Validation of the danish birth registration

Abstract

We assessed validity and reliability of data on four serious pregnancy complications and gestational age in two national registers, the Medical Birth Register (MBR) and the National Register of Hospital Discharges (NRHD). From a cohort of all women in Denmark who gave birth to their first and second singleton infant in 1982-1987, a review was made of a selected sample of 1662 medical records. Regarding registration of pregnancy complications, there was good agreement (kappa above 0.6) between medical records and the registers, and between the registers. However, there was a tendency toward understatement evidenced by low sensitivity of three of four pregnancy complications. The level of agreement (43%) for length of gestation was disappointing. The number of systematic and nonsystematic errors indicate that there was about 52% more singleton preterm deliveries in Denmark in 1982 than previously reported (6.9% instead of 4.5%). It is concluded that the validity of the Danish birth registers should be improved by explicit definitions, increased use of raw data, and data collection by motivated professionals at birth.

Birth outcome in women with breast cancer

“…However, breast cancer treatment with surgery alone was correctly registered for 95.4% (Jensen et al, 2002). Coding mistakes are infrequent in the Birth Registry, but data have some misclassifications of gestational age (Kristensen et al, 1996). Our data did not suggest any differential misclassification of preterm birth between women with breast cancer and comparison mothers.…”

“…We excluded all cases of 'Carcinoma in situ' and six cases of sarcoma involving the breast. Women with breast cancer were linked to the Danish Medical Birth Registry with data on all births in Denmark since January 1, 1973 (Kristensen et al, 1996) obtained from birth notifications, filled in by midwives (in Denmark all births, including home births, are attended by midwives). The main variables are the civil registration number of the mother and child, date and place of birth, gestational age, birth weight, and parity.…”

Low Birth Weight in Children Born to Mothers with Hyperthyroidism and High Birth Weight in Hypothyroidism, whereas Preterm Birth Is Common in Both Conditions: A Danish National Hospital Register Study

“…Misclassification of exposure and/or outcome exists in our study population including misclassification of maternal thyroid disease onset in relation to pregnancy period [42] ; however, we believe any misclassification is nondifferential, which would often create bias towards the null.…”

First-Trimester Exposure to Methylphenidate

“…12,13 More than 99% of all births in Denmark have been recorded in the Medical Birth Registry, and completeness of the National Prescription Registry has been estimated to be 98%. 13,28 The diagnoses of malformations have been found to have a predictive value of 88% for congenital malformations, with a completeness of 90%, and misclassification was probably random. 29 It is, however, conceivable that some newborns exposed to methylphenidate in utero will be more diligently 30 If this is the case, it will only strengthen our conclusion that methylphenidate is safe in pregnancy.…”