Date Published: September 22, 2009
Publisher: Public Library of Science
Author(s): Jane E. Norman, Carole Morris, James Chalmers, Peter Brocklehurst
Abstract: Jane Norman and colleagues analyzed linked perinatal surveillance data in Scotland and find that between 1980 and 2004 increases in spontaneous and medically induced preterm births contributed equally to the rising rate of preterm births.
Partial Text: Preterm birth is the pre-eminent problem facing perinatologists in developed countries and has been defined as a major public health problem whose magnitude is increasing . Although the secular trend is of an improvement in gestation specific outcomes (at least in terms of mortality) ,, absolute rates of preterm birth are increasing in both the US  and in European countries such as the UK , and Denmark . Thus prematurity arising from preterm birth remains the biggest single cause of perinatal mortality and morbidity in most developed countries . Governments and health care providers are increasingly concerned about this issue, and there have been calls for action from many bodies ,.
We explored the SMR02/SMR11/SBR/SSBID/GROS Birth Database (“The Linked Maternity and Neonatal Database”). This database contains linked maternity, neonatal, and stillbirth/infant death records, with records pertaining to mother and baby held together. The SMR02 (Scottish Morbidity Records 2) return is completed at the time of discharge of any patient from a Scottish maternity hospital and the level of completeness over the period studied is estimated to be in excess of 98%. There is also a facility for the data to be returned in the case of home births but this is thought to be less complete. However, home births in Scotland during this period comprised less than 1% of all births, so this is unlikely to be a source of significant error. SMR11 (now replaced by Scottish Birth Record, or SBR) are routine neonatal returns. SSBID is a record relating to Stillbirths and Infant Deaths, based on stillbirths and infant deaths that are registered with the General Register Office for Scotland (GROS). For each SSBID event, further information is sought from the relevant hospital. Because the data are based on registered events, it is unlikely that any cases are missed.
At the outset of this study, we hypothesised that, in contrast to reports from the US and Latin America (which highlight an increase in elective delivery), increased rates of idiopathic spontaneous labour (with or without pPROM) would be a major contributor to the increase in preterm birth rates observed in Scotland. Our hypotheses were partially correct—although the percentage increase in preterm birth rates was greatest in the elective/induced category (a 41% increase over the study period), rates of preterm birth were also rising in the spontaneous preterm birth category (a 10% rise over the study period). These changes persist when adjusted for maternal age: a progressive rise in the proportion of preterm births (in both the elective and spontaneous category) would have occurred even if there had been no change in maternal age over the study period. Although the percentage rise in elective/induced preterm births is greater than that in spontaneous preterm births (with and without pPROM), the absolute increase in the rate of preterm births is similar in each group (4.24 compared with 4.71 per 1,000 singleton births, respectively [Table 1]). Thus, in our population, increases in spontaneous and elective/induced preterm births are making equal contributions to the rise in the rate of preterm births. Our results showing an increase in both elective/induced and spontaneous preterm birth rates contrast with those of Ananth and colleagues, who showed a 50% increase in the rate of medically indicated preterm birth in the US from 1989 to 2001, but a 5%–25% decline in spontaneous preterm birth (with and without pPROM) , and those of Barros and Velez Mdel, who showed a 80% increase in medically indicated preterm birth in Latin America between 1985 and 2000 due to elective induction/delivery but again a decline in spontaneous preterm birth and that associated with pPROM . The discrepancy with the Barros paper may in part relate to the fact that we included women with gestational or pre-existing diabetes in contrast to Barros and Velez Mdel, who excluded them, especially since the contribution of both of these complications to preterm birth (in our population) increased significantly over the study period. Our results are in keeping with those of Langoff Roos et al.  and Tracy et al. , who showed a rise in spontaneous preterm deliveries over a 10-y period in both populations as a whole, and in specially constructed “standard” populations of low risk women.