Health Disparities

HD: Effectiveness of Nutrition Intervention Methods (2010)


Furman L, Minich N, Hack M. Correlates of lactation in mothers of very low birth weight infants. Pediatrics. 2002 Apr; 109 (4): e57.

PubMed ID: 11927730
Study Design:
Prospective Cohort Study
B - Click here for explanation of classification scheme.
Quality Rating:
Neutral NEUTRAL: See Quality Criteria Checklist below.
Research Purpose:

The purpose of this study was to determine the correlates of intent to breastfeed and of successful lactation and nursing at the breast in mothers of very-low birth weight (VLBW) infants.

Inclusion Criteria:
  • Singleton birth
  • Birth weight between 600 and 1,499 grams
  • Gestational age less than 33 weeks
  • Absence of:
    • Positive drug screen
    • Major congenital anomaly
    • Intrauterine infection
    • Overwhelming maternal social factors.
Exclusion Criteria:
  • Multiple birth
  • Birth weight less than 600 grams or more than 1,499 grams
  • Gestational age more than 32 weeks
  • Positive drug screen
  • Major congenital anomaly
  • Intrauterine infection
  • Overwhelming maternal social factors
  • Critical illness or death before enrollment
  • Maternal illness.
Description of Study Protocol:


Mothers recruited from the neonatal intensive care unit at Rainbow Babies and Children's Hospital (Cleveland, OH).


  • Eligible mothers who agreed to participate in the study were followed until their infants were four months' of age (corrected age [CA])
  • Mothers completed questionnaires pertaining to intent to breastfeed or formula feed, social supports and lactation at enrollment (three weeks after delivery), at 35 weeks', 40 weeks' and four months' CA.


  • Not applicable
  • Per nursery policy, all mothers of pre-term infants were encouraged to provide breast milk for their infants.

Statistical Analysis

  • T-test to compare continuous measures
  • Chi-square or Fisher exact test to compare categorical data
  • Non-parametric continuous data were analyzed with the Mann-Whitney U test
  • Multiple logistic regression was performed to examine the association between correlates of continued lactation beyond 40 weeks' CA while controlling for associated demographic factors.
Data Collection Summary:

Timing of Measurements

  • Enrollment: Three weeks after delivery
  • 35 weeks' (gestational age)
  • 40 weeks' (gestational age)
  • Four months' (corrected age).

Dependent Variables

  • Intent to breastfeed
  • Continued lactation (defined as continuing to express or pump breast milk and/or attempting to nurse the infant at the breast).

Independent Variables

  • Maternal descriptors
    • Age
    • Race
    • Marital status
    • Education
    • Duncan score (socioeconomic index based on occupation)
    • Out-of-home employment
    • Other children
    • Breastfed other child
    • Personal health ratings
    • Rates of depressive symptoms
  • Current obstetrical history
    • Inborn
    • Maternal transport
    • Preeclampsia
    • Antepartum hemorrhage
    • Prenatal steroids
    • Cesarean section
  • Birth data
    • Birth weight
    • Gestational age
    • Gender
    • Apgar
    • Small for gestational age (SGA)
  • Neonatal morbidity
    • Chronic lung disease
    • Ventilator dependence
    • Apnea of prematurity
    • Sepsis
    • Necrotizing enterocolitis
    • Abnormal cranial ultrasounds
    • Hospital stay
  • Family factors
    • Have other children
    • Breastfed previous child
    • One or more children up to age six years old at home
    • Father of the baby
      • Involved
      • Employed
      • Supports breastfeeding
  • Kangaroo care
    • Heard of kangaroo care
    • Tried kangaroo care
  • Decision to breastfeed
    • Timing
      • Before pregnancy
      • During pregnancy
      • After delivery
    • Desire to breastfeed
    • Breastfeeding satisfaction
  • Milk expression
    • Began less than six hours after delivery
    • Expressed five times or more per day
    • Mean volume per pumping
    • Owned or rented an electric pump
    • Electric pump covered by insurance
  • Bottle feeding
    • Baby's age first nipple fed by bottle
  • Nursing factors
    • Always a let-down sensation with pumping
    • Infant to breast by 35 weeks CA
    • Always a let-down sensation with nursing
    • Baby's age first breastfed
    • Postnatal age of first latch-on
    • Infant always latches on
    • Frequency of breastfeeds.


Questionnaires measured sociodemographics and factual and emotional aspects of the breast- and bottle-feeding experience.

Maternal and infant prenatal, birth and neonatal data were gathered from the medical record at discharge.

Nutritional intake recorded daily at the hospital; after discharge, mothers were asked to keep a 72-hour food diary before the 40-week and four-month CA interviews.


Description of Actual Data Sample:
  • Initial N: 119
    • 32 intend to formula feed
    • 87 intend to breastfeed
  • Attrition (final N): 112
    • 29 formula feeding
    • 69 discontinued lactation
    • 14 mothers still lactating
  • Age: Mean age in years ± standard deviation (SD)
    • Intent to breastfeed: 28±7
    • Intent to formula feed: 26±6
    • Continued lactation at 40 weeks' CA: 31±7
    • Discontinued lactation at 40 weeks' CA: 26±7
  • Ethnicity: Race (N, percent white)
    • Intent to breastfeed: 39 (45)
    • Intent to formula feed: 12 (38)
    • Continued lactation at 40 weeks' CA: 19 (63)
    • Discontinued lactation at 40 weeks' CA: 20 (35)
  • Other relevant demographics:
    • Mothers who intended to breastfeed were significantly more likely than those who intended to bottle feed to:
      • Be married
      • Have more than a high school education
      • Have a higher Duncan score
      • Have no other children
    • Mothers who continued lactation at 40 weeks' CA were significantly more likely than those who did not continue lactation to:
      • Be older
      • Be white
      • Be married
      • Have more than a high school education
      • Have a higher Duncan score
  • Anthropometrics:
    • Infants of mothers who intended to formula feed were significantly heavier and older (gestational age) than infants of mothers who intended to breastfeed
    • There was no significant difference, however, in birth weight or gestational age between infants of mothers who continued or discontinued lactation at 40 weeks' CA
  • LocationCleveland, OH.
Summary of Results:


Key Findings

Variables Continued Lactation at 40 Weeks' CA
Discontinued Lactation at 40 Weeks' CA
Age (mean in years ± SD) 31±7 26±7  <0.01
Race (N, percent white) 19 (63) 20 (35) 0.02
Marital status (N, percent married) 24 (80) 22 (39)  <0.001
Education (N, percent with greater than high school) 21 (70) 24 (42) 0.02
Duncan score (mean ± SD) 42±16 31±13  <0.01
Heard of kangaroo care (N, percent) 28 (93) 40 (70) 0.03
Of those who heard of it, those who tried it (N, percent) 25 (89) 24 (60) 0.02
Timing of breastfeeding decision      <0.01
Before pregnancy (N, percent) 19 (63) 16 (28)  
During pregnancy (N, percent) 9 (30) 23 (40)  
After delivery (N, percent) 2 (7) 18 (32)  
Desire to breastfeed (1=very much, 5=not at all) (mean±SD)  1.1±0.5 1.8±1.0  <0.001
Breastfeeding satisfaction (1=very much, 5=not at all) (mean±SD)  1.2±0.4 1.8±0.9  <0.001
Began milk expression less than six hours after delivery (N, percent) 9 (30) 5 (9) 0.02
Expressed five times or more per day at initial interview 26 (87) 36 (63) 0.04
Mean volume in mL of milk per pumping at initial interview (± SD)  126±75 66±45  <0.001
Mean volume in mL of milk per pumping at 35 weeks CA (±SD)  132±75 54±40 <0.001
Infant to breast by 35 weeks CA (N, percent) 29 (97) 14 (74) 0.03
Frequency of breastfeeds (mean per day ± SD) 1.4±1 0.8±0.6 0.04


Other variables were not significantly associated with continued lactation at 40 weeks' CA.

With multiple regression analysis controlling for maternal age, race, marital status and education beyond high school, the following correlates were significantly associated with continuing lactation beyond 40 weeks' CA:

  • Practice of kangaroo care (P<0.01)
  • Beginning milk expression before six hours after delivery (P<0.02)
  • Expressing milk more than five times per day at initial interview (P<0.04
  • Mean ounces expressed per day at initial interview (P<0.001)
  • Putting the infant to the breast by 35 weeks CA (P<0.001).

Other Findings

  • No significant differences between mothers who continued lactation beyond 40 weeks' CA and those who discontinued in:
    • Out-of-home employment
    • Personal health ratings
    • Rates of depressive symptoms
  • 14 mothers were still lactating at four months' CA
    • Because number of nursing mothers was small, data analyses were not performed.
Author Conclusion:

Intent to breastfeed before delivery and maternal factors indicative of higher socioeconomic status were significantly associated with the decision to breastfeed and its success beyond 40 weeks. Other important factors related to lactation beyond 40 weeks included initiating milk expression at less than six hours after delivery, expressing five or more times per day, practicing kangaroo care and putting the infant to the breast more often. Perinatal factors, generalized social supports, access to a breast pump, depressive symptoms and rate of maternal employment did not seem to affect continuation of lactation beyond 40 weeks' CA. 

Funding Source:
Government: National Institutes of Health
Medela Corporation
University/Hospital: Rainbow Babies and Childrens Hospital Faculty Fund, Rainbow Babies and Childrens Hospital Board of Trustees
Saint Luke's Foundation of Cleveland
Other non-profit:
Reviewer Comments:

It would be difficult to include all possible confounding factors or determinants of lactation, such as pediatrician's encouragement for the use of breast milk, for example. I would have liked to have seen infant's age at discharge, as it would seem that the encouragement of staff to pump while the infant is in the hospital may be a confounding factor. The questionnaire used had not been validated, which also detracted from the quality of the study. 

Quality Criteria Checklist: Primary Research
Relevance Questions
  1. Would implementing the studied intervention or procedure (if found successful) result in improved outcomes for the patients/clients/population group? (Not Applicable for some epidemiological studies) Yes
  2. Did the authors study an outcome (dependent variable) or topic that the patients/clients/population group would care about? Yes
  3. Is the focus of the intervention or procedure (independent variable) or topic of study a common issue of concern to dieteticspractice? Yes
  4. Is the intervention or procedure feasible? (NA for some epidemiological studies) Yes
Validity Questions
1. Was the research question clearly stated? Yes
  1.1. Was (were) the specific intervention(s) or procedure(s) [independent variable(s)] identified? Yes
  1.2. Was (were) the outcome(s) [dependent variable(s)] clearly indicated? Yes
  1.3. Were the target population and setting specified? Yes
2. Was the selection of study subjects/patients free from bias? Yes
  2.1. Were inclusion/exclusion criteria specified (e.g., risk, point in disease progression, diagnostic or prognosis criteria), and with sufficient detail and without omitting criteria critical to the study? Yes
  2.2. Were criteria applied equally to all study groups? Yes
  2.3. Were health, demographics, and other characteristics of subjects described? Yes
  2.4. Were the subjects/patients a representative sample of the relevant population? ???
3. Were study groups comparable? Yes
  3.1. Was the method of assigning subjects/patients to groups described and unbiased? (Method of randomization identified if RCT) N/A
  3.2. Were distribution of disease status, prognostic factors, and other factors (e.g., demographics) similar across study groups at baseline? Yes
  3.3. Were concurrent controls or comparisons used? (Concurrent preferred over historical control or comparison groups.) N/A
  3.4. If cohort study or cross-sectional study, were groups comparable on important confounding factors and/or were preexisting differences accounted for by using appropriate adjustments in statistical analysis? Yes
  3.5. If case control study, were potential confounding factors comparable for cases and controls? (If case series or trial with subjects serving as own control, this criterion is not applicable.) N/A
  3.6. If diagnostic test, was there an independent blind comparison with an appropriate reference standard (e.g., "gold standard")? N/A
4. Was method of handling withdrawals described? Yes
  4.1. Were follow-up methods described and the same for all groups? ???
  4.2. Was the number, characteristics of withdrawals (i.e., dropouts, lost to follow up, attrition rate) and/or response rate (cross-sectional studies) described for each group? (Follow up goal for a strong study is 80%.) Yes
  4.3. Were all enrolled subjects/patients (in the original sample) accounted for? Yes
  4.4. Were reasons for withdrawals similar across groups? ???
  4.5. If diagnostic test, was decision to perform reference test not dependent on results of test under study? N/A
5. Was blinding used to prevent introduction of bias? No
  5.1. In intervention study, were subjects, clinicians/practitioners, and investigators blinded to treatment group, as appropriate? N/A
  5.2. Were data collectors blinded for outcomes assessment? (If outcome is measured using an objective test, such as a lab value, this criterion is assumed to be met.) No
  5.3. In cohort study or cross-sectional study, were measurements of outcomes and risk factors blinded? No
  5.4. In case control study, was case definition explicit and case ascertainment not influenced by exposure status? N/A
  5.5. In diagnostic study, were test results blinded to patient history and other test results? N/A
6. Were intervention/therapeutic regimens/exposure factor or procedure and any comparison(s) described in detail? Were interveningfactors described? ???
  6.1. In RCT or other intervention trial, were protocols described for all regimens studied? N/A
  6.2. In observational study, were interventions, study settings, and clinicians/provider described? Yes
  6.3. Was the intensity and duration of the intervention or exposure factor sufficient to produce a meaningful effect? Yes
  6.4. Was the amount of exposure and, if relevant, subject/patient compliance measured? ???
  6.5. Were co-interventions (e.g., ancillary treatments, other therapies) described? ???
  6.6. Were extra or unplanned treatments described? ???
  6.7. Was the information for 6.4, 6.5, and 6.6 assessed the same way for all groups? Yes
  6.8. In diagnostic study, were details of test administration and replication sufficient? N/A
7. Were outcomes clearly defined and the measurements valid and reliable? Yes
  7.1. Were primary and secondary endpoints described and relevant to the question? Yes
  7.2. Were nutrition measures appropriate to question and outcomes of concern? Yes
  7.3. Was the period of follow-up long enough for important outcome(s) to occur? Yes
  7.4. Were the observations and measurements based on standard, valid, and reliable data collection instruments/tests/procedures? No
  7.5. Was the measurement of effect at an appropriate level of precision? Yes
  7.6. Were other factors accounted for (measured) that could affect outcomes? No
  7.7. Were the measurements conducted consistently across groups? Yes
8. Was the statistical analysis appropriate for the study design and type of outcome indicators? Yes
  8.1. Were statistical analyses adequately described and the results reported appropriately? Yes
  8.2. Were correct statistical tests used and assumptions of test not violated? Yes
  8.3. Were statistics reported with levels of significance and/or confidence intervals? Yes
  8.4. Was "intent to treat" analysis of outcomes done (and as appropriate, was there an analysis of outcomes for those maximally exposed or a dose-response analysis)? N/A
  8.5. Were adequate adjustments made for effects of confounding factors that might have affected the outcomes (e.g., multivariate analyses)? Yes
  8.6. Was clinical significance as well as statistical significance reported? No
  8.7. If negative findings, was a power calculation reported to address type 2 error? No
9. Are conclusions supported by results with biases and limitations taken into consideration? Yes
  9.1. Is there a discussion of findings? Yes
  9.2. Are biases and study limitations identified and discussed? No
10. Is bias due to study's funding or sponsorship unlikely? Yes
  10.1. Were sources of funding and investigators' affiliations described? Yes
  10.2. Was the study free from apparent conflict of interest? Yes