Intergenerational recurrence of breech deliveryBMJ 2008; 336 doi: https://doi.org/10.1136/bmj.39527.608542.80 (Published 17 April 2008) Cite this as: BMJ 2008;336:843
- Janet R Hardy, assistant professor of medicine, obstetrics/gynecology, and pediatrics
- 1Department of Medicine; Division of Preventive and Behavorial Medicine, University of Massachusetts Medical School, Worcester, MA 01655, USA
Much attention has been focused on the consequences of breech presentation and on strategies to minimise risk for both the fetus and the mother. Studies, including the landmark term breech trial, have had a positive effect on clinical practice and set a standard in developed countries of caesarean delivery for persisting breech presentation.1 2 3 Less attention, however, has been focused on why some fetuses deliver in breech position. In the accompanying paper, Nordtveit and colleagues investigate whether the risk of breech delivery can be passed on through generations via both men and women.4
The prevalence of breech presentation decreases through gestation as fetuses mature, and most fetuses move into cephalic position before delivery. The prevalence of breech presentation is 25% at 28 weeks’ gestation and 3-4% at term.5 Risk factors include maternal characteristics (primiparity, contracted pelvis, high maternal age, and uterine abnormality); characteristics of the pregnancy (multifetal gestation and placental implantation site); and fetal factors (preterm birth, growth retardation, neuromuscular dysfunction, and malformations).6 7 8 9 10
The high recurrence of breech presentation between siblings may largely be attributable to the maternal uterine environment.11 However, recurrence between generations suggests that one or more genetic factors may be passed from the parent to the developing fetus. Nordtveit and colleagues investigated this possibility by using the medical birth registry of Norway.4 This registry is a population based compulsory registry of all live births and still births of 16 weeks’ or more gestation.4 It contains the records of more than 2 million births in Norway since 1967 and is a respected resource for medical and public health research.
Using registry data, the authors linked mothers’ and fathers’ birth records (1967-86) to the records of their offspring (1987-2004). First born singleton offspring with a birth weight of 500 g or more and their parents were included in the study. To investigate paternal effects, paternal half sibling births were also examined. The authors evaluated multiple factors in the parental histories in relation to breech delivery in the offspring.
The authors’ main conclusion was that an increased risk of breech delivery in first born offspring was associated with both a maternal and a paternal history of breech delivery at term. The paternal effect was as strong as the maternal effect (odds ratio maternal 2.2, 95% confidence interval 1.9 to 2.5; paternal 2.2, 1.8 to 2.7).4 These findings are novel and intriguing, but are they robust?
Overall, the authors’ results seem plausible. However, further discussion of missing data, possibly inaccurate or inconsistently recorded data, and of potential misclassification would have been helpful. For example, an improved data collection tool with a checkbox for breech delivery was introduced in 1999, and breech delivery may have been misclassified in both parents and offspring before this date. It would have been informative to discuss how this could have influenced the results, especially as the prevalence of breech presentation increased over the study period.
Interestingly, some of their results on maternal and paternal birth order might suggest less of a genetic trait for breech presentation than an environmental factor or interaction. A breech trait is unlikely to be preferentially passed to offspring from first born rather than second born parents. Future research looking at the offspring’s uterine environment and specific characteristics (for example, specific major malformations) in the context of parental birth factors may provide some insight into the authors’ reported maternal and paternal effects.
Members of Nordtveit’s team have published other articles on breech presentation and have used the Norwegian registry for generating and testing hypotheses.4 10 12 These and other observational studies that use large linked population databases, such as the medical birth registry of Norway, are of value and are especially useful for research questions that need large study samples. Multiple biological mechanisms probably contribute to the risk of breech presentation—some genetic (maternal or paternal, or both), some related to the uterine environment, and some a combination of both. Nordtveit and colleagues’ findings are novel, but strength of evidence will come from consistent conclusions across multiple epidemiological and laboratory investigations.
So what should clinicians do in the meantime? It is premature to advise mothers of a higher risk of a breech delivery if their parents had a breech delivery. However, clinicians should continue to gather information during early prenatal care on maternal and paternal birth presentation and other potential risk factors for breech delivery. This combined information may serve to alert the clinician and patient to the possibility of breech presentation and that they should discuss planned external cephalic version or caesarean section delivery (or both).
Competing interests: None declared.
Provenance and peer review: Commissioned; not externally peer reviewed.