National Women's Annual Clinical Report 2010

50
45
40
35
30
25
20
15
10
5
0
%
European Maori Pacific Asian
35
Figure 40: Caesarean section rate by BMI and by ethnicity among nulliparous mothers (no data
point plotted if denominator < 30)
%
30
25
20
15
10
5
0
European Maori Pacific Asian
35
Figure 41: Operative vaginal birth rate by BMI and by ethnicity among nulliparous mothers (no
data point plotted if denominator < 30)
Operative vaginal birth rates in nulliparous women are generally lower in obese women
compared with those with normal BMI due to higher rates of Caesarean section, however
differences between ethnicities are also present (e.g. lower operative vaginal birth rates in
obese Pacific nulliparous women who also have a lower Caesarean section rate and higher
spontaneous vaginal birth rate than women who are obese in other ethnicities). Further
multivariate analyses are needed before conclusions can be drawn.
The data in the three preceding figures can be used to provide some guidance to women
and carers about the likely mode of birth in nulliparous women according to BMI categories.
The mode of birth will be influenced by mode of onset of labour and presence of pregnancy
complications as well as other factors e.g. obese women have elevated rates of induction of
labour including indications such as diabetes, hypertensive disease, and possibly prolonged
pregnancy.
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