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Sir,

We read with interest the paper by Rasmussen et al) (Vol 104, November 1997) addressing the effect on the likelihood of further pregnancy after a placental abruption and the rate of recurrence. The authors intended to investigate the reproductive career of the women who had previously suffered from a placental abruption using routinely notified data from Medical Birth Registry of Norway. Despite large number of cases, the conclusions drawn from the analysis of the data based solely on the Medical Birth Registry face several problems because of its inherent difficulties of case ascertainment, which also has been emphasised in a previous Swedish study2.

In this Norwegian study there is no particular mention of the diagnostic criteria of placental abruption. Sometimes it is difficult to differentiate between minor placental abruption and unexplained antepartum haemorrhage and that could prevent subsequent investigators reproducing the results. Developments in ultrasound over this long study period could have influenced the diagnosis and management of antepartum haemorrhage, although the sensitivity of sonography in the diagnosis of placental abruption is known to be poor3.

Early pregnancy loss, an important determinant of reproductive outcome, has not been included in this study. As these routinely collected data included only pregnancies t 16 weeks' gestation, it is probably impossible to address this issue.

It is interesting to find that “more than 10% of the women with a history of placental abruption without perinatal loss do not achieve the family size they desire” and this is “constant throughout the study period”. It is important to consider the trend of small family norm in developed countries over the last two decades and that it is impossible to dismantle the relative contribution of social and medical factors.

Caesarean sections have been shown to be an independent risk factor for subsequent abruption and placenta praevia4. Has the rising rate of Caesarean sections from 2% in 1967–1972 to 12% in 1985–1989 observed in this study any influence on the recurrence rate?

In conclusion the authors must be congratulated for their considerable effort in performing such a large study. However, a cohort study with appropriate predefined diagnostic criteria for placental abruption and inclusion of all important pregnancy outcomes may resolve the questions raised in this correspondence.

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