Effects of gestational age at birth on health outcomes at 3 and 5 years of age: population based cohort study

BMJ 2012; 344 doi: http://dx.doi.org/10.1136/bmj.e896 (Published 1 March 2012)
Cite this as: BMJ 2012;344:e896

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The authors (1) have not discussed the most important perinatal health outcome that varies with gestation beyond term - death of the baby.

Delivery at 38 weeks gestation is associated with the lowest perinatal mortality (2,3). The risk increases thereafter in all pregnancies.

The survival benefit of earlier delivery more than compensates for this study's additional morbidity (confounded as it must be by maternal disease & placental pathology causing early delivery).

(1) Boyle EM et al Effects of gestational age at birth on health outcomes at 3 and 5 years of age: population based cohort study BMJ 2012; 344 doi: 10.1136/bmj.e896

(2) Smith GC Life-table analysis of the risk of perinatal death at term and post term in singleton pregnancies. Am J Obstet Gynecol. 2001; 184: 489-96

(3) Flenady et al for Stillbirths Series steering committee. Stillbirths: the way forward in high-income countries. Lancet 2011; 377: 1703-1717

Competing interests: None declared

Mark Sillender, Consultant obstetrician & gynaecologist

Kaleeya & Fremantle Hospitals, Fremantle, Western Australia

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It is well known that very pre-term babies experience disadvantages in health outcomes in later life. Boyle et al. demonstrate that this is also the case for more mature pre-term babies. These findings confirm what life course epidemiology (see e.g. Kuh & Ben-Shlomo 2004) has postulated for a long time - that prenatal exposures and perinatal health contribute substantially to health in adult life. But what are the underlying mechanisms?

We would like to highlight one factor that could help to interpret the results of Boyle et al. In a recent study on the risk of stillbirth in different ethnic groups in Germany (Reeske et al. 2011) we found that low birth weight relative to gestational age contributed to a higher risk of unfavorable birth outcomes: babies from specific ethnic groups born with a low birth weight at regular gestational age (>=37 weeks) had an elevated risk of stillbirth. Small size or low weight for gestational age are predictors for intrauterine growth restriction (IUGR). IUGR increases the risk of unfavorable pre- and perinatal outcomes as well as chronic diseases in later life. Data on birth weight provide – with some limitations – Information about the physical development in relation to the gestational age. Children born with a low birth weight for their gestational age constitute a risk group for health disadvantages in later life. Including data on birth weight relative to gestational age in the analyses might explain some of the health differences that Boyle et al. found at age 3 and 5 years. We suggest that in future studies the effects of gestational age are analysed in combination with factors such as birth weight.

References

Kuh D & Ben-Shlomo Y. A life course approach to chronic disease epidemiology. Oxford University Press: Oxford 2004.

Reeske A, Kutschmann M, Razum O, Spallek J: Stillbirth differences according to regions of origin: an analysis of the German perinatal database, 2004-2007. BMC Pregnancy and Childbirth 2011; 11:63.

Competing interests: None declared

Jacob Spallek, Assistant Prof.

Anna Reeske, Oliver Razum

School of Public Health, Bielefeld University, Universitätsstraße 25, 33615 Bielefeld, Germany

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The height and weight at 3 and 5 years of age may also be dependent on food intake and physical activity apart from gestational age at birth, so their confounding should have been adjusted. Moreover, height is largely heritable1. According to one other study, inequalities in child's growth, although relatively small in magnitude, persist in England. These were fully explained by maternal and paternal reported height2. In other words, heights of parents, their growth pattern and velocity, all determine children’s growth pattern. Intelligence level/cognitive development is important aspect and should have been determined as well.

References:

1. Perola M, Sammalisto S, Hiekkalinna T, Martin NG, Visscher PM, et al. Combined genome scans for body stature in 6,602 European twins: evidence for common Caucasian loci. PLoS Genet. 2007;3:e97.

2. Galobardes B, McCormack VA, McCarron P, Howe LD, Lynch J, Lawlor DA, Smith GD. Social inequalities in height: persisting differences today depend upon height of the parents. PLoS One. 2012;7(1):e29118. Epub 2012 Jan 6.

Competing interests: None declared

Neeru Gupta, Scientist E

KK Jani

Indian Council of Medical Research, V Ramalingaswamy Bhawan, Ansari Nagar, New Delhi-110029

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Premature infants and preterm births carry a risk for developing asthma and respiratory diseases in later life. This study gives proof that gestational age at birth can influence the health of the child later with sociological and economical consequences. The statistics shows that the subjects included in the study were more or less equally distributed in different income groups. Rather the percentage of children represent more in the middle and higher income group. The development of respiratory diseases in these children in general and asthma in particular put the children on steroid therapy. Such a therapy makes them drug dependent with long term side effects. But a few studies have shown recently that these children or children with asthma or respiratory diseases have lower Vitamin D levels 1, and also our data reveal the same (unpublished). One of the factors that is attributed to such reduced vitamin D levels is wrapping the children fully in a cloth, preventing them gaining access to sun light. Children living in countries with poor sunlight due to a long winter can also have low vitamin D levels. Do the authors think vitamin D supplementation will help improve their health status?

Daniel A. S, Yong Z, James R. M, Pia J. H, Elena G, Donald Y.M. L,Decreased serum vitamin D levels in children with asthma are associated with increased corticosteroid use.The Journal of Allergy and Clinical Immunology 2010;125,:995-1000

dhastagir sheriff

Competing interests: None declared

dhastagir S sheriff, Professor

Faculty of Medicine,. Benghazi University, Benghazi

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