Appendix B: Outcomes for different places of birth – by BMI at booking | Intrapartum care | Guidance

Guidance

Appendix B: Outcomes for different places of birth – by BMI at booking

**Table B1 Nulliparous and multiparous women with planned birth in an obstetric unit: how body mass index (BMI) may affect the rate of stillbirth, neonatal death or the baby needing neonatal care**
Body mass index (BMI) at booking (kg/m²)	Nulliparous women: Average rate of stillbirth, neonatal death or baby needing neonatal care	Multiparous women: Average rate of stillbirth, neonatal death or baby needing neonatal care
18.5 to 24.9	36 per 1,000 (so this does not happen in about 964 pregnancies per 1,000)	17 per 1,000 (so this does not happen in about 983 pregnancies per 1,000)
25 to 29.9	No difference compared with women with a BMI 18.5 to 24.9 kg/m²	No difference compared with women with a BMI 18.5 to 24.9 kg/m²
30 to 35	No difference compared with women with a BMI 18.5 to 24.9 kg/m²	No difference compared with women with a BMI 18.5 to 24.9 kg/m²
More than 35	67 per 1,000 (so this does not happen in about 933 pregnancies per 1,000). This is an average increase of 31 per 1,000 compared with women with a BMI 18.5 to 24.9 kg/m²(so for about 969 pregnancies per 1,000, the outcome was the same)	27 per 1,000 (so this does not happen in about 973 pregnancies per 1,000). This is an average increase of about 10 per 1,000 compared with women with a BMI 18.5 to 24.9 kg/m²(so for about 990 pregnancies per 1,000, the outcome was the same)

**Table B2 Nulliparous women with planned birth in an alongside midwifery unit: how BMI above or below 35 kg/m2 may affect the rate of caesarean birth and postpartum haemorrhage**
Body mass index (BMI) at booking (kg/m²)	Average rate of intrapartum caesarean birth (category 1, 2 or 3)	Average rate of emergency caesarean birth (category 1 or 2)	Average rate of postpartum haemorrhage
35 or less	82 per 1,000 (so this does not happen in about 918 pregnancies per 1,000)	65 per 1,000 (so this does not happen in about 935 pregnancies per 1,000)	17 per 1,000 (so this does not happen in about 983 pregnancies per 1,000)
More than 35	138 per 1,000 (so this does not happen in about 862 pregnancies per 1,000). This is an average increase of 56 per 1,000 compared with women with a BMI less than 35 kg/m² (so for about 944 pregnancies per 1,000, the outcome was the same)	122 per 1,000 (so this does not happen in about 878 pregnancies per 1,000). This is an average increase of 57 per 1,000 compared with women with a BMI less than 35 kg/m² (so for about 943 pregnancies per 1,000, the outcome was the same)	51 per 1,000 (so this does not happen in about 949 pregnancies per 1,000). This is an average increase of 34 per 1,000 compared with women with a BMI less than 35 kg/m² (so for about 966 pregnancies per 1,000, the outcome was the same)

**Table B3 Multiparous women with planned birth in an alongside midwifery unit: how BMI above or below 35 kg/m2 may affect the rate of caesarean birth and postpartum haemorrhage**
Body mass index (BMI) at booking (kg/m²)	Average rate of intrapartum caesarean birth (category 1, 2 or 3)	Average rate of emergency caesarean birth (category 1 or 2)	Average rate of postpartum haemorrhage
35 or less	7 per 1,000 (so this does not happen in about 993 pregnancies per 1,000)	5 per 1,000 (so this does not happen in about 995 pregnancies per 1,000)	20 per 1,000 (so this does not happen in about 980 pregnancies per 1,000)
More than 35	No difference compared with women with a BMI 35 kg/m²or less	No difference compared with women with a BMI 35 kg/m²or less	No difference compared with women with a BMI 35 kg/m²or less

**Table B4 Nulliparous and multiparous women: how BMI may affect the rate of transfer from home to an obstetric unit**
Body mass index (BMI) at booking (kg/m²)	Nulliparous women; Average rate of transfer from home to an obstetric unit	Multiparous women: Average rate of transfer from home to an obstetric unit
18.5 to 24.9	448 per 1,000 (so this does not happen in about 552 pregnancies per 1,000)	102 per 1,000 (so this does not happen in about 898 pregnancies per 1,000)
25 to 29.9	No difference compared with women with a BMI 18.5 to 24.9 kg/m²	No difference compared with women with a BMI 18.5 to 24.9 kg/m²
30 to 35	No difference compared with women with a BMI 18.5 to 24.9 kg/m²	145 per 1,000 (so this does not happen in about 855 pregnancies per 1,000). This is an average increase of 43 per 1,000 compared with women with a BMI 18.5 to 24.9 kg/m²(so for about 957 pregnancies per 1,000, the outcome was the same)

**Table B5 All women with planned birth in an obstetric unit: how BMI may affect the rate of caesarean birth or the rate of stillbirth, neonatal death or the baby needing neonatal care**
Body mass index (BMI) at booking (kg/m²)	Average rate of intrapartum caesarean birth (category 1, 2 or 3)	Average rate of stillbirth, neonatal death or the baby needing neonatal care	Average rate of birth with forceps or ventouse
Less than 18.5	No difference compared with women with a BMI 18.5 to 24.9 kg/m²	No difference compared with women with a BMI 18.5 to 24.9 kg/m²	No difference compared with women with a BMI 18.5 to 24.9 kg/m²
18.5 to 24.9	95 per 1,000 (so this does not happen in about 905 pregnancies per 1,000)	28 per 1,000 (so this does not happen in about 972 pregnancies per 1,000)	156 per 1,000 (so this does not happen in about 844 pregnancies per 1,000)
25 to 29.9	123 per 1,000 (so this does not happen in about 877 pregnancies per 1,000). This is an average increase of 28 per 1,000 compared with women with a BMI 18.5 to 24.9 kg/m²(so for about 972 pregnancies per 1,000, the outcome was the same)	No difference compared with women with a BMI 18.5 to 24.9 kg/m²	No difference compared with women with a BMI 18.5 to 24.9 kg/m²
30 to 35	133 per 1,000 (so this does not happen in about 867 pregnancies per 1,000). This is an average increase of 38 per 1,000 compared with women with a BMI 18.5 to 24.9 kg/m²(so for about 962 pregnancies per 1,000, the outcome was the same)	No difference compared with women with a BMI 18.5 to 24.9 kg/m²	No difference compared with women with a BMI 18.5 to 24.9 kg/m²
More than 35	137 per 1,000 (so this does not happen in about 863 pregnancies per 1,000). This is an average increase of 42 per 1,000 compared with women with a BMI 18.5 to 24.9 kg/m²(so for about 958 pregnancies per 1,000, the outcome was the same)	51 per 1,000 (so this does not happen in about 949 pregnancies per 1,000). This is an average increase of 23 per 1,000 compared with women with a BMI 18.5 to 24.9 kg/m²(so for about 977 pregnancies per 1,000, the outcome was the same)	85 per 1,000 (so this does not happen in 915 pregnancies per 1,000). This is a decrease of 71 per 1,000 compared with women with a BMI 18.5 to 24.9 kg/m²(so for about 929 pregnancies per 1,000, the outcome was the same)

Source: evidence review A: impact of BMI on choice of place of birth. For more details on risks identified in different settings, see evidence review A.

For more information of the categories of caesarean birth, see the NICE guideline on caesarean birth.

The data in these tables are based on a population of women of mixed ethnicity. No data was available for different ethnic groups. New reference ranges defining overweight and obesity for non-pregnant women from different ethnic groups are available in the NICE guideline on obesity, but the correlation of these revised ranges with intrapartum risks for women and their babies is not known.