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. 2016 Mar 18;2:182–193. doi: 10.1016/j.ssmph.2016.01.007

Table 3.

Study characteristics.

Author, Setting Study design Participant characteristics Relevant outcomesa Quality rating, comments
Benator et al.(2013) Matched, retrospective cohort Midwifery group (n=872); primarily low income, 21.9%<19 years old, 85% African American, African American subgroup (n=744)
  • –

    PTBb 7.9% vs. 11.0% (OR=0.70, p<0.01)

  • –

    AA sub-analysis 8.6% vs. 11.8% (OR=0.71, p<0.01)

  • –

    5 min Apgar <7, 3.4% vs. 3.7% (OR=0.92, nssd)

  • –

    AA sub-analysis 3.4% vs. 3.7% (OR=0.90, nssd)

  • –

    LBWc 8.0% vs. 10.0% (OR=0.81, nssd)

  • –

    AA sub-analysis 9.8% vs. 11.1% (OR=0.872, nssd)

  • –

    Average birth weight at term 3325 g vs. 3282 g (p<0.01)

  • –

    AA sub-analysis 3325 g vs. 3282 g (p<0.01)

 Moderate quality
Washington DC, USA 2005-2008 Intent to treat analysis
Birth certificate data
Clients initiating prenatal care from nurse-midwives at a free-standing birth center vs. women receiving usual care Propensity scoring used to construct a matched comparison group
Usual care group (n=42 987); derived from propensity scoring, matched to the study population on sociodemographic, medical, and health history characteristics; AA subgroup (n=27 095)
No reported distinction between primary and secondary outcomes
Included:
  • –

    women who gave birth in DC, and DC residents who gave birth in other jurisdictions

  • –

    at least 2 prenatal visits

  • –

    singleton birth

  • –

    gestational age > 24 weeks

Simonet et al.(2009) Retrospective cohort Hudson Bay Inuit births (n=1529); 36.0% primiparous, 39.1% single mothers, 61.5%<11 yrs. education
  • –

    PTBd 10.3% vs. 10.8% (OR=0.94, 95% CI: 0.73, 1.20)

  • –

    SGAe 6.1% vs. 5.4% (OR=1.48, 95% CI: 0.82, 2.68

  • –

    LBWc 5.3% vs. 6.0% (OR=0.85, 95% CI: 0.61, 1.18)

 Moderate quality
14 Inuit communities of Hudson Bay and Ungava Bay, Nunavik, QC, Canada 1989-2000 Statistics Canada׳s linked live birth, infant death, and stillbirth data Adjustment for age, educ., marital status, parity, infant, sex, plurality, community size and community-level random effects
No adjustment for preexisting health complications or maternal morbidity
Authors acknowledged failure to reach 80% power (a=0.05) for a 30% difference in the primary outcome
Ungava Bay Inuit births (n=1197); 29.7% primiparous, 43.1% single mothers, 64.6%<11 yrs. education
Midwives provided majority of prenatal care and attended over 73% of deliveries in Hudson Bay vs. physicians who provided prenatal care and attended 95% of deliveries in Ungava Bay
Included:
  • –

    women residing in Nunavik, based on geocoding maternal residence

    Excluded:

  • –

    births with missing data on birthweight or gestational age

  • –

    births < 500 g or < 20 wks. gestation

  • –

    women with non-Inuit mother tongue

Primary outcome: perinatal death, relevant secondary outcomes: PTB, SGA, LBW
Jackson et al.(2003) Prospective cohort study/ retrospective chart review Collaborative care (n=1808); 22%<20 yrs. old, 54% single mothers, 86% Hispanic
  • –

    5 min Apgar <7 0.8% vs. 0.4% (RD=0.9, 95% CI: −3.7, 5.4)

  • –

    PTBd 6.4% vs. 6.5% (RD=0.2, 95% CI: −1.7, 2.1)

  • –

    LBWc 3.8% vs. 4.0% (RD=0.5, 95% CI: −1.7, 2.7)

  • –

    VLBWf 0.5% vs. 0.6% (RD=−0.2, 95% CI: −5.6, 5.2)

  • –

    SGAe5.9% vs. 4.5% (RD=1.7, 95% CI: −1.5, 4.8)

  • –

    NICU (any) 9.7% vs. 11.8% (RD=−1.3, 95% CI: −3.8, 1.1)

  • –

    NICU 1–3 days 3.3% vs. 5.6% (RD=−1.8, 95% CI: −3.9, 0.2)

 Moderate quality
Intent to treat analysis
Medical records and a self-administered patient survey OB-led traditional care (n=1149); 22%<20 yrs. old, 57% single mothers, 61% Hispanic
Adjusted for race/ethnicity, parity and caesarean section history, educ., age, marital status, country of origin, height, smoking during pregnancy
Crossover between study groups, 1.9% for collaborative care vs. 1.3% for traditional care
Power of 80% (a=.05) to detect significant risk differences of 3% to 5% for primary outcomes
Collaborative care offered at a birth center vs. OB/OB resident care Excluded:
  • –

    if ineligible for midwifery care at a birth center due to perinatal risk

  • –

    women with private or military insurance

  • –

    if entered care >33 wks. gestation
For collaborative care, 95% of the prenatal care was delivered by CNMs (65% of participants collaboratively managed through consultation or necessary visits with an OB), 5% by OBs
Collaborative care included case management, health education, nutrition counselling, social services
Primary outcomes: cesarean section; major antepartum, major intrapartum, or neonatal complications; NICU admissions
San Diego CA, USA Feb. 1, 1994-Nov. 1, 1996
Cragin, L.(2002) Retrospective cohort Nurse-midwifery care (n=801); 62% single mothers,>90% non-White, average educ. 9.6 yrs., 99% receiving Medicaid
  • –

    LBWc 5.5% vs. 6.7% nssd

 Moderate quality
Paper/computerized medical records Provider type determined by clinician with whom a patient had >60% of their care
Outcomes for nurse midwifery patients vs. OB patients at 2 study sites
OB-led care (n=372); 55% single mothers, >85% non-White, average educ. 11 yrs., 71% receiving Medicaid
“Modified intent to treat analysis”, ITT used except for women who transferred between provider types and received >60% of care from the second provider (n=21)
Adjustment made for maternal demographics and medical complications
Power estimated at 80% (a=0.05) to detect ß-371 for the primary outcome
Author acknowledged sample size was too small to find a statistically significant difference
Primary outcome: LBW, no relevant secondary outcomes
Inclusion:
  • –

    delivery at 1 of 2 study sites

  • –

    moderate medical or medical/social risk

  • –

    >60% of antenatal care with initial provider

    Excluded:

  • –

    women transferring care provider after 20 wks. gestation and having less than 75% of care at a study site

CA, USA April 1, 1999–March 31, 2000
Visintainer et al.(2000) Retrospective cohort study Enhanced care births (n=1474); 37% of women initiated care during the first trimester, 13% teen mothers
  • –

    LBWc (unadjusted) 4.1% vs. 6.9% (RR=0.59, 95% CI: 0.46, 0.73)

  • –

    Medicaid sub-analysis (RR=0.44, 95% CI: 0.34, 0.57)

  • –

    VLBWf (unadjusted) 0.6% vs. 1.4% (RR=0.44, 95% CI: 0.23, 0.85)

  • –

    Medicaid sub-analysis (RR=0.32, 95% CI: 0.16, 0.63)

 Moderate quality
Outcomes of enhanced care, which included prenatal care administered by nurse-midwives, vs. all County births Intent to treat analysis
County births (n=39 749); 77% of women initiated care during the first trimester, 5% teen mothers
Westchester County, NY, USA 1992-1994 Results stratified by 5 year age groups, race and Medicaid
Sub-analysis compared enhanced care cohort with country Medicaid births only Inclusion:
  • –

    recipient of Medicaid or no healthcare coverage (enhanced care clients only)

  • –

    resident of Westchester County

  • –

    15–44 years of age

  • –

    live birth >23 wks. gestation
No adjustment for preexisting health complications or perinatal risk
Enhanced care included: access to counselling, individual and group instruction on childbirth, nutrition and exercise, and a Medicaid worker to assist in enrollment in federal assistance programs
89% of a sample of women who began the enhanced care program delivered through it
Primary outcome: LBW
Blanchette(1995) Retrospective cohort CNM patients (n=496); 15.5%<19 yrs. old, 19.6% White, 19.2% initiated prenatal care < 12 wks., 10.3% substance abuse
  • –

    PTBg2.4% vs. 2.9%, nssd

  • –

    Apgar score 1 min. average 8.0 vs. 7.9, 7 min average 9.0 vs. 8.9, 1 min <7, 8.0% vs. 9.7%, 5 min<7, 0.8% vs. 1.1%, all nssd

  • –

    Birth weight <5 lbs 2.4% vs. 3.1%, nssd, all other birth weight comparisons nssd

 Weak quality
Berkeley, CA Clinic medical records No adjustment for confounders
Significantly different comparison groups
Compared outcomes for patients of a primary Care Access Clinic, the Clinic offered comprehensive care to all patients, with primary care delivered by CNMs who were supervised by 4 OBs vs. the OBs private practice patients OB patients (n=611); 2.6%<19 yrs. old, 62.4% White, 58.8% initiated prenatal care < 12 wks., substance use unknown
Patients transferring antepartum or intrapartum from midwifery to physician care (n=12) were excluded from the analysis
Included:
  • –

    any patients who accessed the CNMs at the Clinic or were private patients of the OBs during the study period

Excluded: CNM patients who transferred care antepartum/intrapartum due to medical risk
No reported distinction between primary and secondary outcomes
Fischler et al.(1995) Retrospective cohort CNM patients in private practice (n=111); 100% receiving Medicaid, 25%<12 yrs educ., 33% primiparous, 33% smokers
  • –

    Average birth weight positively associated with CNMs in private practice (3598 g) compared to MDs (3407.3 g, ß 0.13, p<0.05)

  • –

    nssd between average birth weight for CNM clients in a hospital clinic (3400.0 g) and MDs

  • –

    Low Apgar score, NICU admission, PTBh, and LBWh nssd between all comparison groups

 Moderate quality
A rural county in northwestern USA Jan. 1, 1989–June 30, 1990 Medical charts Adjustment for age, race, marital status, parity, educ., medical factors of pregnancy, smoking, adequacy of prenatal care, and setting
Compared outcomes for CNM patients in private practice to CNM patients in a hospital sponsored clinic, and to MD patients in a private practice setting CNM patients in a hospital-sponsored clinic (n=309); 17% receiving Medicaid, 32%<12 yrs. educ., 48% primiparous, 32% smokers
MD patients in private practice (n=297); 100% Medicaid, 51%<12 yrs. educ., 39% primiparous, 47% smokers No mention of how analysis was conducted for clients requiring transfer of care from CNMs to MDs/OBs for medical indication
No reported distinction between primary and secondary outcomes
Included:
  • –

    women identified as low-income either by Medicaid eligibility or financial screening by the County Health Dept.

    Excluded:

  • –

    women who attended a prenatal practice that used a combination of

  • –

    CNMs and MDs

  • –

    if prenatal care provider could not be identified

  • –

    multiple births

McLaughlin et al.(1992) RCT Comprehensive care (n=217); complete perinatal data (n=170), birth weight and demographic data only (n=183)
  • –

    LBWi 10% vs. 9%, nssd

  • –

    Average birthweight positively associated with comprehensive care for primiparas 3233 g vs. 3089 g (ß 0.17, p<0.05)

  • –

    nssd for all women and for multiparas

 Moderate quality
Davidson County, TN, USA Comprehensive care from a multi-disciplinary team including primary care from nurse-midwives vs. standard care from OB residents Intent to treat analysis
Sub-analysis of primiparas (n=86), sub-analysis of multiparas (n=97)
Subject loss for comprehensive group (n=34), for standard care group (n=44)
Standard care (n=211); complete perinatal data (n=138), birth weight and demographic data only (n=167)
Comprehensive care included care from social workers, a nutritionist, paraprofessional home visitors, and a psychologist
Sub-analysis of primiparas (n=79), sub-analysis of multiparas (n=88) Adjustment for age, African American race, marital status, educ., pregravid weight, male sex of infant, maternal height, pregravid medical problems, drug/alcohol use and smoking
Inclusion:
  • –

    women who attended Metropolitan Nashville General Hospital for their 1rst prenatal visit

  • –

    at risk for child maltreatment

  • –

    care initiated at <28 wks. gestation

  • –

    residing in Davidson County

  • –

    live-born singleton

Primary outcome: infant birth weight
Heins et al.(1990) RCT Clients randomized to nurse-midwifery care (n=728); <grade 12 63.1%, 10-19 risk score 73.5%, smoking >11 cig./day 38.0%
  • –

    PTB<37 and <33 wks. gestation 5% vs. 5%, nssd

  • –

    LBWc 15.4% vs. 16.3% (OR=0.92, 95% CI: 0.7, 1.2)

  • –

    AA sub-analysis 17.0% vs. 18% (OR=0.74, 95% CI: 0.5, 1.1)

  • –

    VLBWf 3.6% vs. 4.1% (OR=0.87, 95% CI: 0.5-1.5)

  • –

    AA sub-analysis 2.6% vs. 6.7% (OR=0.35, 95% CI: 0.1, 0.9)

 Moderate quality
South Carolina, USA July 1, 1983-Oct. 31, 1987 Comprehensive prenatal care provided primarily by nurse-midwives and nurses under their supervision vs. standard high risk prenatal care provided by OBs Intent to treat analysis
Midwifery subjects lost or ineligible (n=61), OB subjects lost or ineligible (n=51)
Sub-analysis of African American women (n=348)
Patients randomized to OB care (n=730); <grade 12 61.7%, 10-19 risk score 74.8%, smoking>11 cig./day 25.0%
Sub-analysis of African American women (n=370)
Power of 90% (a=0.05) to detect significant reduction in odds of LBW from 13% to 8%
Primary outcome: LBW, secondary outcome: VLBW
Inclusion:
  • –

    attended a state-funded prenatal clinic

  • –

    scored >10 at the first prenatal visit on a scale measuring risk of LBW due to social factors and previous medical risk, and/or had a LBW infant in their last pregnancy

  • –

    no known medical or pregnancy complications at entry

  • –

    live-born singleton

Abbreviations: PTB preterm birth; AA African American, OR odds ratio; nssd non-statistically significant difference, LBW low birthweight; CI confidence interval; SGA small for gestational age birth; OB obstetrician; ITT intent to treat analysis; CNM certified nurse-midwife; RD risk difference, VLBW very low birthweight; NICU neonatal intensive care unit; MD medical doctor; RR relative risk

a

Reference group is physician-led care; adjusted effect measures reported unless otherwise noted.

b

PTB birth at <36 wks.

c

LBW<2500 g.

d

PTB<37 completed wks. gestation.

e

SGA <10th percentile.

f

VLBW < 1500 g.

g

PTB<36 wks. gestation.

h

Undefined.

i

LBW<2500 g.