Objective
The purpose of this study was to evaluate the impact of group prenatal care on rates of preterm birth.
Study Design
We conducted a retrospective cohort study of 316 women in group prenatal care that was compared with 3767 women in traditional prenatal care. Women self-selected participation in group care.
Results
Risk factors for preterm birth were similar for group prenatal care vs traditional prenatal care: smoking (16.9% vs 20%; P = .17), sexually transmitted diseases (15.8% vs 13.7%; P = .29), and previous preterm birth (3.2% vs 5.4%; P = .08). Preterm delivery (<37 weeks’ gestation) was lower in group care than traditional care (7.9% vs 12.7%; P = .01), as was delivery at <32 weeks’ gestation (1.3% vs 3.1%; P = .03). Adjusted odds ratio for preterm birth for participants in group care was 0.53 (95% confidence interval, 0.34–0.81). The racial disparity in preterm birth for black women, relative to white and Hispanic women, was diminished for the women in group care.
Conclusion
Among low-risk women, participation in group care improves the rate of preterm birth compared with traditional care, especially among black women. Randomized studies are needed to eliminate selection bias.
Preterm birth is a serious, international public health issue. In the short term, preterm infants require more medical treatment than full-term infants; the treatment ranges from antibiotics and phototherapy to mechanical ventilation and total parenteral nutrition. Other complications of prematurity, such as cerebral palsy and retinopathy, can lead to life-long handicap. The annual cost of treatment for these and other complications that arise from preterm birth has been estimated at >26 billion dollars in the United States alone.
For Editors’ Commentary, see Contents
Risk factors for spontaneous preterm delivery are well described and include a history of previous preterm birth, multiple gestation, vaginal bleeding, low prepregnancy weight, systemic and genital tract infection, maternal smoking, and non-white race among others. Although prescription of 17 alpha-hydroxyprogesterone caproate has led to reductions in the rates of recurrent preterm delivery, there is no similarly effective means of primary prevention for women who are otherwise at low risk for preterm birth. Instead, clinicians focus on symptom-based screening and physical examination, and treatment is aimed at arresting the labor process after it has begun.
South Carolina has one of the highest rates of preterm birth in the country; 14.3% of women deliver at <37 weeks’ gestation. There is also a tremendous racial/ethnic disparity in rates of prematurity; 19.7% of non-Hispanic black women deliver preterm compared with 12.7% of non-Hispanic white women and 13.0% of Hispanic women. The Greenville Hospital System Obstetrics Center, located in Greenville, SC, provides prenatal care primarily to medically underserved women. Given the vulnerability of the population that is served, historic rates of premature birth among women in this practice (16.4%) are markedly higher than both state and national averages.
In an effort to address this long-standing issue, the Greenville Hospital System Obstetrics Center began to offer CenteringPregnancy group prenatal care in March 2009. CenteringPregnancy is a national model of group prenatal care that has shown promise in reducing the rates of preterm birth. The originators drew on basic adult learning theories that highlight the importance of group work and participatory processes to develop the model, although no single theory of health behavior was central to their design.
The Centering Healthcare Institute (Boston, MA) maintains the curriculum and evaluates and approves sites that offer this trademarked model of group prenatal care. Participation typically is limited to low-risk women and excludes women with preexisting medical conditions or high-risk pregnancies, such as multiple gestations. Groups of up to 8-12 pregnant women at approximately the same gestational age are brought together 10 times over 6 months. Physical assessment by a credentialed medical care provider occurs within the group space, and women actively participate in their own medical care by taking responsibility for measuring their weight and blood pressure. Each 2-hour session follows an educational curriculum that includes information about health and nutrition, childbirth preparation, stress reduction, relationships, and parenting. Facilitated group discussion encourages active participation. There is an emphasis on relationship building that can result in improved social support for the group members. In most settings, groups are led by certified nurse-midwives or nurse-practitioners.
To date, only one large randomized controlled trial that evaluated pregnancy outcomes for women who were enrolled in group prenatal care has been conducted. The authors found that the rate of preterm birth among women in group care was 33% lower than the rate of preterm birth for women in the traditional prenatal care control group (9.8% vs 14.8%). The subsample of black women demonstrated a 41% difference in the rate of preterm delivery (10.1% in group care vs 15.9% in traditional care). Reductions in the rates of prematurity and low birthweight have been inconsistent in smaller matched cohort studies.
The purpose of this study was to conduct a retrospective cohort study to determine the impact of the CenteringPregnancy model of group prenatal care on rates of preterm birth for women who are enrolled in group care compared with women who receive care in traditional prenatal care. This study will contribute the literature by examining the effectiveness of this evidence-based model outside of a highly structured clinical trial setting, with a large enough sample to document any observed changes in birth outcomes.
Methods
During the implementation of group prenatal care in our practice, we developed guidelines that limited eligibility for group participation to low-risk patients and that was consistent with both the scope of practice of the nurse-practitioners and nurse-midwives who were providing care in the groups and the CenteringPregnancy model design. Exclusion criteria for participation in group care included, but were not limited to, pregestational diabetes mellitus, chronic hypertension, multiple gestation, obesity (defined by body mass index >45 kg/m 2 ), severe psychiatric disease, untreated drug or alcohol addiction, and other medical complications of pregnancy that require higher levels of surveillance, such as HIV infection and maternal cardiac or renal disease. Beginning in March 2009, all women with low-risk pregnancies seeking prenatal care in the first trimester were given the option of receiving care in the group prenatal care model. Patients were recruited for groups at the time of their first prenatal care visit by either a nurse-practitioner or a nurse-midwife, and the final determination regarding eligibility was made by the provider.
All groups were conducted according to the trademarked CenteringPregnancy curriculum, which has been described in previous publications. Participation in group care was not randomized, but rather left to the discretion of the individual patient. Patients in group care had the option of accessing additional visits in a traditional individual care setting as needed if health problems arose.
Typical monthly enrollment in group care ranged between 30–45 patients. A log of all participants was maintained to track the outcomes of these patients for ongoing quality control. Participation was defined as attendance at even 1 group session, and the total number of groups attended was recorded for each participant. Women were permitted to withdraw from group care and continue with traditional care if desired; this was also recorded for each participant. Medical care in groups was provided by nurse-midwives and nurse-practitioners. After the first 8 months of implementation, many groups also included a medical student, a resident physician in obstetrics and gynecology, or a resident physician in family medicine.
In December 2010, institutional review board approval was granted by the Greenville Hospital System University Medical Center for a retrospective cohort study to evaluate program outcomes. Demographic information and pregnancy outcomes were obtained from the electronic birth certificate database that is maintained by the hospital. Preterm birth was considered as any delivery at <37 weeks’ gestational age by the best obstetric estimate of gestational age at delivery, which was collected in accordance with the Centers for Disease Control and Prevention’s National Center for Health Statistics Handbook and the 2003 revision of the US Standard Certificate of Live Birth.
Adequacy of prenatal care was determined with standard scoring on the Kotelchuck Adequacy of Prenatal Care Utilization index, which is also included in the 2003 revision of the US Standard Certificate of Live Birth. This index is based on the American College of Obstetricians and Gynecologists prenatal care standards for uncomplicated pregnancies and characterizes care into 1 of 4 categories according to the timing of initiation of care, the total number of prenatal care visits received, and the gestational age at delivery. Women are categorized as receiving “inadequate” care if they enter prenatal care after the month 4 of pregnancy (16 weeks’ gestational age) or receive <50% of the expected visits. All other categories require entry to care in months 1-4. The “intermediate” category requires attendance at 50-79% of the expected visits; the “adequate” category requires attendance at 80-109% of the expected visits; and the “adequate +” category requires attendance at >110% of the expected visits.
The study cohort consisted of women who delivered live-born singleton infants between March 2009 and December 2010, who received Medicaid coverage at the time of delivery, who entered prenatal care within the first 16 weeks of pregnancy, and who had no pregestational diabetes mellitus or hypertension. If women had >1 birth during the study period, only the first delivery was included to maintain independence.
Bivariate group comparisons between women who received group care and those in the control group who received traditional care were made with the use of χ 2 analysis for categoric data and the Student t test for continuous data. Multiple logistic regression analysis was used to obtain adjusted odds ratios for preterm birth for patients who were enrolled in group care vs the control group of women who participated in traditional prenatal care; adjustment was made for known risk factors and group differences. Significance level was set at the probability level of .05. All statistical analyses were performed with SAS statistical software (version 9.2; SAS Institute Inc, Cary, NC).
Results
During the study period, there were 9630 singleton live-born deliveries at Greenville Memorial Hospital; 339 of these women participated in group prenatal care. After exclusions, the final study population consisted of 4083 women: 316 women in group care and 3767 women in traditional care ( Figure ). Women in the group care cohort attended a median of 7 (interquartile range, 5–8) sessions of the 10 scheduled group sessions. Forty-eight women (15%) withdrew from the group care program after a median of 1 (range, 1–5) sessions, but their pregnancy outcomes were evaluated with the group care cohort in an intent-to-treat analysis.
Maternal demographic characteristics were significantly different between groups ( Table 1 ). Women who enrolled in group prenatal care were younger, more likely to be a minority, and nulliparous, and to have entered prenatal care earlier in comparison with women in traditional care. Risk factors for preterm birth such as the presence of sexually transmitted infections, tobacco use during pregnancy, and history of previous preterm birth were similar for both groups.
| Entire cohort | |||
|---|---|---|---|
| Characteristic | Group care (n = 316) | Traditional care (n = 3767) | P value a |
| Maternal age, y b | 23.1 ± 4.6 | 25.1 ± 5.6 | < .001 |
| Maternal race/ethnicity, n (%) | < .001 | ||
| White | 107 (33.9) | 1725 (45.8) | |
| Black | 107 (33.9) | 961 (25.5) | |
| Hispanic | 55 (17.4) | 835 (22.2) | |
| Other | 47 (14.9) | 246 (6.5) | |
| Marital status, n (%) | < .001 | ||
| Married | 75 (23.7) | 1314 (34.9) | |
| Unmarried, Father not named | 99 (31.3) | 1000 (26.6) | |
| Unmarried, Father named | 141 (44.6) | 1433 (38.0) | |
| Unknown | 1 (0.3) | 20 (0.5) | |
| Education, n (%) | .266 | ||
| <High school | 114 (36.1) | 1532 (40.7) | |
| High school diploma/GED | 105 (33.2) | 1176 (31.3) | |
| >High school | 97 (30.7) | 1055 (28.0) | |
| Month prenatal care began, n (%) | < .001 | ||
| 0-2 mo | 181 (57.3) | 1288 (34.2) | |
| 3-4 mo | 135 (42.7) | 2479 (65.8) | |
| Kotelchuck Index, n (%) | < .001 | ||
| Inadequate | 16 (5.1) | 182 (4.8) | |
| Intermediate | 17 (5.4) | 380 (10.1) | |
| Adequate | 114 (36.1) | 1786 (47.4) | |
| Adequate + | 169 (53.5) | 1419 (37.7) | |
| Tobacco use during pregnancy, n (%) | .166 | ||
| No | 263 (83.2) | 3012 (80.0) | |
| Yes | 53 (16.8) | 753 (20.0) | |
| Sexually transmitted disease infection, n (%) c | .287 | ||
| No | 266 (84.2) | 3252 (86.3) | |
| Yes | 50 (15.8) | 515 (13.7) | |
| Parity, n (%) | < .001 | ||
| 0 | 199 (63.0) | 1549 (41.1) | |
| ≥1 | 117 (37.0) | 2218 (58.9) | |
| Previous preterm birth, n (%) | .082 | ||
| No | 306 (96.8) | 3562 (94.6) | |
| Yes | 10 (3.2) | 205 (5.4) | |
a Maternal age comparison was made with t test; the comparison of the remainder was made with χ 2 ;
b Data are given as mean ± SD;
c Nesseria gonorrhea, Chlamydia tracho matis, Herpes simplex.
The mean gestational age at delivery was 38.8 ± 2.2 (SD) weeks for women in group prenatal care, which was greater than for women in traditional care who demonstrated a mean gestational age at delivery of 38.3 ± 2.7 weeks ( P < .001). Similarly, mean birthweight was 3245 ± 579 g for women in group care compared with 3178 ± 654 g for women in traditional care ( P = .05). Previous preterm birth, maternal race, marital status, and adequacy of prenatal care were associated with preterm delivery at <37 weeks’ gestation ( P < .001 for all). Bivariate comparisons of birth outcomes for all women in group care compared with all women in traditional care are available in Table 2 .
| Entire cohort, n (%) | |||
|---|---|---|---|
| Characteristic | Group care (n = 316) | Traditional care (n = 3767) | P value a |
| Gestational age at delivery, wk | .034 | ||
| <32 | 4 (1.3) | 118 (3.1) | |
| 32-36 | 21 (6.7) | 359 (9.5) | |
| ≥37 | 291 (92.1) | 3290 (87.3) | |
| Birthweight, g | .265 | ||
| <1500 | 5 (1.6) | 112 (3.0) | |
| 1500-2400 | 23 (7.3) | 318 (8.4) | |
| ≥2500 | 288 (91.1) | 3337 (88.6) | |
| Admission to neonatal intensive care unit | .082 | ||
| No | 294 (93.0) | 3391 (90.0) | |
| Yes | 22 (7.0) | 376 (10.0) | |
| Breastfed | .099 | ||
| No | 111 (35.1) | 1501 (39.9) | |
| Yes | 205 (64.9) | 2266 (60.1) | |
The rate of preterm delivery at <37 weeks’ gestation was 7.9% for women in group care and 12.7% for women in traditional care ( P = .01). Rates of preterm delivery at <32 weeks’ gestation were also lower, with a rate of 1.3% for women in group care and 3.1% for women in traditional care ( P = .03). There was no difference in rates of low infant birthweight <2500 g (8.9% group care vs 11.4% traditional care; P = .20) or neonatal intensive care unit admission (7.0% group care vs 10.0% traditional care; P = .08). Multivariate regression analysis that included maternal age, race, marital status, nulliparity, early entry to prenatal care, adequacy of prenatal care, and history of previous preterm delivery demonstrated that participation in group prenatal care was highly protective for preterm delivery (odds ratio [OR], 0.53; 95% confidence interval [CI], 0.34–0.81; Table 3 ).
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