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RESEARCH: Jens Langhoff-Roos, Ulrik Kesmodel, Bo Jacobsson, Steen Rasmussen, and Ida Vogel Spontaneous preterm delivery in primiparous women at low risk in Denmark: population based study BMJ 2006; 332: 937-939 [Abstract] [Full text]

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Preterm birth or preterm delivery? Suggestions for new terms

Ida Vogel, Ulrik Kesmodel, Steen Rasmussen, Jens Langhoff-Roos and Bo Jacobsson   (24 February 2006)

Are Danish mothers consuming more licorice?

Timo E Strandberg   (21 April 2006)

Preterm deliveries in Scotland

James W Chalmers, Etta Shanks, Anne Stott, Catherine Paton   (22 April 2006)

Radiation Risk Ignored in Preterm Delivery Study

Lynn Howard Ehrle   (22 April 2006)

Study on preterm births does not consider effect of induced abortion

Trevor G Stammers   (23 April 2006)

Could Lletz be responsibe

David JR Hutchon   (23 April 2006)

Could epidemic chlamydia contribute to this rise in preterm births?

Woody Caan   (24 April 2006)

What about terminations?

Peter JM Davis   (28 April 2006)

Maternal age and spontaneous premature delivery

Erika Sievers MD PhD MPH   (3 May 2006)

Preterm birth or preterm delivery? Suggestions for new terms 24 February 2006
Ida Vogel, MD, PhD NANEA at the Institute of Public Health, University of Aarhus, 8000 Aarhus, Denmark, Ulrik Kesmodel, Steen Rasmussen, Jens Langhoff-Roos and Bo Jacobsson Send response to journal: Re: Preterm birth or preterm delivery? Suggestions for new terms	The term preterm birth is used differently in the literature; some use preterm birth to refer to the number of infants born before 37 completed weeks (1;2) while others use the term to specify the number of pregnancies ending before 37 completed weeks (3). Still others have restricted their analyses to singleton pregnancies in order to avoid this difference (4). The use of the alternative term preterm delivery varies in a similar fashion. We noticed this difference in the current study looking at infants born preterm and pregnancies ending preterm in Danish national data from 1995-2004. Thus, we found that the national proportion of preterm infants rose from 5.8% (4019/69013) in 1995 to 7.2% (4650/64223) in 2004; an increase of 24%. However, when mothers or pregnancies were counted, the proportions were 5.2% (3509/67840) in 1995 and 6.3% (3975/62814) in 2004, an increase of 22%. This discrepancy can easily be explained, as the proportion of twin gestations rose from 1.7% to 2.3% of all gestations during this ten-year period. When analyzing published we often asked ourselves: “Does a twin pregnancy that ends at 32 weeks count as one or two preterm births?” From the obstetrician’s point of view it is most likely one preterm birth but two from a paediatric standpoint. The quality of the data collected for many national registers and studies make it possible to initiate this distinction. In order to compare such data over time, as well as between populations, it is important that there be agreement on the definitions of these terms, especially at a time in which the proportion of twin pregnancies is increasing. The importance of identical international definitions in perinatal health is a precondition for evaluation of differences in outcomes between populations has already been recognized in the PERISTAT project (5). We therefore propose two different, new and distinguishable definitions: a preterm ending pregnancy (PTP) ends before 37 completed weeks, and a preterm born infant (PTI) is born before 37 completed weeks. Thus, a twin pregnancy delivered at 32 weeks will be counted as one PTP (preterm ending pregnancy), but two PTI (preterm born infants). Reference List 1. Martin JA, Hamilton BE, Sutton PD, Ventura SJ, Menacker F, Munson ML. Births: final data for 2002. Natl.Vital Stat.Rep. 2003;52:1-113. 2. Kogan MD, Alexander GR, Kotelchuck M, MacDorman MF, Buekens P, Martin JA et al. Trends in twin birth outcomes and prenatal care utilization in the United States, 1981-1997. JAMA 2000;284:335-41. 3. Morken NH, Kallen K, Hagberg H, Jacobsson B. Preterm birth in Sweden 1973-2001: Rate, subgroups, and effect of changing patterns in multiple births, maternal age, and smoking. Acta Obstet.Gynecol.Scand. 2005;84:558-65. 4. Ananth CV, Misra DP, Demissie K, Smulian JC. Rates of preterm delivery among Black women and White women in the United States over two decades: an age-period-cohort analysis. Am.J.Epidemiol. 2001;154:657-65. 5. Buitendijk S, Zeitlin J, Cuttini M, Langhoff-Roos J, Bottu J. Indicators of fetal and infant health outcomes. Eur.J.Obstet.Gynecol.Reprod.Biol. 2003;111 Suppl 1:S66-S77. Competing interests: None declared
Are Danish mothers consuming more licorice? 21 April 2006
Timo E Strandberg, Professor Department of Public Health Science and General Practice, University of Oulu, PO Box 5000, FIN-90014 Send response to journal: Re: Are Danish mothers consuming more licorice?	In our GLAKU project of 1049 mothers and their babies in Finland (1) we found a new risk factor of preterm birth. Infants of mothers, who were frequent consumers of licorice confectionery, were significantly more likely to be born earlier. The odds ratio for being born before 38 weeks’ gestation time was 2.5. The mechanism may be due to glycyrrhizin in licorice, and its interference with prostaglandin metabolism. The consumption of licorice is common among Finnish women, but I do not know the habits of Danish mothers in this respect. Has licorice consumption by any chance increased in Denmark during the last few years? 1. Strandberg TE, Jarvenpaa AL, Vanhanen H, McKeigue PM. Birth outcome in relation to licorice consumption during pregnancy. Am J Epidemiol 2001;153:1085-8 Competing interests: None declared
Preterm deliveries in Scotland 22 April 2006
James W Chalmers, Consultant in Public Health Medicine Information Services Division, NHS National Services Scotland, Gyle Square, Edinburgh. EH14 5BE, Etta Shanks, Anne Stott, Catherine Paton Send response to journal: Re: Preterm deliveries in Scotland	Langhoff-Roos and colleagues have used routine data from Denmark to demonstrate a recent rise in preterm deliveries, particularly amongst low risk primiparous women.  Scotland is also able to furnish comparable routine data, derived from the maternity dataset of the Scottish Morbidity Record (SMR02).  From this dataset we have attempted to emulate Langhoff-Roos and colleagues’ approach and present data on preterm (before 37 weeks gestation) deliveries for all women, and for “low risk” women aged 20-40 who were not delivered by caesarean section or induction (see Table).  We were unable to limit the analysis to women of European origin, but the proportion of Scottish women who are of non-European origin is approximately 2%. Table: Preterm deliveries in Scotland. Proportion of all deliveries, and proportions of spontaneous singleton live births excluding elective caesarean sections and inductions, for primiparous and multiparous women.               Year   % All   % Low risk women             Primiparous   Multiparous 1980   5.8   6.6   5.2 1981   5.4   6.5   5.1 1982   5.6   6.5   5.1 1983   6.0   6.6   5.4 1984   6.3   6.7   5.5 1985   6.0   6.7   4.8 1986   6.1   6.4   5.1 1987   6.2   6.4   5.0 1988   6.4   6.5   5.3 1989   6.3   6.4   4.8 1990   6.5   6.7   5.5 1991   6.4   6.6   5.1 1992   6.8   6.9   5.2 1993   6.3   6.7   4.9 1994   6.7   7.0   5.3 1995   6.8   7.3   5.3 1996   7.1   7.0   5.7 1997   7.0   6.7   5.9 1998   7.1   7.7   6.0 1999   7.3   7.7   6.5 2000   7.4   8.3   6.3 2001   7.3   8.0   6.2 2002   7.5   8.1   6.4 2003   7.8   8.4   6.9 2004p   7.6   8.0   6.5 p - provisional           Source: SMR02           For the same time period (1995 – 2004) used by Langhoff-Roos and colleagues, the proportion of preterm deliveries overall has risen by 11%.  The proportion of preterm deliveries in the “low risk” category has risen by 9% for primiparous women but by 24% for multiparous women, which is in contrast to the findings in Denmark.  However, the level of preterm births in Scotland is consistently higher in all the above groups compared to those of Denmark.  The trend in the “low risk” women appears to have started to rise from the late nineteen eighties.  It is likely that there are some differences between the datasets of these two countries in terms of completeness and accuracy, and there have been some changes in the way that the Scottish data have been collected and recorded over this time period, but these are unlikely to explain most of the disparities.  Langhoff-Roos and colleagues’ idea of using a standard population of low risk primiparous women to encourage comparative studies is very welcome.   Email address for correspondence: jim.chalmers@isd.csa.scot.nhs.uk   Competing interests: None declared
Radiation Risk Ignored in Preterm Delivery Study 22 April 2006
Lynn Howard Ehrle, Senior Biomedical Policy Analyst 8888 Mayflower Dr,, Plymouth, Michigan, 48170 Send response to journal: Re: Radiation Risk Ignored in Preterm Delivery Study	The Danish study analysing trends in preterm delivery (22 April)failed to identify radiation exposure as a key risk factor. The 2003 European Committee on Radiation Risk Study, Health Effects of Ionising Radiation Exposure at Low Doses for Radiation Protection Purposes, edited by Scientific Secretary Chris Busby, cites an upward trend in infant mortality and stillbirths after the Mayak weapons facility releases and the Chernobyl accident. Until and unless researchers, clinicians, and government policy makers pay greater attention to the necessity for reduction in low-dose exposures from nuclear reactors and medical X ray, in utero and genetic effects will cause the trend line to continue its upward climb. Competing interests: None declared
Study on preterm births does not consider effect of induced abortion 23 April 2006
Trevor G Stammers, Senior Tutor in General Practice St George's, University of London Send response to journal: Re: Study on preterm births does not consider effect of induced abortion	It is noteworthy that the BMJ publishes both original research(1) and an editorial(2) on why preterm births are rising, without any mention of abortion in either paper (though Shennan and Bewley do al least mention optimising “surgical treatment of the cervix to avoid cervical damage”). A recent review of long-term consequences of abortion(3) reported that 12 out of 24 studies found an association between induced abortion and subsequent preterm births and 7 of these 12 studies also found a “dose -response” effect. Since this review, the EPIPAGE study(4) in France concluded that “Previous induced abortion was associated with an increased risk of very preterm delivery. The strength of the association increased with decreasing gestational age”. Surely with abortions in the UK now exceeding 200 000 a year, the evidence indicating a link with preterm births deserved at least a mention or else evidence that there is no such association should have been presented to reassure the thousands of women undergoing terminations of pregnancy each week? 1. Langhooff-Roos J, Kesmodel U, Jacobsson B et al Spontaneous preterm deliver in primiparous women at low risk in Denmark: population based study. BMJ 2006 332 937-9 2. Sheenan Ah, Bewley S Why should preterm births be rising? BMJ 2006 332 924-5 3. Thorp JM Hartmann KE Shadigian ES Long term physical and psychological health consequences of induced abortion: review of the evidence. Obs and Gynae Survey 2002 58 67-79 4. Moreau C, Kaminski M, Ancel PY, et al Previous induced abortions and the risk of very preterm delivery: results of the EPIPAGE study. BJOG 2005 112 430-37 Competing interests: None declared
Could Lletz be responsibe 23 April 2006
David JR Hutchon, Consultant Obstetrician and Gynaecologist Darlington Nenorial Hospital, DL3 8QZ Send response to journal: Re: Could Lletz be responsibe	It mihgt be worth looking at any regional differences in the preterm delivery rates in Scotland reported by James W Chalmers, Consultant in Public Health Medicine Information Services Division, NHS National Services Scotland, Gyle Square, Edinburgh. EH14 5BE, Etta Shanks, Anne Stott, Catherine Paton as I understand that Deeside and Ninewells Hospital, Dundee have not adopted the routine use of Lletz for the treatment of CIN but have continued to use cold coaguation. Cold coagulation may cause less damage to the cervix. Although Lletz was not thought to cause any damage, recent evidence does show this treatment is associated with an increased risk of preterm labour. The Dundee area is probably one of the few areas in the world where Lletz has not been adopted as routine. The effectiveness of the treatment however appears to be just as good. Perhaps Chalmers et al can look at their data on a regional basis. Competing interests: None declared
Could epidemic chlamydia contribute to this rise in preterm births? 24 April 2006
Woody Caan, Professor of public health Anglia Ruskin University, Chelmsford CM1 1SQ, UK. Send response to journal: Re: Could epidemic chlamydia contribute to this rise in preterm births?	The rise in preterm births described in Denmark [1] would give cause for concern, in terms of long-term health consequences, in any country. One risk factor that is not described in this study is infection with Chlamydia [2], which is rising rapidly among young women in urban areas of the UK. Given that most affected patients are unaware of their infection, and that specialist screening and treatment facilities are not easily accessible for most populations, could this be the 'invisible' factor driving higher rates of premature babies, among 'low risk' mothers? 1 Langhoff-Roos J, Kesmodel U, Jacobsson B, Rasmussen S, Vogel I. Spontaneous preterm delivery in primiparous women at low risk in Denmark: population based study BMJ 2006; 332: 937-939. 2 Caan W. Implications for the economic evaluation of other screening programmes e.g. for chlamydia. http://bmj.bmjjournals.com/cgi/eletters/329/7462/371#69924 (5 August 2004). Competing interests: Supervising a community research project on chlamydia.
What about terminations? 28 April 2006
Peter JM Davis, GP Whitnash Medical Centre, 110 Coppice Rd, Whitnash, Leamington Spa, Warwickshire CV31 2LT Send response to journal: Re: What about terminations?	“… degree of surgical trauma is related to the risk of preterm birth”, state Shennan & Bewley in their leading article related to this paper. The commonest surgical trauma to the cervix must be termination of pregnancy. There is a doubling of the risk of preterm labour after termination (The care of women requesting induced abortion. RCOG 2004; September: 34). Why was this fundamental factor not mentioned by Langhoff-Roos et al? Its absence invalidates their whole paper. Competing interests: None declared
Maternal age and spontaneous premature delivery 3 May 2006
Erika Sievers MD PhD MPH, Pediatrician Institute of Public Health, North Rhine Westphalia; Von-Stauffenberg-Str. 36 D-48151 Germany Send response to journal: Re: Maternal age and spontaneous premature delivery	The authors define a standard population of "women at low risk” consisting of white European primiparous women aged 20-40 with a singleton spontaneous pregnancy. The age-specific fertility rates across different cohorts of the same age have been compared in selected OECD countries ( http://www.oecd.org/dataoecd/7/33/35304751.pdf ). On the one side, in Denmark and other nations the age-specific fertility rates of women aged 20-24 have fallen strongly over time. On the other side, they increased steadily for women aged 30 to 34 and 35 to 39. A much larger proportion of childbearing takes place today when women are in their 30s (1). This implies that the average of primiparous women has shifted to older ages. It is suggested that international comparisons of preterm delivery rates should take into account the respective development of age-specific fertility rates. This would imply a maternal age-stratified analysis of pregnancy outcome comparing the age-specific subgroups in the intervals where major changes of fertility rates have been observed. (1) d’Addio AC, d’Ercole MM: Trends and determinants of Fertility Rates in OECD Countries: The Role of Policies. OECD SOCIAL, EMPLOYMENT AND MIGRATION WORKING PAPERS No. 27, 02-Nov-2005; DELSA/ELSA/WD/SEM(2005)6 Competing interests: None declared