Papers

Historical cohort study of in utero exposure to uterotonic drugs and cognitive function in young adult life

BMJ 1999; 318 doi: https://doi.org/10.1136/bmj.318.7181.433 (Published 13 February 1999) Cite this as: BMJ 1999;318:433
  1. Henrik Toft Sørensen, associate professor (hts{at}soci.au.dk)a,
  2. Kenneth J Rothman, professorc,
  3. Matthew W Gillman, associate professord,
  4. Flemming Hald Steffensen, research associate professorb,
  5. Peer Fischer, consultante,
  6. Svend Sabroe, associate professorb
  1. aDepartment of Internal Medicine V, Aarhus University Hospital, 8000 Aarhus C, Denmark
  2. bDanish Epidemiology Science Centre, Department of Epidemiology and Social Medicine, University of Aarhus, 8000 Aarhus C
  3. cDepartment of Epidemiology and Preventive Medicine, Boston University School of Medicine, Boston, MA 02118, USA
  4. dDepartment of Ambulatory Care and Prevention, Harvard Medical School and Harvard Pilgrim Health Care, Boston, MA 02215
  5. eConscription Administration, County of North Jutland, 9000 Aalborg, Denmark
  1. Correspondence to: Dr Sørensen
  • Accepted 14 August 1998

Oxytocin has potent uterotonic properties which can induce tetany, rupture, and water intoxication. Inappropriately high doses can affect the fetus by inducing abnormal heart rhythms, circulatory collapse, and preterm delivery accompanied by an increased risk of respiratory distress and damage to the central nervous system.1 Several studies have reported an association between oxytocic drugs and neonatal hyperbilirubinaemia,2 which might influence long term cognitive function.3 Little is known, however, of the long term consequences of exposure to uterotonic drugs. We investigated whether in utero exposure to uterotonic drugs affects cognitive performance in draft age men.

Subjects, methods, and results

Nearly all Danish men have to register with the draft board at around the age of 18years, at which time they undergo physical and mental examinations. We studied all men who were born in Denmark after 1January 1973and who were drafted while residing in North Jutland and Viborg counties from 1August 1993to 31July 1994.

All draftees took a 45minute intelligence test, the Boerge Prien test, developed in 1957for the Danish draft board.4 The test includes four time limited subtests covering four categories: letter matrices, verbal analogies, number series, and geometric figures. The test shows high correlations with the Weschler adult intelligence scale verbal intelligence quotient (0.78), the performance intelligence quotient (0.71), and the full scale intelligence quotient (0.82). In the validation study the mean full scale intelligence quotient was 106,equivalent to a mean Boerge Prien test score of 44.2.4

We linked data from the draft examination with the Danish Medical Birth Registry by means of a 10digit unique personal identification number. The registry contains information relating to all births in Denmark since 1973.Oxytocin was the most commonly used uterotonic drug in that period. We examined the mean Boerge Prien test score according to in utero exposure to uterotonic drugs, taking account of possible confounding variables (table).

Descriptive data on 4300 Danish draftees* according to exposure to uterotonic drugs during their delivery. Figures are numbers (percentages) of subjects unless stated otherwise

View this table:

We identified 4805conscripts during the study period. We had complete draft medical data on 4300; of the remainder, 495were exempt from the examination mainly because of asthma, osteochondrosis, and epilepsy, and 10had incomplete data in the birth registry. Of the 4300men, 22.8% had been exposed to uterotonic drugs; among those who were exempt from the examination 23.5% had been exposed to uterotonic drugs.

The mean Boerge Prien score was similar for those exposed and not exposed to uterotonic drugs (43.1v 42.9). We also stratified the subjects by mode of delivery; in subjects born by vaginal delivery the mean Boerge Prien score was 43.0among those exposed to uterotonic drugs compared with 43.1among those not exposed. From a multiple linear regression with all above mentioned confounders included we estimated the difference in Boerge Prien score to be −0.58 (95% confidence interval −1.25 to 0.08) between those exposed and not exposed to uterotonic drugs.

Comment

Friedman et al examined 156children 23to 62months after births associated with spontaneous labour, labour induced with oxytocin, or labour induced with dinoprostone. The prevalence of neurological or developmental abnormalities not attributable to events after delivery was the same overall in induced and spontaneous labours, but those abnormalities occurring after induction of labour all followed use of oxytocin.5 Our data indicate that exposure to uterotonic drugs does not substantially affect cognitive function 20years later. A small difference due to non-differential misclassification, however, cannot be ruled out. A strength of our study is the large size, the population based design, and complete ascertainment. It is unlikely that selection bias and confounding explain the lack of association.

Acknowledgments

Contributors: HTS, KJR, and MWG in collaboration with SS initiated the establishment and design of the cohort. HTS initiated this study and discussed the hypothesis with KJR. HTS and FHS analysed the data. PF collected the outcome data. SS linked the data to the birth registry. All authors participated in the interpretation of the findings. HTS, KJR and FHS wrote the first draft of the paper. All participated in editing the paper. HTS is guarantor of the paper.

Funding: Helsefonden (grant No 11/064-94), the EU Biomed II programme (contract No BMH4-CT97-2430), Aarhus University Research Foundation (F-1996-SUN-1-77), and Danish Medical Research Council (grant No 9700677). The activities of the Danish Epidemiology Science Centre are financed by a grant from the Danish National Research Foundation.

Conflict of interest: None declared.

References

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