Results
Linkage of Data
During the study period, 240,400 women who had no previous caesarean section, a singleton pregnancy, and a spontaneous onset of labour between 37 and 42 weeks’ gestation were recorded in the national perinatal register. In the LEMMoN study, 706 women met these criteria and had severe acute maternal morbidity after the onset of labour (27.7% of all women with severe acute maternal morbidity) (Figure 1). Of these, 56 could not be linked to data in the perinatal register (7.9%). Women with severe acute maternal morbidity who were linked to the perinatal register did not differ significantly for type of severe acute maternal morbidity, parity, and ethnicity from those that were not linked to the register.
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Figure 1.
Flow of births between August 2004 and July 2006.
Of the total linked data, 10,101 (4.2%) women were referred during or after labour but were missing the national perinatal database-1 form and 52 of the women in this category had severe acute maternal morbidity. Compared with all women who were referred during or after labour these women were more likely to be parous (31.2% v 30.0%) and of Dutch ethnicity (83.4% v 78.7%). There were no significant differences between these groups in incidence and type of severe acute maternal morbidity.
The linked dataset contained information on 230 299 women, of whom 598 (2.6 per 1000) had severe acute maternal morbidity. Of these, 172 973 started labour in primary care (severe acute maternal morbidity, n=364), and for 439 women (severe acute maternal morbidity, n=1) the level of care at the start of labour was unknown.
Study Population
Of the women in primary care at the onset of labour, planned place of birth was unknown for 18,070 and these women were not included in the analyses (Figure 1). Another 2112 women were excluded because they had a “medium risk” indication. Of these, 1248 (59.1%) had a history of retained placenta or postpartum haemorrhage and the others had various indications such as “no prenatal care” and “use of medication (not further specified).” An additional 6039 women were not included because they were referred for prolonged ruptured membranes without contractions.
Of the remaining 146,752 women in primary care at the onset of labour, 92,333 (62.9%) had a planned home birth and 54 419 (37.1%) had a planned hospital birth ( Table 1 ). Women with planned home birth compared with those with planned hospital birth were more likely to be parous, less likely to give birth between 37+0 and 37+6 weeks’ gestation, and more likely to give birth between 41+0 and 41+6 weeks; they were less often younger than 25 years, more often aged between 25 and 34 years, more often of Dutch origin, and less often of a lower socioeconomic position.
Adverse Maternal Outcomes
Of all women included in the analyses, 288 (2.0 per 1000) had severe acute maternal morbidity ( Table 2 ). Among planned home births, severe acute maternal morbidity occurred in 141 women (1.5 per 1000) and among planned hospital births in 147 women (2.7 per 1000). Most of the affected women had a blood transfusion of four or more packed cells. Other causes were rare. Postpartum haemorrhage was the most common adverse maternal outcome and this occurred among 2699 (29.2 per 1000) planned home births and among 2172 (39.9 per 1000) planned hospital births.
Adverse outcomes were less common among planned home births than among planned hospital births, but differences were only statistically significant for parous women ( Table 3 ). Among nulliparous women outcomes for planned home versus planned hospital births were: severe acute maternal morbidity adjusted odds ratio 0.77 (95% confidence interval 0.56 to 1.06) and relative risk reduction 25.7% (95% confidence interval -0.1% to 53.5%), blood transfusion of four or more packed cells 0.90 (0.65 to 1.27) and 14.5% (-14.7% to 45.8%), postpartum haemorrhage 0.92 (0.85 to 1.00) and 0.5% (-6.8% to 7.9%), and manual removal of placenta 0.91 (0.83 to 1.00) and 2.8% (-6.1% to 11.8%). Among parous women outcomes for planned home versus hospital births were: severe acute maternal morbidity adjusted odds ratio 0.43 (95% confidence interval 0.29 to 0.63), blood transfusion of four or more packed cells 0.45 (0.30 to 0.68), postpartum haemorrhage 0.50 (0.46 to 0.55), and manual removal of placenta 0.41 (0.36 to 0.47).
Sensitivity Analyses and Adjustment for Medical Interventions
Sensitivity analyses showed similar results for all outcomes in Table 3 (data not shown). In some of the sensitivity analyses, differences just reached statistical significance that did not in the main analyses. For example, for the comparison of severe acute maternal morbidity, if only women without discrepancies in onset of labour between the data forms from primary and secondary care were selected the adjusted odds ratio for planned home versus planned hospital birth in nulliparous women was 0.63 (95% confidence interval 0.44 to 0.88) and in parous women was 0.46 (0.30 to 0.69). If onset of labour was based on the national perinatal database-1 form only, the differences in severe acute maternal morbidity, postpartum haemorrhage, and manual removal of placenta became significant for nulliparous women: 0.72 (0.53 to 0.99), 0.90 (0.83 to 0.97), and 0.88 (0.80 to 0.96), respectively.
Fewer women with planned home births compared with planned hospital births received augmentation of labour (nulliparous women 22.9% v 27.5% and parous women 3.4% v 7.8%, respectively) and had an operative delivery (nulliparous women 23.1% v 24.7% and parous women 1.6% v 3.2%). The comparison of severe acute maternal morbidity controlled for augmentation of labour and operative delivery for planned home versus planned hospital births among nulliparous women gave an adjusted odds ratio of 0.80 (0.58 to 1.10), which is an increase of 3.9% in odds ratio. For parous women the adjusted odds ratio for severe acute maternal morbidity after controlling for these interventions was 0.47 (0.32 to 0.69), which is an increase of 9.3% in odds ratio.