Infant male sex as a risk factor for shoulder dystocia but not for cephalopelvic disproportion: an independent or confounded effect?

Reconsidering the developmental origins of adult disease paradigm: The 'metabolic coordination of childbirth' hypothesis

In uncomplicated pregnancies, birthweight is inversely associated with adult non-communicable disease (NCD) risk. One proposed mechanism is maternal malnutrition during pregnancy. Another explanation is that shared genes link birthweight with NCDs. Both hypotheses are supported, but evolutionary perspectives address only the environmental pathway. We propose that genetic and environmental associations of birthweight with NCD risk reflect coordinated regulatory systems between mother and foetus, that evolved to reduce risks of obstructed labour. First, the foetus must tailor its growth to maternal metabolic signals, as it cannot predict the size of the birth canal from its own genome. Second, we predict that maternal alleles that promote placental nutrient supply have been selected to constrain foetal growth and gestation length when fetally expressed. Conversely, maternal alleles that increase birth canal size have been selected to promote foetal growth and gestation when fetally expressed. Evidence supports these hypotheses. These regulatory mechanisms may have undergone powerful selection as hominin neonates evolved larger size and encephalisation, since every mother is at risk of gestating a baby excessively for her pelvis. Our perspective can explain the inverse association of birthweight with NCD risk across most of the birthweight range: any constraint of birthweight, through plastic or genetic mechanisms, may reduce the capacity for homeostasis and increase NCD susceptibility. However, maternal obesity and diabetes can overwhelm this coordination system, challenging vaginal delivery while increasing offspring NCD risk. We argue that selection on viable vaginal delivery played an over-arching role in shaping the association of birthweight with NCD risk.

Born before arrival in NSW, Australia (2000-2011): a linked population data study of incidence, location, associated factors and maternal and neonatal outcomes

OBJECTIVES

To determine incidence, associated factors, outcomes and geographical occurrence of born before arrival (BBA) in New South Wales, Australia.

DESIGN

A linked population data study involving population-based surveillance systems was undertaken for the years 2000-2011.

SETTING

New South Wales, Australia.

PARTICIPANTS

All women who underwent BBA compared with women who birthed in hospital/birth centre settings.

RESULTS

During the time period, there were 1 097 653 births and a BBA rate of 4.6 per 1000 births. The BBA rate changed from 4.2 to 4.8 per 1000 births over time (p=0.06). Neonates BBA were more likely to be premature (12.5% compared with 7.3%), of lower birth weight (209.8 g mean difference) and/or be admitted to a special care nursery or neonatal intensive care unit (20.6% compared with 15.6%). The perinatal mortality rate was significantly higher in the BBA cohort (34.6 compared with 9.3 per 1000 births). Women in the BBA cohort were more likely to be in the lowest socioeconomic decile, multiparous, have higher rates of smoking (30.5% compared with 13.8%) and more likely to suffer a postpartum haemorrhage requiring transfusion than the non-BBA cohort (1.5% compared with 0.7%). The most commonly occurring complications for neonates were suspected infection (6.9%), hypothermia (6.9%), respiratory distress (5.4%), congenital abnormality (4.0%) and neonatal withdrawal symptoms (2.4%). BBA more commonly occurred in geographical areas where the distance to a maternity unit is >2 hours drive and in coastal regions where there is also a high rate of homebirth.

CONCLUSION

BBA occurs more frequently in multiparous women of lower socioeconomic status. There potentially is an effect of geography on the occurrence of BBA, as geographical area of high homebirth and BBA coexists, indicating that freebirth followed by an unplanned transfer to hospital may be occurring.

Trends and risk factors for severe perineal trauma during childbirth in New South Wales between 2000 and 2008: a population-based data study

OBJECTIVES

To determine trends and risk factors for severe perineal trauma between 2000 and 2008.

DESIGN

This was a population-based data study.

SETTING

New South Wales, Australia.

PARTICIPANTS

510 006 women giving birth to a singleton baby during the period 2000-2008.

MAIN OUTCOME MEASURES

Rates of severe perineal trauma between 2000 and 2008 and associated demographic, fetal, antenatal, labour and delivery events and factors.

RESULTS

There was an increase in the overall rate of severe perineal trauma from 2000 to 2008 from 1.4% to 1.9% (36% increase). Compared with women who were intact or had minor perineal trauma (first-degree tear, vaginal graze/tear), women who were primiparous (adjusted OR (AOR) 1.8 CI (1.65 to 1.95), were born in China or Vietnam (AOR 1.1 CI (1.09 to 1.23), gave birth in a private hospital (AOR 1.1 CI (1.03 to 1.20), had an instrumental birth (AOR 1.8 CI (1.65 to 1.95) and male baby (AOR 1.3 CI (1.27 to 1.34) all had a significantly higher risk of severe perineal trauma. Only giving birth to a male baby, adjusted for birth weight (AOR 1.5 CI (1.44 to 1.58), remained significant, when women with severe perineal trauma were compared with all other women not experiencing severe perineal trauma. This association increased over the study period.

CONCLUSIONS

To our knowledge, this is the first time that having a male baby has been found to exert such a strong independent risk for severe perineal trauma and the increasing significance of this in recent years needs further exploration.