Recent trends and patterns in cesarean and vaginal birth after cesarean (VBAC) deliveries in the United States.

Cesarean delivery is the most common major surgical procedure for women in the United States, with 1.4 million surgeries annually. In 2008, nearly one-third (32.3%) of US births were by cesarean delivery. Cesarean delivery rates have increased rapidly in the United States in recent years because of an increasing primary cesarean delivery rate and a declining vaginal birth after cesarean (VBAC) rate. In 2007, the VBAC rate was 8.3% in a 22-state reporting area. The US VBAC rate was lowest among 14 industrialized countries; 3 countries had VBAC rates greater than 50%.

Trends and characteristics of home births in the United States by race and ethnicity, 1990-2006.

BACKGROUND: After a gradual decline from 1990 to 2004, the percentage of births occurring at home in the United States increased by 5 percent in 2005 and that increase was sustained in 2006. The purpose of the study was to analyze trends and characteristics in home births in United States by race and ethnicity from 1990 to 2006. METHODS: U.S. birth certificate data on home births were analyzed and compared with hospital births for a variety of demographic and medical characteristics. RESULTS: From 1990 to 2006, both the number and percentage of home births increased for non-Hispanic white women, but declined for all other race and ethnic groups. In 2006, non-Hispanic white women were three to four times more likely to have a home birth than women of other race and ethnic groups. Home births were more likely than hospital births to occur to older, married women with singleton pregnancies and several previous children. For non-Hispanic white women, fewer home births than hospital births were born preterm, whereas for other race and ethnic groups a higher percentage of home births than hospital births were born preterm. For non-Hispanic white women, two-thirds of home births were delivered by midwives. In contrast, for other race and ethnic groups, most home births were delivered by either physicians or "other" attendants, suggesting that a higher proportion of these births may be unplanned home births because of emergency situations. CONCLUSIONS: Differences in the risk profile of home births by race and ethnicity are consistent with previous research, suggesting that, compared with non-Hispanic white women, a larger proportion of non-Hispanic black and Hispanic home births represent unplanned, emergency situations.

Trends and characteristics of home and other out-of-hospital births in the United States, 1990-2006.

OBJECTIVES: This report examines trends and characteristics of out-of-hospital and home births in the United States. METHODS: Descriptive tabulations of data are presented and interpreted. RESULTS: In 2006, there were 38,568 out-of-hospital births in the United States, including 24,970 home births and 10,781 births occurring in a freestanding birthing center. After a gradual decline from 1990 to 2004, the percentage of out-of-hospital births increased by 3% from 0.87% in 2004 to 0.90% in 2005 and 2006. A similar pattern was found for home births. After a gradual decline from 1990 to 2004, the percentage of home births increased by 5% to 0.59% in 2005 and remained steady in 2006. Compared with the U.S. average, home birth rates were higher for non-Hispanic white women, married women, women aged 25 and over, and women with several previous children. Home births were less likely than hospital births to be preterm, low birthweight, or multiple deliveries. The percentage of home births was 74% higher in rural counties of less than 100,000 population than in counties with a population size of 100,000 or more. The percentage of home births also varied widely by state; in Vermont and Montana more than 2% of births in 2005-2006 were home births, compared with less than 0.2% in Louisiana and Nebraska. About 61% of home births were delivered by midwives. Among midwife-delivered home births, one-fourth (27%) were delivered by certified nurse midwives, and nearly three-fourths (73%) were delivered by other midwives. DISCUSSION: Women may choose home birth for a variety of reasons, including a desire for a low-intervention birth in a familiar environment surrounded by family and friends and cultural or religious concerns. Lack of transportation in rural areas and cost factors may also play a role.

Characteristics of planned and unplanned home births in 19 States.

OBJECTIVE: To estimate the differences in the characteristics of mothers having planned and unplanned home births that occurred at home in a 19-state reporting area in the United States in 2006. METHODS: Data are from the 2006 U.S. vital statistics natality file. Information on whether a home birth was planned or unplanned was available from 19 states, representing 49% of all home births nationally. Data were examined by maternal age, race or ethnicity, education, marital status, live birth order, birthplace of mother, gestational age, prenatal care, smoking status, state, population of county of residence, and birth attendant. We could not identify planned home births that resulted in a transfer to the hospital. RESULTS: Of the 11,787 home births with planning status recorded in the 19 states studied here, 9,810 (83.2%) were identified as planned home births. The proportion of all births that occurred at home that were planned varied from 54% to 98% across states. Unplanned home births are more likely to involve mothers who are non-white, younger, unmarried, foreign-born, smokers, not college-educated, and with no prenatal care. Unplanned home births are also more likely to be preterm and to be attended by someone who is neither a doctor nor a midwife and is listed as either "other" or "unknown." CONCLUSION: Planned and unplanned home births differ substantially in characteristics, and distinctions need to be drawn between the two in subsequent analyses. LEVEL OF EVIDENCE: III.

Recent trends in cesarean delivery in the United States.

KEY FINDINGS: Data from the Natality Data File, National Vital Statistics System. The cesarean rate rose by 53% from 1996 to 2007, reaching 32%, the highest rate ever reported in the United States. From 1996 to 2007, the cesarean rate increased for mothers in all age and racial and Hispanic origin groups. The pace of the increase accelerated from 2000 to 2007. Cesarean rates also increased for infants at all gestational ages; from 1996 to 2006 preterm infants had the highest rates. Cesarean rates increased for births to mothers in all U.S. states, and by more than 70% in six states from 1996 to 2007.

Neonatal mortality risk for repeat cesarean compared to vaginal birth after cesarean (VBAC) deliveries in the United States, 1998-2002 birth cohorts.

To examine trends in repeat cesarean delivery, the characteristics of women who have repeat cesareans, and the risk of neonatal mortality for repeat cesarean birth compared to vaginal birth after cesarean (VBAC). Trends and characteristics of repeat cesareans were examined for: the period 1998-2002 for [1] all births, [2] low-risk births (singleton, term, vertex births) and [3] "no indicated risk" (NIR) births (singleton, term, vertex presentation births with no reported medical risks or complications). For low-risk and NIR births, neonatal mortality rates for repeat cesareans and VBACs were compared. Multivariate logistic regression was used to examine the risk of neonatal mortality for repeat cesareans and VBACs, after controlling for demographic and health factors. In 2002 the repeat cesarean rate was 87.4%, and varied little by maternal risk status or by demographic and health characteristics. From 1998-2002 rates increased by 20% for low risk and by 21% for NIR births, respectively. For low-risk women for the 1998-2002 birth cohorts, the adjusted odds ratio for neonatal mortality associated with repeat cesarean delivery (compared with VBAC) was 1.36 (95% C.I. 1.20-1.55). For NIR women, the adjusted odds ratio was 1.24 (0.99-1.55). The experience of a prior cesarean has apparently become a major indication for a repeat cesarean. Regardless of maternal risk status, almost 90% of women with a prior cesarean have a subsequent (i.e., repeat) cesarean delivery. This is the case even if there was no other reported medical indication. Our findings do not support the widely-held belief that neonatal mortality risk is significantly lower for repeat cesarean compared to VBAC delivery.

Expanded health data from the new birth certificate, 2006.

OBJECTIVES: This report presents 2006 data on new checkbox items exclusive to the 2003 U.S. Standard Certificate of Live Birth. Information is shown for checkboxes in the following categories: "risk factors in this pregnancy," "obstetric procedures," "characteristics of labor and delivery," "method of delivery," "abnormal conditions of the newborn," and "congenital anomalies of the newborn." These categories are included on both the 1989 and the 2003 U.S. Standard Certificates of Live Birth; however, many of the specific checkboxes were modified, or are new to the 2003 certificate. Data on selected new (not modified) checkboxes are presented in this report. METHODS: Descriptive statistics are presented on births occurring in 2006 to residents of the 19 states that had implemented the 2003 U.S. Standard Certificate of Live Birth as of January 1, 2006. RESULTS: There were 2,073,368 births to residents of the 19-state reporting area, representing 49 percent of 2006 U.S. births. The rate of prepregnancy diabetes was 6.8 per 1,000 births and gestational diabetes was 38.7; risk of both types of diabetes rose rapidly with advancing maternal age. Cervical cerclage was reported at a rate of 2.9 per 1,000. External cephalic version was used in 3.2 of every 1,000 births; its success rate decreased with increasing maternal age. Almost all attempts at forceps or vacuum delivery were successful. About 25 percent of women who had a cesarean delivery attempted a trial of labor. Fifteen percent of women received antibiotics during labor. Rates for antenatal steroids (8.4) and surfactant replacement therapy (3.2) decreased with increasing gestational age. Large differences by race and Hispanic origin were generally seen for the receipt of steroids and surfactant replacement therapy regardless of gestational age. Six percent of all infants were admitted to a neonatal intensive care unit (NICU).

Expanded health data from the new birth certificate, 2005.

OBJECTIVES: This report presents data for 2005 on checkbox items exclusive to the 2003 U.S. Standard Certificate of Live Birth. Information is shown for checkboxes in the following categories: Risk factors in this pregnancy, Obstetric procedures, Characteristics of labor and delivery, Method of delivery, Abnormal conditions of the newborn, and Congenital anomalies of the newborn. These categories are included on both the 1989 and the 2003 U.S. Standard Certificate of Live Birth; however, many of the specific checkbox items were modified, or are new to the 2003 certificate. Data on selected new checkbox items are presented in this report. METHODS: Descriptive tabulations are presented on births occurring in 2005 to residents of the 12 states (Florida, Idaho, Kansas, Kentucky, Nebraska, New Hampshire, New York (excluding New York City), Pennsylvania, South Carolina, Tennessee, Texas, and Washington), which implemented the 2003 U.S. Standard Certificate of Live Birth as of January 1, 2005. RESULTS: There were 1,268,502 births to residents of the 12-state area in 2005 (31 percent of all U.S. births). Gestational and prepregnancy diabetes were reported at rates of 39.3 and 6.9 per 1,000. Infants of women with diabetes, especially prepregnancy diabetes, were more likely to be high birthweight and to be admitted to a neonatal intensive care unit (NICU) than infants of women without diabetes. The rate of cervical cerclage was 3.7 per 1,000; this procedure was used more frequently in twin and higher order births than in singleton births. Almost all attempts at forceps or vacuum delivery (almost 99 percent) were successful. Almost one-third of all women who had a cesarean delivery had attempted a trial of labor. Antibiotics were given to 17 percent of women during labor. Steroids (glucocorticoids) for fetal lung maturation were received prior to delivery by 1 percent of all mothers. Surfactant replacement therapy was received by newborns at a rate of 3.7 per 1,000; rates were higher for infants delivered very preterm (less than 32 weeks of gestation). Large differences by race and Hispanic origin were seen for the receipt of steroids and for surfactant replacement therapy. More than 6 percent of all infants were admitted to a NICU. Nearly one-half of all singleton infants admitted to a NICU were delivered at term. Cyanotic congenital heart disease (56.9 per 100,000 infants) and hypospadias (126.2 per 100,000 male births only) were among the most frequently reported congenital anomalies.

Cesarean birth in the United States: epidemiology, trends, and outcomes.

The percentage of United States cesarean births increased from 20.7% in 1996 to 31.1% in 2006. Cesarean rates increased for women of all ages, race/ethnic groups, and gestational ages and in all states. Both primary and repeat cesareans have increased. Increases in primary cesareans in cases of "no indicated risk" have been more rapid than in the overall population and seem the result of changes in obstetric practice rather than changes in the medical risk profile or increases in "maternal request." Several studies note an increased risk for neonatal and maternal mortality for medically elective cesareans compared with vaginal births.

Neonatal mortality for primary cesarean and vaginal births to low-risk women: application of an "intention-to-treat" model.

BACKGROUND: The percentage of United States births delivered by cesarean section continues to increase, even for women considered to be at low risk for the procedure. The purpose of this study was to use an "intention-to-treat" methodology, as recommended by a National Institutes of Health conference, to examine neonatal mortality risk by method of delivery for low-risk women. METHODS: Low-risk births were singleton, term (37-41 weeks' gestation), vertex births, with no reported medical risk factors or placenta previa and with no prior cesarean section. All U.S. live births and infant deaths for the 1999 to 2002 birth cohorts (8,026,415 births and 17,412 infant deaths) were examined. Using the intention-to-treat methodology, a "planned vaginal delivery" category was formed by combining vaginal births and cesareans with labor complications or procedures since the original intention in both cases was presumably a vaginal delivery. This group was compared with cesareans with no labor complications or procedures, which is the closest approximation to a "planned cesarean delivery" category possible, given data limitations. Multivariable logistic regression was used to model neonatal mortality as a function of delivery method, adjusting for sociodemographic and medical risk factors. RESULTS: The unadjusted neonatal mortality rate for cesarean deliveries with no labor complications or procedures was 2.4 times that for planned vaginal deliveries. In the most conservative model, the adjusted odds ratio for neonatal mortality was 1.69 (95% CI 1.35-2.11) for cesareans with no labor complications or procedures, compared with planned vaginal deliveries. CONCLUSIONS: The finding that cesarean deliveries with no labor complications or procedures remained at a 69 percent higher risk of neonatal mortality than planned vaginal deliveries is important, given the rapid increase in the number of primary cesarean deliveries without a reported medical indication.

Expanded health data from the new birth certificate, 2004.

OBJECTIVES: This is the first report to present maternal and infant health information exclusive to the 2003 revision of the U.S. Standard Certificate of Live Birth. Information is shown for the items: Risk factors in this pregnancy, Obstetric procedures, Characteristics of labor and delivery, Method of delivery, Abnormal conditions of the newborn, and Congenital anomalies of the newborn. These items are included on both the 1989 and the 2003 U.S. Standard Certificate of Live Birth; however, many of the specific checkboxes were modified, or are new to the 2003 certificate. The new checkboxes are the focus of this report. METHODS: Descriptive tabulations are presented on births occurring in 2004 to residents of the seven states (Idaho, Kentucky, New York (excluding New York City), Pennsylvania, South Carolina, Tennessee, and Washington), which implemented the 2003 U.S. Standard Certificate of Live Birth as of January 1, 2004. RESULTS: There were 571,858 births to residents of the seven-state area in 2004 (14 percent of all U.S. births). Gestational and prepregnancy diabetes were reported at rates of 44.0 and 7.2 per 1,000; levels for both types of diabetes increased steadily with maternal age. One percent (1.4) of births were reported to have resulted from infertility therapies; nearly all (90 percent) of the infertility therapy-related births were to non-Hispanic white mothers. More than one-half of all attempts at external cephalic version successfully converted the infant to vertex position. Steroids for fetal lung maturation were administered prior to delivery to 13 of every 1,000 newborns and were inversely associated with gestational age. More than two-thirds of all women received epidurals to help control the pain of labor. A trial of labor was reportedly attempted for 36 percent of all women who then had a cesarean delivery. Six percent of singletons, one-third of all twins, and more than three-fourths of triplets were admitted to a neonatal intensive care unit (NICU) at delivery (Figure 1). The most frequently reported congenital anomalies were cyanotic heart disease (81 per 100,000 infants) and hypospadias (174 per 100,000 male births).

Births: final data for 2005.

OBJECTIVES: This report presents 2005 data on U.S. births according to a wide variety of characteristics. Data are presented for maternal demographic characteristics including age, live-birth order, race, Hispanic origin, marital status, and educational attainment; maternal lifestyle and health characteristics (medical risk factors, weight gain, and tobacco use); medical care utilization by pregnant women (prenatal care, obstetric procedures, characteristics of labor and/or delivery, attendant at birth, and method of delivery); and infant characteristics (period of gestation, birthweight, Apgar score, congenital anomalies, and multiple births). Also presented are birth and fertility rates by age, live-birth order, race, Hispanic origin, and marital status. Selected data by mother's state of residence are shown, as well as data on month and day of birth, sex ratio, and age of father. Trends in fertility patterns and maternal and infant characteristics are described and interpreted. METHODS: Descriptive tabulations of data reported on the birth certificates of the 4.1 million births that occurred in 2005 are presented. Denominators for population-based rates are postcensal estimates derived from the U.S. 2000 census. RESULTS: In 2005, 4,138,349 births were registered in the United States, 1 percent more than in 2004. The 2005 crude birth rate was 14.0, unchanged from the previous year; the general fertility rate increased slightly to 66.7. Teenage childbearing continued to decline, dropping to the lowest levels recorded. Rates for women aged 20-29 were fairly stable, whereas childbearing among women 30 years of age and older increased. All measures of unmarried childbearing rose substantially in 2005. Smoking during pregnancy continued to decline. No improvement was seen in the timely initiation of prenatal care. The cesarean delivery rate climbed to more than 30 percent of all births, another all-time high. Preterm and low birthweight rates also continued to rise; the twin birth rate was unchanged and the rate of triplet and higher order multiple births declined for the 7th consecutive year.

Births: final data for 2004.

OBJECTIVES: This report presents 2004 data on U.S. births according to a wide variety of characteristics. Data are presented for maternal demographic characteristics including age, live-birth order, race, Hispanic origin, marital status, and educational attainment; maternal lifestyle and health characteristics (medical risk factors, weight gain, and tobacco use); medical care utilization by pregnant women (prenatal care, obstetric procedures, characteristics of labor and/or delivery, attendant at birth, and method of delivery); and infant characteristics (period of gestation, birthweight, Apgar score, congenital anomalies, and multiple births). Also presented are birth and fertility rates by age, live-birth order, race, Hispanic origin, and marital status. Selected data by mother's state of residence are shown, as well as data on month and day of birth, sex ratio, and age of father. Trends in fertility patterns and maternal and infant characteristics are described and interpreted. METHODS: Descriptive tabulations of data reported on the birth certificates of the 4.1 million births that occurred in 2004 are presented. Denominators for population-based rates are post-censal estimates derived from the U.S. 2000 census. RESULTS: In 2004, 4,112,052 births were registered in the United States, less than 1 percent more than the number in 2003. The crude birth rate declined slightly; the general fertility rate increased by less than 1 percent. Childbearing among teenagers and women aged 20-24 years declined to record lows. Rates for women aged 25-34 and 45-49 years were unchanged, whereas rates for women aged 35-44 years increased. All measures of unmarried childbearing rose in 2004. Smoking during pregnancy continued to decline. No improvement was seen in the timely initiation of prenatal care. The cesarean delivery rate jumped 6 percent to another all-time high, whereas the rate of vaginal birth after previous cesarean fell by 13 percent. Preterm and low birthweight rates continued their steady rise. The twinning rate increased, but the rate of triplet and higher order multiple births was down slightly.

Cesarean delivery: background, trends, and epidemiology.

OBJECTIVE: To examine trends in cesarean delivery for the overall population and for women with "no indicated risk" for cesarean section, and to summarize the available literature on "maternal request" cesarean deliveries. FINDINGS: Nearly 3 in 10 births were delivered by cesarean section in 2004 (29.1%), the highest rate ever reported in the United States. The overall rate has increased by over 40% since 1996, reflecting two concurrent trends: an increase in the primary rate (14.6% to 20.6%), and a steep decline in the rate of vaginal birth after cesarean (28.3% to 9.2%). There has been a clear increase in primary cesarean delivery without a medical or obstetrical indication, and studies using hospital discharge data or birth certificate data estimate the rate of primary cesarean deliveries with no reported medical or obstetrical indication to be between 3% and 7% of all deliveries to women who had not had a previous cesarean delivery. However, these studies contain no direct information on whether these cesareans were the result of maternal request or because of physician recommendation. There was little data to support the contention that the rise in the cesarean rate was the result of maternal request. CONCLUSION: There are no systematic data available on cesarean delivery by "maternal request." However, the rate of primary cesarean delivery is increasing rapidly for women of all ages, races, and medical conditions, as well as for births at all gestational ages. Since a first cesarean section virtually guarantees that subsequent pregnancies will be cesarean deliveries (the repeat cesarean delivery rate is now almost 91%), research is needed on physician practice patterns, maternal attitudes, clinical outcomes for mother and infant (harms, benefits), and clinical and nonclinical factors (institutional, legal, economic) that affect the decision to have a cesarean delivery.

Infant and neonatal mortality for primary cesarean and vaginal births to women with "no indicated risk," United States, 1998-2001 birth cohorts.

BACKGROUND: The percentage of United States' births delivered by cesarean section has increased rapidly in recent years, even for women considered to be at low risk for a cesarean section. The purpose of this paper is to examine infant and neonatal mortality risks associated with primary cesarean section compared with vaginal delivery for singleton full-term (37-41 weeks' gestation) women with no indicated medical risks or complications. METHODS: National linked birth and infant death data for the 1998-2001 birth cohorts (5,762,037 live births and 11,897 infant deaths) were analyzed to assess the risk of infant and neonatal mortality for women with no indicated risk by method of delivery and cause of death. Multivariable logistic regression was used to model neonatal survival probabilities as a function of delivery method, and sociodemographic and medical risk factors. RESULTS: Neonatal mortality rates were higher among infants delivered by cesarean section (1.77 per 1,000 live births) than for those delivered vaginally (0.62). The magnitude of this difference was reduced only moderately on statistical adjustment for demographic and medical factors, and when deaths due to congenital malformations and events with Apgar scores less than 4 were excluded. The cesarean/vaginal mortality differential was widespread, and not confined to a few causes of death. CONCLUSIONS: Understanding the causes of these differentials is important, given the rapid growth in the number of primary cesareans without a reported medical indication.

Maternal risk profiles and the primary cesarean rate in the United States, 1991-2002.

OBJECTIVES: We examined factors contributing to shifts in primary cesarean rates in the United States between 1991 and 2002. METHODS: US national birth certificate data were used to assess changes in primary cesarean rates stratified according to maternal age, parity, and race/ethnicity. Trends in the occurrence of medical risk factors or complications of labor or delivery listed on birth certificates and the corresponding primary cesarean rates for such conditions were examined. RESULTS: More than half (53%) of the recent increase in overall cesarean rates resulted from rising primary cesarean rates. There was a steady decrease in the primary cesarean rate from 1991 to 1996, followed by a rapid increase from 1996 to 2002. In 2002, more than one fourth of first-time mothers delivered their infants via cesarean. Changing primary cesarean rates were not related to general shifts in mothers' medical risk profiles. However, rates for virtually every condition listed on birth certificates shifted in the same pattern as with the overall rates. CONCLUSIONS: Our results showed that shifts in primary cesarean rates during the study period were not related to shifts in maternal risk profiles.

Annual summary of vital statistics: 2004.

The crude birth rate in 2004 was 14.0 births per 1000 population, the second lowest ever reported for the United States. The number of births and the fertility rate (66.3) increased slightly (by <1%) from 2003 to 2004. Fertility rates were highest for Hispanic women (97.7), followed by Asian or Pacific Islander (67.2), non-Hispanic black (66.7), Native American (58.9), and non-Hispanic white (58.5) women. The birth rate for teen mothers continued to fall, dropping 1% from 2003 to 2004 to 41.2 births per 1000 women aged 15 to 19 years, which is another record low. The teen birth rate has fallen 33% since 1991; declines were more rapid for younger teens aged 15 to 17 (43%) than for older teens aged 18 to 19 (26%). The proportion of all births to unmarried women is now slightly higher than one third. Smoking during pregnancy declined slightly from 2003 to 2004. In 2004, 29.1% of births were delivered by cesarean delivery, up 6% since 2003 and 41% since 1996 (20.7%). The primary cesarean delivery rate has risen 41% since 1996, whereas the rate of vaginal birth after a previous cesarean delivery has fallen 67%. The use of timely prenatal care was 84.0% in both 2003 and 2004. The percentage of preterm births rose to 12.5% in 2004 from 10.6% in 1990 and 9.4% in 1981. The percentage of low birth weight births also increased to 8.1% in 2004, up from 6.7% in 1984. Twin birth rate and triplet/+ birth rates increased by 1% and <1%, respectively, from 2002 to 2003. Multiple births accounted for 3.3% of all births in 2003. The infant mortality rate was 7.0 per 1000 live births in 2002 compared with 6.8 in 2001. The ratio of the infant mortality rate among non-Hispanic black infants to that for non-Hispanic white infants was 2.4 in 2002, the same as in 2001. The United States continues to rank poorly in international comparisons of infant mortality. Expectation of life at birth reached a record high of 77.6 years for all gender and race groups combined. Death rates in the United States continue to decline, with death rates decreasing for 8 of the 15 leading causes. Death rates for children < or =19 years of age declined for 7 of the 10 leading causes in 2003. The death rates did not increase for any cause, and rates for heart disease, influenza, and pneumonia and septicemia did not change significantly for children as a group. A large proportion of childhood deaths, however, continue to occur as a result of preventable injuries.

Method of delivery and neonatal mortality among very low birth weight infants in the United States.

OBJECTIVE: To examine the association between method of delivery (primary cesarean section vs. vaginal) and neonatal mortality risk (as well as causes of death) among very low-birth weight first-born infants in the United States. More specifically, to examine this association separately for breech/malpresenting and vertex-presenting infants, while adjusting for selected maternal characteristics, and pregnancy, labor and delivery complications. METHODS: The study population was derived from the 1995-1998 birth cohort linked birth/infant death data sets. Binary and multinomial logit regression analyses were performed to assess the relationship in four very low-birth weight categories. RESULTS: Among breech/malpresenting neonates, compared to those delivered vaginally, infants delivered by a primary cesarean section had significantly lower adjusted relative risks of death for all very low-birth weight categories and the decrease in relative risk tended to be larger with each increasing birth weight category. However, for vertex-presenting neonates, results are mixed, suggesting decreased relative mortality risks associated with primary cesarean section, which were significant for 500-749 g, not significant for 750-999 g, and barely significant for 1,000-1,249 g. In contrast, for vertex-presenting neonates weighing 1,250-1,499 g, there was a significantly increased adjusted relative risk associated with primary cesarean section. Differences in cause-specific neonatal mortality by method of delivery and presentation status were also discussed. CONCLUSIONS: Primary cesarean section appears to be associated with decreased neonatal mortality risks in each very low-birth weight category for breech/malpresenting infants, but results are mixed for vertex-presenting infants. Causal inferences should be avoided because this was an observational study by design.