With the resurgence of interest in planned out-of-hospital deliveries in the past 30 years, there has been much debate about the safety of home deliveries. The results of studies comparing neonatal and perinatal mortality associated with intended home deliveries and with hospital deliveries have been conflicting, and these studies often have not been able to fully separate the influence of delivery location from other determinants of pregnancy outcome with which delivery location may be associated. Studies done in Missouri, North Carolina, and Australia1–3 observed an elevated risk of neonatal death in intended home births delivered by professional providers, whereas a study done in Washington State on intended home births found no increased risk of neonatal mortality.4 All four studies included comparison groups of hospital births attended by health professionals. However, only one of the studies sought to differentiate whether a hospital birth was intended to occur at home at the onset of labor.
The objective of this study was to evaluate the risk of neonatal death for intended home deliveries by professional providers compared with that of intended hospital deliveries. We also evaluated whether planned home deliveries were associated with an altered risk of postneonatal death, neonatal respiratory distress, very low Apgar score at 5 minutes, prolonged labor, and postpartum hemorrhage.
MATERIALS AND METHODS
We conducted a population-based cohort study using Washington State birth certificate data from 1989 to 1996. The birth certificate data were linked to the Washington State infant death certificates to identify cases of neonatal death and postneonatal death. Other outcomes such as postpartum bleeding, prolonged labor, neonatal respiratory distress (defined as postdelivery ventilation for more than 30 minutes), and a very low Apgar score (≤3) at 5 minutes were identified through information provided by birth certificates. Because Washington State birth certificates do not identify which home births are planned, we defined planned home births as those singleton newborns of at least 34 weeks' gestation who were delivered at home and who had a midwife, nurse, or physician listed as either the birth attendant or certifier on the birth certificate (if an attendant is not listed on the birth certificate, then the person listed as the certifier attended the delivery). In addition, singleton newborns with gestational age of at least 34 weeks who were born after transfer from home to a medical facility were considered to be planned home births if their birth certificates indicated that delivery was initially attempted at home by a health care professional. The gestational age of an infant was recorded by the attendant of record at each birth. The cohort of intended home births consisted of 7518 newborns (approximately 1% of all deliveries in Washington State during the study period), 7019 of whom were born at home, and 499 of whom were born in hospitals after transfer from home. For comparison, the birth certificate records of 14,038 singletons who were of at least 34 weeks' gestation and born in hospitals (with no indication on the birth certificate that the delivery was initially attempted at home) were selected at random, except for frequency matching by year of birth to the infants intended to be born at home. To minimize misclassification of intended and unintended home births, the main analysis was confined to births in which there were no recorded pregnancy-related complications (6133 home births, 10,593 hospital births), because it is unlikely that women with one or more of these complications actually intended to deliver at home (Figure 1). Two hundred seventy-nine of the 6133 home deliveries were births attempted at home before transfer to a hospital. Pregnancy-related complications included 18 specific diagnoses: anemia (hematocrit <30% or hemoglobin <10 mg/dL), cardiac disease, acute or chronic lung disease, diabetes, polyhydramnios, oligohydramnios, genital herpes, hemoglobinopathy, chronic hypertension, pregnancy-induced hypertension, eclampsia, incompetent cervix, previous preterm or small for gestational age infant, macrosomia in a previous birth (>4000 g), renal disease, Rh sensitization, syphilis, and hepatitis B infection. Secondary analyses were performed after further restricting the study subjects to infants weighing at least 2500 g at birth or of at least 37 weeks' gestation, again in an effort to minimize the possibility of including births at home that were high risk and thus not planned to take place there.
To assess the influence of planned location of birth apart from that of other factors, the relative risk (RR) for each outcome was estimated by stratified analysis using the Cochran Mantel-Haenszel method. All biostatistical calculations were done through use of SAS software (6.12 TS050; SAS Institute, Cary, NC). Variables that were considered as potential confounders or effect modifiers included maternal age (10–19 years, 20–29 years, 30+ years), race (white, black, Asian, and other), marital status (married, unmarried), educational level (high school or less, more than high school), payer status (indigent, insured/self-paying), smoking (yes, no), county of birth (King County, Pierce County, Snohomish County, Spokane County, and other counties), residence (urban, rural), prenatal care (initial visit during first, second, or third trimester), parity (0, 1+), and birth weight (less than 2500 g, 2500+ g). A factor was considered in the final model if it altered the crude relative risk by at least 10%.
Analysis of Washington State birth certificate data from unidentified participants was approved for research purposes through the University of Washington institutional review board and in agreement with the Washington State Department of Health.
Relative to women intending to deliver in hospital, those intending to deliver at home were, on average, older, more likely to be married, white, nonsmokers, and parous (Table 1). They also tended to be more highly educated; however, data on education were not collected for mothers giving birth before 1992 (almost 50% of both of the home birth and hospital birth cohorts). Women intending to deliver at home were slightly less likely to reside in an urban area, to live in King County, to have initiated prenatal care during the first trimester, and to deliver infants weighing less than 2500 g. Among women who had birth certificate data on ultrasound use, 34% of those who chose home births had at least one ultrasound done during their pregnancies as compared with 35% of the women who chose hospital births (data not shown). Women who intended to deliver at home were also less likely to be indigent as identified by payer status, though data on payer status was missing for more than 30% of women.
Infants born to women who planned to deliver at home had lower Apgar scores at 5 minutes than infants born to women who planned to deliver in hospitals, and a greater proportion of these infants died during the neonatal period or had respiratory distress at delivery (Table 2). The proportions of infants dying in the postneonatal period were similar for the two groups. Compared with women delivering in hospitals, a slightly higher percentage of women with planned home deliveries had prolonged labor and postpartum bleeding.
The risk of neonatal death was almost twice as high for infants born to women intending to deliver at home as for infants born to women delivering in hospitals (RR 1.99, 95% confidence interval [CI] 1.06, 3.73), after adjustment for parity (Table 3). Adjustment for either maternal education or payer status led to a very slight increase in the RR. The association between place of intended delivery and neonatal death was not affected appreciably by adjustment for any other potential confounding factors described above. Similar findings were seen when further restricting the analysis to infants of at least 37 weeks' gestation (RR 2.09, 95% CI 1.09, 3.97, after adjusting for maternal age) (Table 3) and to infants with birth weight of at least 2500 g.
The association between intent to deliver at home and neonatal death was particularly strong in previously nulliparous women (RR 2.73, 95% CI 1.06, 7.06). This relative risk remained elevated when the analysis was further restricted to infants with gestational age of 37 weeks or greater (RR 2.99, 95% CI 1.12, 7.94).
Infants born to women intending a home delivery were more than twice as likely to have a very low Apgar score at 5 minutes (RR adjusted for maternal age 2.31, 95% CI 1.29, 4.16) (Table 3). The size of the relative risk was similar for infants born to nulliparous or to parous women.
Infants born to nulliparous women who intended to deliver at home appeared to have an increased risk of neonatal respiratory distress relative to infants of other nulliparous women (RR 2.79, 95% CI 0.98, 7.93). Restriction of the analysis to infants of at least 37 weeks' gestation gave a similar result (RR 3.17, 95% CI 1.07, 9.42).
Nulliparous women intending a home delivery were more likely to have prolonged labor (RR 1.73, 95% CI 1.28, 2.34) and to have postpartum hemorrhage (RR 2.76, 95% CI 1.74, 4.36) than nulliparous women delivering in hospitals. Similar results were observed when further restricting the analysis to infants of at least 37 weeks' gestation. No association between these two maternal complications and intended location of delivery was seen among parous women; among pregnancies of at least 34 weeks' gestation, the respective relative risks were 1.09 (95% CI 0.67, 1.77) and 1.05 (95% CI 0.68, 1.60). Among pregnancies of at least 37 weeks' gestation, the respective relative risks were 1.07 (95% CI 0.66, 1.74) and 0.97 (95% CI 0.63, 1.50).
Deaths from congenital heart disease and respiratory distress, two causes that might be expected to be amenable to prevention in the hospital setting, occurred with a relatively higher frequency among infants whose births were planned at home (Table 4).
Although mothers intending to deliver infants at home were more likely to be at least 20 years old, married, nonsmokers, and insured than mothers who delivered in hospitals, planned home births were associated with an elevated risk of neonatal mortality and very low Apgar score at 5 minutes in this study. Planned home births were also associated with increased risk of prolonged labor and postpartum bleeding among nulliparous women. The incidence of neonatal mortality was 3.5 out of 1000 live births for planned home births and 1.7 out of 1000 live births for hospital births. Planned home births were associated with a two-fold increase in the risk of having a very low Apgar score at 5 minutes, a 50% increase in the risk of prolonged labor, and a 58% increase in the risk of postpartum bleeding.
This study has several limitations that are related to the reliance on birth certificate data. These include the potential for misclassifying unplanned home births as planned home births and for misclassifying various outcomes and covariates. In addition, data were missing for some potential confounders and effect modifiers. Several of the outcomes of interest were relatively uncommon, leading to results with wide confidence intervals. Lastly, the specific content of prenatal care for each pregnancy and its use for screening or for diagnosis of adverse neonatal and maternal outcomes could not be ascertained through use of birth certificates.
In previous studies, neonatal mortality among unplanned home births was high (73 of 1000 to 120 of 1000 live births).2,5 A proportion of home births are unplanned, and a large number of unplanned home births occur in women who have complicated pregnancies and/or who deliver preterm infants.5 Therefore, misclassification of any unplanned home births as planned home births in this study would result in inflated risk estimates of neonatal mortality and other outcomes for planned home births.6 We sought to minimize misclassification of intended location of delivery in this study by excluding infants born at less than 34 weeks' gestation and by excluding births in which complications were identified during pregnancy. This source of misclassification likely was further decreased when we restricted the analysis to infants with birth weight of at least 2500 g or to infants of at least 37 weeks' gestation. Because information on birth weight was missing more often for home than hospital births, we gave primary emphasis to the analyses that did not consider birth weight.
Several of the outcomes in this study may have been misclassified, namely respiratory distress requiring assisted ventilation for more than 30 minutes, prolonged labor, and postpartum hemorrhage. The likelihood of misclassification might be greater in a home setting than in a hospital, but the magnitude and direction of any such bias cannot be predicted and so caution should be used when interpreting the results for these outcomes.
Misclassification of potential confounders and effect modifiers will occur to the extent that ascertainment and reporting of these factors is incomplete on birth certificates. A study in Tennessee found that demographic characteristics and birth weight were accurately obtained on birth certificates, in contrast to data concerning complications of labor and delivery, abnormal conditions of neonates, and congenital anomalies.7 However, there is no reason to expect that there would be a difference in the ascertainment or reporting of these factors between home and hospital births in which professional providers were present.
Because Washington State birth certificates did not solicit information on maternal education or payment source before 1992, we were not able to fully assess the influence of these two factors on the association between planned location of birth and the outcomes of interest. That influence is likely to be minimal, however, because none of the risk estimates of the outcomes changed appreciably after restriction of the analysis to births occurring during 1992–1996 that permitted adjustment for these factors. Results of previous studies suggest that planned home births are not associated with an increased risk of a having a low Apgar score at 5 minutes.4,8–13 However, these studies have defined a “low” score as less than 7 or 8. Because there is considerable potential for subjective variation in assessment of Apgar scores between 5 and 8, it is possible that this outcome was misclassified. In addition, the clinical importance of Apgar scores between 5 and 8 on other infant outcomes is unclear. We defined a low Apgar score as one that was less than or equal to 3 to minimize potential misclassification and also because Apgar scores less than or equal to 3 are more strongly associated with adverse outcomes.
The safety of intended home births remains controversial. In one population-based cohort study of 3067 intended home deliveries in Missouri, there was a twofold increase in the overall risk of neonatal death in babies delivered at home compared with hospital deliveries attended by physicians.3 Providers of all levels of training attended the intended home deliveries, with higher risk estimates associated with lower levels of attendant training. A second cohort study of 934 home deliveries in North Carolina observed that the risk of neonatal death was four of 1000 live births in planned home deliveries attended by lay midwives, 30 of 1000 live births when the home delivery was attended by a provider other than a physician or lay midwife, and 12 of 1000 live births that took place in hospitals.2 Thus, there was a suggestion in both studies that the level of training of the home birth attendant may partly determine the outcome of the birth. However, neither study adjusted for antenatal complications of pregnancy or for low birth weight, both of which are more common among hospital births. Failure to adjust for one or both of these variables would be expected to result in artificially low estimates of the risk of planned home births when compared with hospital birth cohorts.14,15 An Australian study, comparing death rates of intended home births where the neonates weighed 2500 grams or more to national Australian rates for infants of comparable birth weight, observed a 1.6-fold increase in the former group (95% CI 1.1, 2.4).1 A fourth study comparing 6456 out-of-hospital births attended by licensed midwives to 23,956 hospital births attended by physicians in Washington State during 1980–1990 observed that out-of-hospital deliveries were associated with a comparable rate of neonatal death as hospital deliveries.4 This study addressed possible confounding by maternal age, ethnicity, marital status, occupation, parity, adequacy of prenatal care, classification of residence, and pregnancy-related complications on neonatal mortality in both groups. However, information allowing more accurate determination of the intended location of delivery became available from Washington State birth certificates only at the end of the period included in this study, limiting the ability of the authors to remove potential bias from the misclassification of infants of planned home deliveries who were born after transfer from home to medical facilities as hospital births.
The proportion of physicians attending home births in this cohort was too small (7.6% of all home births) to examine pregnancy outcomes for this group alone. Unlike the previous study done in Washington State, ours did not address the influences of different types of non-physician attendants in the outcomes of home delivery because we could not readily verify this information on the Washington State birth certificates. A study done by Myers et al showed that birth certificate data correctly identified attendant type for out-of-hospital births 30% of the time.5 The major source of attendant misclassification was between the various types of midwives. The proportion of misclassification between professional and nonprofessional providers was not assessed.
The results of our study suggest that planned home births are associated with an increased risk of adverse neonatal and maternal outcomes, particularly among nulliparous women. Nonetheless, more light needs to be shed on this controversial topic before practitioners and expectant parents can be fairly counseled about the safety of planned home births. Future observational studies using a study design that accurately assesses the intention to deliver at home, adverse pregnancy outcomes, and relevant confounding factors are needed.
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