Background: Following the Thalidomide disaster, the Medical Birth Registry of Norway (MBRN) was established in 1967, with epidemiological surveillance of congenital anomalies as one main aim. Limb reduction defects (LRD) constitute a rare and heterogeneous anomaly group, where correct registration and classification is important for surveillance and research. We aimed at reviewing and recoding LRD cases in the MBRN using the same classification system for all years, and evaluate time trends, characteristics and risk factors, 1970–2016. Methods: After reviewing and recoding LRD cases using International Classification of Diseases (ICD), 10th version, for all years, time trends, association with major anomalies, risk factors and infant outcomes were calculated. Generalized linear models for the binomial family with log link gave relative risks (RR) with 95% confidence intervals (CI). Classification of LRD as suggested by European surveillance of congenital anomalies (EUROCAT) was attempted. Results: Overall LRD prevalence, 1970–2016, was 4.4 per 10 000, slightly increasing during 1970–1981, followed by relatively stable rates. There were more defects in upper than lower limbs. Defects in hands/fingers were most common, but unspecific descriptions prevented classification of LRD according to EUROCAT. A majority of cases had associated anomalies, the most common being other limb defects, followed by cardiac defects and anomalies in the nervous and digestive systems. From 1999, 26% of LRD cases were terminated, more than 90% of these had associated major anomalies. Stillbirth, neonatal and infant mortality were higher among infants with LRD, also related to associated anomalies. Pre-gestational diabetes was associated with a more than three times increased risk of offspring total LRD, while no association with maternal epilepsy was found. Taking folate/multivitamin supplements before and/or during pregnancy was associated with lower risk of offspring LRD (adjusted RR 0.7; 95% CI 0.6–0.9), while daily smoking did not significantly increase the risk. Conclusion: The MBRN now has information on LRD coded by ICD-10 from 1970, but information is not specific enough to use other recommended classification systems. Collecting radiographic descriptions and/or more details from hospital records would improve the quality of the registry data. Taking folate supplements before/during pregnancy may reduce the risk of offspring LRD.
Keywords: Research Article; Medicine and health sciences; Congenital disorders; Congenital anomalies; Biology and life sciences; Anatomy; Musculoskeletal system; Body limbs; Endocrinology; Endocrine disorders; Diabetes mellitus; Metabolic disorders; Women's health; Obstetrics and gynecology; Stillbirths; Neurology; Epilepsy; Arms; Hands; Birth defects; Limb reduction defects; Developmental biology; Morphogenesis; People and places; Population groupings; Age groups; Children; Infants; Families
In the late 1950'ies, Thalidomide was released as a sedative and antiemetic drug, marketed for treating morning sickness in pregnant women. By 1962, it was withdrawn from use over most of the world after having caused congenital anomalies, especially limb reduction defects (LRD), in more than 10 000 children globally [[
From 1967 to 1998, births were notified to the MBRN using a standard paper notification form, where health information, including offspring congenital anomalies, was notified as free text descriptions. Free text was coded at the registry using the International Classification of Diseases (ICD), version 8 (ICD-8), and internal codes if needed. LRD cases were coded by ICD-8 during the years 1967–1987, with codes for reduction defect upper limb, lower limb and unspecified limb, and by internal codes during 1988–1998. The internal codes specified transverse, preaxial, postaxial, and intercalary reduction defects, but unfortunately without separating defects in upper and lower limbs. In 1999, the MBRN switched from ICD-8 to ICD-10, with the British Paediatric Association's supplement (ICD-10-BPA), for coding congenital anomalies. LRD codes are here much more detailed than in ICD-8.
The previous National Resource Centre for Dysmelia (closed in 2014, activities continued in the National Professional Network for Dysmelia, Norwegian National Advisory Unit on Rare Disorders TRS) had as one of its mandates to build a knowledge base for patients with congenital upper and lower limb anomalies (CULA/CLLA), where LRD constitute an important subgroup. The centre has supported the MBRN in its quality work on LRD, enabling the registry to review all cases registered from 1970 to 1998 and recode these using ICD-10. Since this version of the ICD is more detailed than ICD-8 and defects in upper and lower limbs are separated, the quality of LRD registration could be improved. The overall aim of the collaboration was that the MBRN after the recoding would provide a better basis for research on these rare congenital anomalies.
This paper describes the results of the recoding, and evaluates the recoded data by describing the distribution and time trends for the different reduction defects, their associated anomalies, relations of LRD with mortality and certain risk factors, while comparing the results with the literature.
The MBRN is based on mandatory notification of all births in the country, including stillbirths and late fetal deaths from 16 weeks of gestation [[
LRD prevalence per 10 000 births in the MBRN based on the original registered codes (ICD-8 and internal codes) showed an evident increase over time, especially for boys, until 1998, and then a marked drop (overall trends shown in Fig 1, "old codes"). The drop in 1999 coincides with the mentioned additions in the MBRN (NICU notifications and TOPFA reports), which have generally led to a better ascertainment of congenital anomalies and therefore an increase in prevalence for most anomalies from 1999. The time trends in "old codes" shown in Fig 1 showed the opposite pattern and underlined the need to re-evaluate the coding of LRD in the MBRN for the years before 1999.
All paper birth notifications from 1970 to 1998 where infants were registered with LRD were collected from storage, reviewed and recoded to ICD-10 by two medical doctors at the MBRN (KK and TN) on the basis of free text descriptions on the forms. When descriptions were unspecific or unclear, the cases were discussed with a paediatric orthopedic surgeon (TSK or SS). Results of the recoded data were then analysed using anonymous data files. The legal basis for this quality assurance project was the Medical birth registry regulation (
We aimed at using the guide "Description and classification of congenital limb defects" by Stoll et al [[
Table 1: Guide to description and classification of congenital limb defects [
Group Subgroups Suggested ICD-10 codes Terminal Transverse Defects: Absence of distal structure of the limb with proximal structures more or less normal Amelia–total absence of the extremities Q710, Q720, Q730 Hemimelia–total absence of forearm and hand or of foreleg and foot Q712, Q722 Acheiria–absence of hand Q713 Apodia–absence of foot Q723 Adactyly–absence of digits Q713, Q723 Ectrodactyly–total or partial absence of phalanx Q713, Q723 Proximal-intercalary Defect: Absence or severe hypoplasia of proximal-intercalary part of the limb when the distal structures (ie. the digits), whether normal or malformed, are present: Absence of humerus and/or radius and ulna (with hand normal or near normal) Q711 Absence of femur and/or tibia and fibula (with foot normal or near normal). Q721, Q724 Longitudinal Defects: Absence or severe hypoplasia of lateral part of the limb: Preaxial (Radial-tibial)–absence or severe hypoplasia of preaxial structures of the limb (thumb, first metacarpal, radius: hallux, first metacarpal, tibia). Q714, Q725 Postaxial (Ulna-fibula)–absence or severe hypoplasia of postaxial structures of the limb (little finger, 5th metacarpal, ulna; 5th toe, 5th metatarsal, fibula). Q715, Q726 Split Hand-foot: Absence of central digits with or without absence of central metacarpal/ metatarsal bones usually associated with syndactyly of other digits. Typical split hand/foot: cone-shaped cleft tapering proximally and dividing the hand into 2 parts, which can be opposed like lobster-claws. In the mildest forms the 3rd digit (middle finger or 3rd tow) is absent but the corresponding metacarpal/ metatarsal bone is almost normal. Q716, Q727 Monodactyly of the hand is characterised by deficiency of the central and radial digits, such that there is no cleft formation and only one digit is present (usually the 5th). Q716, Q727 Multiple Types of Reduction Defects: Infants with more than one type of reduction according to the classification given above.
After recoding, we evaluated results by analysing time trends of LRD prevalence per 10 000 births from 1970–2016, overall and for upper, lower and unspecified limb, and we calculated the frequency of specific diagnoses. We also described associated major congenital anomalies during 1970–1998 and 1999–2016, overall and for TOPFA cases, stillbirths and neonatal deaths from 1999. We evaluated some potential risk factors for offspring LRD, such as maternal age and parity as well as maternal pre-gestational diabetes, maternal epilepsy and, from 1999, smoking habits and use of folate/multivitamin supplements. Finally, stillbirth rates (per 1000 births), neonatal mortality and infant mortality (per 1000 live births) among LRD cases with and without associated anomalies were compared with rates in infants without LRD. We also compared low birth weight (LBW, birth weight < 2500 grams), preterm delivery (< 37 completed weeks of gestation) and male sex among cases with and without LRD.
We used frequency tables and generalized linear models for the binomial family with log link to estimate crude and adjusted relative risks (RR) with 95% confidence intervals (CI). Time trends were judged by evaluating linear trends in the multivariate models. The following variables were evaluated as possible confounding factors (varying depending on the specific analysis, see table footnotes): year of birth (four-year groups), maternal age (<20, 20–24, 25–29, 30–34, 35–39, 40+ years), maternal pre-gestational diabetes (yes/no), sex, and for data from 1999: smoking habits (daily smoking yes/no), and use of folate/multivitamin supplements (yes/no). There were 19% missing in the smoking variable, and 12% missing in the folate/multivitamin variable, however, these were not missing at random as the TOPFAs had 91% missing for smoking and 45% missing for folate/multivitamins. Information on maternal chronic diseases was also missing for most TOPFAs. When analysing the associations of maternal diabetes, epilepsy, smoking and folate/multivitamin supplements with LRD, we therefore excluded TOPFAs. We then used multiple imputation with chained equations and 20 imputations to impute missing data in smoking and folate/multivitamins. Variables used in the imputation were the model variables and mother's marital status, birth year, mother's birth year, birth weight, gestational age, perinatal death, preeclampsia, use of assisted reproduction technology, all significantly associated with smoking and folate/multivitamin supplements. Two-sided tests with a significance threshold of P<0.05 were used in all analyses. We used SPSS version 25 (IBM Statistical Package for the Social Sciences, SPSS Inc, Chicago, IL, USA) and STATA intercooled v.14 (StataCorp LP 2015. Stata Statistical Software: Release 14) for analyses.
The free text descriptions of congenital anomalies on the birth notification forms, 1970–1998, varied in detail and could be unspecific. For example, the free text "lacks one finger" could, depending on which finger, be recoded using Q713 (Congenital absence of hand and finger(s)), but also Q716 (Lobster-claw hand) if the missing finger was the third, Q714 (longitudinal reduction defect, radius) or Q715 (longitudinal reduction defect, ulna) if the first or fifth. Several cases had been coded with LRD codes, but where free text descriptions were not specific for a reduction defect. For most of these cases, we used other codes, e.g. "Deformed hand" which had been coded by ICD-8 code 7552 (reduction defect upper limb), was recoded using Q681 (Congenital deformity of hand). These situations were discussed with an orthopedic surgeon.
A total of 1 369 cases were registered with LRD in the MBRN from 1970 to 2016 before recoding. After recoding cases in 1970–1998, this number was reduced to 1 206. In the same period, a total of 2 745 119 births were registered in the MBRN, giving an LRD prevalence of 5.0 per 10 000 before recoding, and 4.4 per 10 000 afterwards. For 1970–1998, a total of 869 cases were registered with LRD before recoding (5.2 per 10 000), which was reduced to 706 (4.2 per 10 000) after recoding. During 1999–2016, the total number of registered LRD cases was 500 with prevalence 4.6 per 10 000, and the recoded data thus showed the expected increase in prevalence for the years 1999–2016 relative the years before.
In the last time period (1999–2016), 129 of the 500 LRD cases (25.8%) were TOPFAs, and 140 of 352 live born infants with LRD (39.8%) were transferred to a NICU after birth.
Time trends in prevalence of LRD per 10 000 births as registered in the MBRN before and after recoding are shown in Fig 1. After recoding, the increase in prevalence from 1970 to 1998 with the sudden decrease thereafter was no longer as evident as before. Over the full time period (1970–2016), there was a slight increase in recoded LRD prevalence (test for trend, P<0.01, Wald test), seemingly due to a statistically significant increase in the first decade with a marked high prevalence in 1981 (7.4 per 10 000). During 1982–2016, there was no statistically significant linear trend over time, (test for trend, P = 0.9, Wald test).
Among all 1 206 recoded LRD cases, 783 (64.9%) had defects registered in the upper limbs only, 249 (20.6%) in the lower limbs only and 102 (8.5%) in both upper and lower limbs. In 72 cases (6.0%), the affected limbs were not specified as being upper or lower. Fig 2 shows prevalence, 1970–2016, for defects in upper, lower and unspecified limb (those with both limbs affected shown twice). The prevalence of reduction defects in the upper limbs was slightly more than twice that in the lower limbs during the entire period, with overall prevalences being 3.2 and 1.3 per 10 000, respectively. For 86% of all cases, only one reduction defect was registered. The most common defect was Q713: "Congenital absence of hand and finger(s)", registered in 392 of the 1 206 cases (32.5%). The corresponding code in the lower limb, Q723: "Congenital absence of foot and toe(s)", was registered in 135 individuals (11.2%). "Congenital absence of both forearm and hand" (Q712) and "Longitudinal reduction defect of radius" (Q714) were both also relatively frequent, and registered in 10.5% and 11.8%, respectively, see S1 Table.
We had aimed at classifying the reduction defects using the classification system shown in Table 1, but due to unspecific descriptions of defects in the hands and feet where the exact finger(s) and toe(s) affected were often not specified, this proved impossible.
For LRD cases with associated major anomalies, there was a marked difference between the years before and after 1999: During 1970–1998, associated major anomalies were registered in 26.3%, while this increased to 53.2% in the following years (1999–2016). Fig 3 shows the distribution of associated anomalies (percent) for LRD cases in 1970–1998 and 1999–2016. In both periods, other limb anomalies dominated: 14.3% in the first time period and 26.6% in the last. Among these, syndactyly was the most frequent, 39% and 41% of the other limb anomalies in the first and last period, respectively, followed by club foot (pes equinovarus) with around 25% of other limb anomalies in both periods, while polydactyly was found in 5.0% (1970–1998) and 11.3% (1999–2016). From 1999, cardiac defects followed other limb defects in frequency (16.6% of the 500 LRD cases), then nervous system anomalies (13.6%) and anomalies of the digestive system (12.2%). Chromosomal syndromes were registered in 36 of the 500 LRD cases (7.2%) in the last time period, where 24 of 36 were trisomy 18. Before 1999, all other anomaly groups except other limb defects were rare, with nervous system anomalies being registered in 4.4%, cardiac defects in 2% and chromosomal syndromes in 0.8% of the LRD cases.
Among 207 cases with associated major anomalies outside limbs in 1999–2016, approximately one third (N = 71, 34%, or 14% of all 500 cases) were registered with acknowledged associations or syndromes (VACTERL association, sirenomelia, amniotic bands, limb-body-wall complex and teratogenic, genetic or chromosomal syndromes). The remaining 136 (27% of all 500 cases) were classified as non-syndromic multiple major anomalies. Among the 429 LRD cases without acknowledged associations or syndromes, the largest group of associated anomalies was cardiac defects (N = 53, 12.4%), followed by anomalies in the digestive and in the nervous system (both N = 40, 9.3%), and oral clefts (N = 19, 4.4%). Among the 40 cases with nervous system anomalies, 14 had neural tube defects.
Table 2 shows the distribution of selected maternal factors in the total population and among cases with LRD, all cases, after excluding genetic and chromosomal syndromes, and finally in isolated LRD using data from 1999 (N = 293 overall, 281 excluding TOPFA) due to better registration of associated anomalies after 1998. Prevalence of LRD in strata of maternal factors, with corresponding RRs are also shown. TOPFA cases were excluded except when analysing maternal age and parity, since TOPFA reports have lacked information on maternal factors other than age and parity until recent years. There were significantly more primiparous women among mothers of affected infants, and both being young (<20 years: adjusted RR (adjRR) 1.3 (95% CI 1.01–1.71) and 20–24 years: adjRR 1.2; 1.1–1.4) and old (> = 40 years: adjRR 1.6; 1.2–2.3) when giving birth was associated with increased risk of offspring total LRD. The association with high maternal age was, however, not statistically significant for non-syndromic or isolated LRD. The risk of offspring total LRD was more than three times higher in women with pre-gestational diabetes than in those without (adjRR 3.4; 2.0–5.7), and more than doubled for isolated LRD (adjRR 2.6; 1.1–6.3). There was no significant association between maternal epilepsy and offspring LRD, although only four mothers of isolated LRD cases had epilepsy. For infants born after 1998, daily smoking was at most weakly associated with offspring total LRD (adjRR 1.2; 0.9–1.6), and no relation was found with isolated LRD (adjRR 1.0; 0.7–1.5). Use of folate/multivitamin supplements before and/or during pregnancy was, on the other hand, associated with a 30% lower risk of offspring LRD compared to non-users, both for total (adjRR 0.7; 0.6–0.9) and isolated (adjRR 0.7; 0.6–0.98) LRD.
Table 2: Distribution of maternal factors in the total population and among limb reduction defects (LRD) cases, along with LRD prevalence by each factor. Table 2: Pregnancy terminations due to congenital anomalies are excluded except when analysing parity and maternal age.
Factor Total population Total LRD N (per 10 000) Total LRD Crude RR (95% CI) Total LRD Adj RRa (95% CI) Non-syndromic LimbRedDef Adj RRa,b (95% CI) Isolated LRDc Adj RRa (95% CI) Parity 0 1,147,173 612 (5.3) 1.0 (ref) 1.0 (ref) 1.0 (ref) 1.0 (ref) ≥ 1 1,597,939 594 (3.7) 0.7 (0.6–0.8) 0.7 (0.6–0.8) 0.7 (0.6–0.8) 0.7 (0.6–0.9) Maternal age (years) < 20 131,431 65 (4.9) 1.2 (0.9–1.6) 1.3 (1.0–1.71) 1.2 (0.9–1.6) 0.8 (0.3–2.1) 20–24 630,424 309 (4.9) 1.2 (1.0–1.4) 1.2 (1.1–1.4) 1.2 (1.1–1.4) 1.4 (1.0–1.9) 25–29 940,827 389 (4.1) 1.0 (ref) 1.0 (ref) 1.0 (ref) 1.0 (ref) 30–34 705,209 285 (4.0) 1.0 (0.8–1.1) 0.9 (0.8–1.1) 0.9 (0.8–1.1) 0.9 (0.7–1.3) 35–39 284,459 121 (4.3) 1.0 (0.8–1.3) 1.0 (0.8–1.2) 0.9 (0.7–1.1) 1.0 (0.7–1.4) 40+ 52,759 37 (7.0) 1.7 (1.2–2.4) 1.6 (1.2–2.3) 1.4 (0.9–2.0) 1.2 (0.6–2.3) Maternal pre-gestational diabetesd Yes 11,698 15 (12.8) 3.3 (2.0–5.5) 3.4 (2.0–5.7) 3.5 (2.1–5.8) 2.6 (1.1–6.3) No 2,729,202 1,062 (3.9) 1.0 (ref) 1.0 (ref) 1.0 (ref) 1.0 (ref) Maternal epilepsy Yes 16,393 8 (4.9) 1.2 (0.6–2.5) 1.2 (0.6–2.5) 1.3 (0.6–2.5) 2.1 (0.8–5.5) No 2,724,507 1,069 (3.9) 1.0 (ref) 1.0 (ref) 1.0 (ref) 1.0 (ref) Maternal daily smokinge 1.2 (0.9–1.6) 1.2 (0.8–1.6) 1.1 (0.7–1.5) Yes 134,351 56 (4.2) 1.3 (0.9–1.7) 1.2 (0.9–1.6)f 1.2 (0.9–1.6)f 1.0 (0.7–1.5)f No 740,154 246 (3.3) 1.0 (ref) 1.0 (ref) 1.0 (ref) 1.0 (ref) Use of folate/multivitamin supplementse 0.8 (0.6–1.02) 0.8 (0.6–1.01) 0.8 (0.6–1.07) Yes 661,066 195 (2.9) 0.7 (0.6–0.9) 0.7 (0.6–0.9)f 0.7 (0.6–0.9)f 0.7 (0.6–0.98)f No 287,249 122 (4.2) 1.0 (ref) 1.0 (ref) 1.0 (ref) 1.0 (ref)
- 7 Abbreviations: Limb reduction defects (LRD, LimbRedDef); Relative risk (RR); Confidence intervals (CI); Reference category (ref)
1
- 2
b Excluding cases with chromosomal and other syndromes; - 3
c Isolated LRD (N = 293 with and 281 without TOPFA), using data from 1999 due to better registration of associated anomalies after 1998. - 4
d Pre-gestational diabetes type 1, 2 and unspecified; - 5
e Data from 1999, missing smoking information 19%, missing folate information 12%; - 6
f Results when using multiple imputation to handle missing data in smoking and folate/multivitamins
Multiple congenital anomalies without known underlying causes may be a marker of teratogenic exposures [[
During 1999–2016, a total of 129 of 500 LRD cases were TOPFA (25.8%). Among these, associated anomalies were common, although 12 (9.3%) were registered with isolated LRD. On the other hand, a majority (77.5%) of the TOPFA cases had more than one associated anomaly, and in 31 cases (24%), major anomalies were registered in three or more additional subgroups. Other limb defects dominated also among TOPFA cases and were found in 40.3%, after which followed urinary defects (36.4%), cardiac defects (34.1%) and nervous system defects (33.3%), while chromosomal syndromes were found in 28 cases (21.7%). Of the total 129 TOPFA cases, 100 (77.5%) had an autopsy after termination, while five of the 12 TOPFA cases with isolated LRD (41.7%) had an autopsy.
After excluding TOPFA cases from 1999–2016, we analysed mortality among the remaining 1077 LRD cases for all years, 1970–2016 (Table 3, A) and, after also excluding associated major non-limb anomalies, for the remaining 281 cases born 1999–2016 (B). The last period was chosen since associated major anomalies were better registered from 1999. Overall, a total of 84% LRD cases were alive in 2016, based on updated data from the National registry, stillbirth was registered in 7.9% of cases, and among livebirths, 4.2% died during the first month (neonatal deaths) and 5.5% during the full first year (infant deaths). Thus, the risk of stillbirth was 7.4 times increased, neonatal mortality around 10 times increased and infant mortality 8.6 times increased compared to infants without LRD. However, after excluding associated major anomalies in other organs and looking only at infants born in 1999–2016, LRD did not seem to be associated with an increased mortality risk, although number of deaths were very few and confidence intervals were wide.
Table 3: Table 3: A: Mortality, low birth weight, preterm birth, and male sex among 1077 infants with limb reduction defects (LRD) relative infants without LRD during 1970–2016, terminations 1999–2016 excluded. B: Same outcomes among 281 infants with LRD relative infants without, 1999–2016, excluding terminations and LRD associated with major anomalies in other organs.
A Total LRD (1970–2016) Crude RR (95% CI) Adjusted RRa(95% CI) Outcomes No (reference) Yes Mortality Stillbirth (N, per 1000) 26,187 (9.6) 85 (78.9) 8.3 (6.7–10.1) 7.4 (6.0–9.3) Neonatal deathb(N, per1000) 10,909 (4.0) 42 (42.3) 10.5 (7.8–14.2) 10.1 (7.6–13.6) Infant death (N, per 1000)c 16,537 (6.1) 55 (55.4) 9.1 (7.0–11.8) 8.6 (6.7–11.1) Birth weight <2500 grams (N,%) 142,262 (5.2) 224 (20.8) 4.0 (3.6–4.5) 3.9 (3.4–4.3) Gestational age < 37 weeks (N, %) 179,396 (6.4) 201 (18.7) 2.9 (2.6–3.3) 2.7 (2.4–3.1) Sexd Male (N, %) 1,407,721 (51.4) 609 (57.1) 1.11 (1.05–1.17) B LRD without associated non-limb anomalies (1999–2016) Crude RR (95% CI) Adjusted RRa,e(95% CI) Outcomes No Yes Mortality Stillbirth (N, per 1000) 8,000 (7.4) 5 (17.8) 2.4 (1.0–5.7) 2.0 (0.8–5.4) Neonatal death (N, per 1000)b 2,262 (2.1) 0 NA NA Infant death (N, per 1000)c 3,193 (3.0) 1 (3.6) 1.2 (0.2–8.6) 1.1 (0.2–8.0) Birth weight <2500 grams (N, %) 57,344 (5.3) 36 (12.8) 2.4 (1.8–3.3) 2.3 (1.7–3.1) Gestational age < 37 weeks (N, %) 76,385 (7.1) 39 (13.9) 2.0 (1.5–2.6) 1.8 (1.4–2.5) Sex Male (N, %) 552,764 (51.4) 158 (56.4) 1.10 (0.99–1.22)
- 13 Abbreviations: Limb reduction defects (LRD); Relative risk (RR); Confidence intervals (CI); Not applicable (NA)
- 8
a Adjusted for time period (4-year categories), sex, maternal age (as categorized in Table 2) and maternal pre-gestational diabetes (yes/no); - 9
b First month of life; - 10
c First full year of life; - 11
d One stillbirth had unknown/unspecified sex; - 12
e Additional adjustment for maternal smoking (yes/no) and use of folate supplements (yes/no)
Among a total of 85 stillbirths with LRD, 59 (69.4%) were registered with associated anomalies; 45 of 66 (68%) in 1970–1998 and 14 of 19 (74%) in 1999–2016. Nervous system anomalies, other limb anomalies and abdominal wall defects were the most common associated anomaly groups in stillbirths in both periods. Among neonatal deaths, 39 of 42 (93%) were registered with associated anomalies (32 of 35 (91.4%) in 1970–1998 and all seven in 1999–2016). Here the most common associated anomalies in both periods were nervous system defects and cardiac defects.
The table also shows LBW, preterm delivery and male sex in the total population and in the two groups of LRD infants. LBW and preterm delivery was more common among affected infants, also among the cases without associated major anomalies from the last time period. As expected, there were more male cases, however, the male excess was slightly smaller among cases without associated major anomalies in the last time period.
This paper describes the results from a review and recoding of LRD cases in the MBRN, 1970–1998, and analyses done to evaluate the results of the recoding. The overall LRD prevalence, 1970–2016, was 4.4 per 10 000, with a slight increase in prevalence during the first decade, and relatively stable rates from 1982. There were more defects in upper than lower limbs, with defects in the hands and fingers being the most common. A large proportion of cases had associated anomalies, the most common being other limb defects. Associated anomalies were far better registered in the MBRN from 1999, and in this period, around one third of those with associated non-limb anomalies had acknowledged associations/syndromes. Among the non-syndromic cases, cardiac defects were the most common associated major anomalies, followed by anomalies in the nervous and digestive systems. From 1999, nearly 26% of limb reduction cases were terminated, however, more than 90% of these had associated major anomalies, with urinary defects, cardiac defects and nervous system defects being most frequent. Mortality was significantly higher among infants with LRD, but again, most of the increased mortality was related to associated major anomalies. Finally, we found that taking folate/multivitamin supplements before and/or during pregnancy was associated with lower risk of offspring LRD among children being born, while maternal daily smoking did not significantly increase the risk.
The overall prevalence of LRD in our study (4.4 per 10 000 in 1970–2016 and 4.6 per 10 000 in 1999–2016) was in agreement with a recent study by the EUROCAT association, describing European trends in congenital anomalies, 1980–2012 [[
In a Canadian study reviewing data from the Alberta Congenital Anomalies Surveillance System (ACASS), Bedard et al reported an average prevalence rate of congenital LRD at 5.6 per 10 000 births, 1980–2012 [[
In a registry-based study from Finland, where data from the Finnish Register of Congenital Malformations (FRCM) was used to describe CULA, the national incidence was 5.56 per 10 000 births, and 5.25 per 10 000 live births [[
Many previous studies have described associated anomalies in patients with LRD, but with a large range [[
We found that 7.2% of LRD cases 1999–2016 were associated with chromosomal syndromes, compared to 6.3% in the study by Stoll et al [[
LRDs are known to be associated with teratogenic exposures during pregnancy, such as maternal medication, where Thalidomide is the most well known. Other examples include antiepileptic/anticonvulsant drugs like phenytoin and valproic acid [[
We did not find a statistically significant association between maternal smoking and offspring LRD. This is in contrast to several previous studies [[
We found a 30% decreased risk of offspring total and isolated LRD associated with mothers taking folate/ multivitamin supplements before and/or during pregnancy (adjRR 0.7; 95% CI 0.6–0.9 and 0.6–0.98, respectively). This is close to what Shaw et al found in a small case-control study from 1995, where the odds ratio was 0.64 (0.41–1.0) [[
When comparing non-syndromic LRD cases who had associated anomalies ("LRD-multiples") with isolated LRD cases for their associations with pre-gestational diabetes, maternal daily smoking and use of folate/ multivitamin supplements, the point estimates could suggest a closer association of daily smoking and pre-gestational diabetes with LRD-multiples than with isolated LRD. However, since we had to exclude TOPFAs, the number of multiple cases was very small, and confidence intervals were wide and overlapping. We were therefore unable to draw conclusions. Daily smoking was not, however, associated with isolated LRD, in contrast to pre-gestational diabetes, where statistically significant associations were found with both LRD-multiples and isolated LRD. Hyperglycemia is a well-known teratogenic factor for a wide range of congenital anomalies [[
The present study was based on data from the MBRN alone. While information on some risk factors and life style habits are available in the registry, such as multivitamin/folate supplements and maternal smoking habits (both since 1999), others are not. Factors like maternal alcohol use or occupational exposures are not registered in the MBRN, and we were therefore unable to evaluate their possible associations with LRD.
We found increased risk of both stillbirth, neonatal death and infant death associated with LRD over the full time period. However, much of this increased mortality is likely related to the high proportion of associated anomalies. When excluding all cases with associated non-limb anomalies and looking only at the last time period where anomalies were better registered, there was no increased mortality risk associated with LRD. However, due to the very few deaths overall, this result must be interpreted with caution. The point estimate for stillbirth was compatible with a possible doubled risk associated with LRD although confidence intervals included 1.0, and we had inadequate power to disclose a potential true increase in risk of stillbirth.
Our aim was to review all LRD cases, 1970–1998, and recode from ICD-8 and internal codes to the more specific ICD-10, and to evaluate the results by comparing with published literature. The results for the recoded LRD group are mainly in agreement with the literature, and the MBRN now has ICD-10 codes for LRD cases back to 1970, a time when this version of the ICD was not yet in use. The MBRN is a nation-wide, population based registry with compulsory notification of all births in Norway since 1967, including late fetal losses, stillbirths and, since 1999, TOPFAs. Also since 1999, the registry has additionally received compulsory notification from NICUs for all infants transferred to such a unit after birth, and both these changes (TOPFA reports and NICU notifications) have led to a better ascertainment of congenital anomalies after 1998. Although LRD are rare congenital anomalies, we had enough data to look at specific limb defects, associated anomalies, and risk factors. For mortality we had enough data when looking at all LRD cases over the full study period, but when excluding associated non-limb anomalies and using data only after 1998, we lacked power to draw precise conclusions. Because notification to the registry is compulsory, selection bias is not a problem. The major limitation is that the information concerning LRD was often quite limited, especially before 1999 and especially concerning defects in the hands and feet, and we were therefore not able to classify the LRD cases according to established classification systems. The information on associated anomalies was also limited before 1999, making the years from 1999 the most valid for detailed analyses. For data from 1999, there was a relatively large proportion of missing information on maternal smoking habits and use of folate/multivitamin supplements, which we handled by multiple imputation after excluding TOPFAs. It is unfortunate that TOPFA cases did not have adequate information on maternal smoking, folate supplementation use or maternal chronic diseases.
We conclude that the MBRN now has information on LRD coded by ICD-10 from 1970, but that the information is not detailed enough to use established limb classification systems. Since aetiology may vary between the specific groups of LRD, we recommend that the registry collects radiographic descriptions or more detailed information from hospital records for these rare congenital anomalies. With a total prevalence at birth of less than 5 per 10 000 and a likely number of annual cases around 25–30 per year, we hope this is achievable. A prospective medical quality and research registry on all CULA cases was recently established in Division of Orthopaedic Surgery, Oslo University Hospital, which includes more specific and clinically relevant details on cases. This will be a good supplement to the MBRN, providing exciting possibilities for future data linkage.
S1 Table. Distribution of specific reduction defects in the two time periods (1970–1998: N = 706 cases, and 1999–2016: N = 500 cases), and for the whole study period (1970–2016, N = 1206 case). The Medical Birth Registry of Norway, 1970–2016. (DOCX)
DIAGRAM: Fig 1: Time trends in overall prevalence (per 10 000) of limb reduction defects, 1970–2016, using original coding (ICD-8 and internal codes during 1970–1998, ICD-10 from 1999) and new coding (ICD-10 for all years). Year 1999 marks changes in the MBRN that have increased ascertainment of congenital anomalies.
DIAGRAM: Fig 2: Prevalence (per 10 000) of limb reduction defects in upper, lower and unspecified limb, 1970–2016.
DIAGRAM: Fig 3: Distribution of associated major congenital anomalies (%) among limb reduction defect cases in 1970–1998 and 1999–2016.
We thank Rannveig Aardal and Torill Holmar at the Norwegian Institute of Public Health for help finding the needed birth notification forms, 1970 to 1998, from storage.
By Kari Klungsøyr, Writing – review & editing; Tone Irene Nordtveit, Writing – review & editing; Trine Sand Kaastad, Writing – review & editing; Sigrun Solberg, Writing – review & editing; Ida Neergård Sletten, Writing – review & editing and Anne-Karin Vik, Writing – review & editing