation immigrants). Migrant women are a heterogeneous group. Health differences in this group might be larger than between migrant and non-migrant women. For this reason we selected women originating from Turkey and Lebanon (the two largest and only immigrant groups that allow separate analysis) and to women without a migration history (non-immigrant women). Also, 63 women without data on cervical dilatation were removed from analyses (see Fig. 1).Fig. 1

Flowchart of case recruitment, Berlin Perinatal study, 2011/12

In the original study, interviews were conducted with each subject at two time points: on admission to the delivery room (T1) and on the second or third day postpartum in the maternity wards (T2). Questionnaires were available in German, Turkish, Kurdish, Arabic, and other languages. Translators were involved in case of language barriers. Nearly all women with migration background (193 of 205) were able to communicate with the obstetrician in German. For this analysis, only T1 data was used. Formally, the analyses reported here are secondary analyses as the original study question related to pregnancy outcomes such as frequeny of cesarean deliveries [20 (link)].

One hundred and thirty-nine skulls constituted the migrant sample, recovered from the shipwreck of 18 April 2015 in the Mediterranean Sea and housed at the Laboratory of Forensic Anthropology and Odontology (LABANOF) for identification purposes. They are currently being examined from a genetic and anthropological perspective for the best possible biological profile to be completed for comparison with future antemortem data [33 ]. Migratory status of these individuals is demonstrated by the context of retrieval. Among the remains in various stages of decomposition, many skeletonized remains were found commingled; the skulls selected are part of these commingled remains [31 (link)]. Sometimes, the crania were found anatomically connected to their respective mandibles. While sex estimations relied upon standard morphological features [34 (link)], age-at-death was estimated considering skeletal methods, with the spheno occipital and palatal sutures [35 (link)], and dental methods based on the state of eruption and development, translucency of the tooth root and periodontosis, and dental pulp regression, observed macroscopically or through X-rays [36 (link),37 (link),38 (link),39 (link),40 (link),41 (link)]. Further details are currently in the process of publication in institutional and scientific reports. Population affinity was performed based on morphological features of the cranium [42 ]. This method gives probabilities associated to four macro-categories of ancestry: African, American Indian, Asian, and European. The results showed that all crania belonged to male individuals aged between 16 and 35 years, and mainly of African origin [33 ]. It is important to mention that their “migrant” status was not estimated but already known from the context of the shipwreck. While their exact reason for migrating is not known, “there is no doubt that any person making the decision to cross the Mediterranean at the risk of his or her life has imperative reasons to do so” [43 ].
Twenty-five skulls were selected from the CAL Milano Cemetery Skeletal Collection to serve as control sample. This skeletal collection, started in 2012, is composed of unclaimed remains buried in Milanese cemetery and housed at the LABANOF [32 (link)]. In addition to being contemporary (with individuals who died in the 20th century, including 80% after 1980), the collection has the advantage of being documented, meaning that the individuals are associated to a documentation that includes sex, age-at-death, date of birth, date of death, cause of death, and pathological conditions related to it. The individuals of the CAL Milano Cemetery Skeletal Collection were primarily selected based on their ages-at-death, in order to correspond to the same age range as that of the migrants, that is, between 20 and 35 years. From this criterion, a total of 28 individuals were found in the collection. However, this young age-at-death requirement created a selective mortality bias in the sample which was considered. The non-migrant sample was therefore clearly contextualized and the limitations in inferences were clearly set in order to deal with this selectivity bias. The second selection criterion was the good preservation of the remains, specifically of the cranium and mandible; only skeletons for which the three stress markers selected could be potentially observable (i.e., preservation of the orbits and cranial vault, presence of at least half of the dentition) were selected, which resulted in the removal of three cases from the sample. These two criteria of selection (age-at-death and preservation) thus resulted in a sample constituted of 19 males and 6 females, all of Italian descent. Biological profile was only estimated for the migrant sample, since this data was already known for the cemetery sample.

A statistical study was realized to compare the presence and severity of the stress markers in both samples. Shapiro–Wilk tests were performed with R (own scripts were written) to verify the normality of the samples and decide whether to use parametric or non-parametric tests for their analysis. Regarding the presence of stress markers and their relationship with the sample, Pearson’s Chi-squared tests of independence were performed with R (own scripts were written) to assess the relationship of the variables “CO”, “PH”, and “LEH” to the sample of migrants.
Among the migrant group, severity of lesions was evaluated on a subsample of 25 skulls. Wilcoxon signed-rank tests, realized on R (own scripts were written), were applied to the scores of severity of CO and PH to compare their values and assess whether there was a significative difference in severity of the lesions between the migrant and non-migrant samples and in which sample the lesions were more severe. Results were considered significant at p ≤ 0.05.