EAL

BF: Artificial Nipple and Duration of Breastfeeding (2008)

Citation:

Vogel A, Hutchison BL, Mitchell EA. Factors associated with the duration of breastfeeding. Acta Paediatr. 1999; 88: 1,320-1,326.

PubMed ID: 10626515

Study Design:

Longitudinal cohort study

Class:

B - Click here for explanation of classification scheme.

Quality Rating:

POSITIVE: See Quality Criteria Checklist below.

Research Purpose:

This cohort study of healthy term infants was conducted to identify factors associated with breastfeeding duration.

Inclusion Criteria:

Mothers were eligible for inclusion in the study if they delivered a normal term infant at North Shore Hospital, a public hospital in Auckland, New Zealand, that includes a level one obstetrics unit.

Exclusion Criteria:

The sample excluded multiple births, small-for-gestational age infants and infants with congenital anomalies. The participation rate was 79%. The reasons for non-participation are not known, but may include more mothers who chose not to breastfeed.

Description of Study Protocol:

Recruitment

The sample was taken from the hospital population, but because only 2% of births occur outside a hospital, this sample represents the general population. A systematic sample of alternate eligible mothers was invited to participate in the study. 79% of eligible mothers agreed to participate. Recruitment continued until the predetermined sample of 350 mothers had been admitted into the study. The study was approved by the North Shore Hospital Health Ethics committee.

Design

Longitudinal cohort.

Statistical Analysis

Statistical analysis used Kaplan-Meier survival curves and Cox regression for breastfeeding duration expressed in months to adjust for potential confounders
Factors significant on univariate analysis were included in the multivariate model. Variables were removed in a backward stepwise fashion, according to the strength of the association in the model, with P<0.1 as the cutoff for inclusion.
For an exposure with prevalence of 20% (such as maternal return to full-time work in the first year) a sample size of 300 was calculated to be sufficient to detect a relative risk of 1.8, with a 5% level of significance and 80% power. It was decided to recruit 350 participants to allow for potential loss to follow-up.

Data Collection Summary:

Timing of Measurements

Mothers were interviewed in the immediate postpartum period (usually in the first 48 hours) in the maternity ward
Mothers who were discharged home early were interviewed at home
Telephone interviews were conducted when the infants were one, two, three, six, nine and 12 months of age
Interviews used a standardized questionnaire, with pre-coded as well as open-ended questions. Comprehensive data were collected on feeding plans and outcomes.

Dependent Variables

Factors associated with breastfeeding duration

Full breastfeeding was defined as infants receiving breast milk with or without supplements of water or juice, but without formula, other milk or solids
Mastitis was defined as the mother's self-report of mastitis or breast infection.

Independent Variables

Demographic characteristics: Maternal age, parity, education, ethnicity, marital status, income
Obstetric factors: Smoked during pregnancy, Cesarean section, epidural
Infant factors: Sex (male); birth weight up to 3.5kg.

Description of Actual Data Sample:

Initial N: 350 mother-infant pairs
Attrition (final N): 95% of participants were followed up until 12 months of age, and only five (1.4%) were lost to follow-up while still breastfeeding. This included one infant who died at the age of nine months.
Age: 11% younger than 25 years; 69% 25 years to 34 years; 19% 35 years or older
Ethnicity: Caucasian women, population typically served by North Shore Hospital
Anthropometrics: No data
Location: North Shore Hospital, Auckland, New Zealand.

Summary of Results:

After adjustment for potential confounders, maternal age younger than 25 was associated with a shorter duration of breastfeeding. Other factors of significance in the multivariate analysis were the use of any formula anytime in the first month and the daily use of a dummy during the first month.

Table: Number of Subjects and Univariate and Multivariate Relative Risks for Shorter Duration of Breastfeeding and Their 95% Confidence Interval: Child-Care Variables.

		N (%)	Univariate RR	95% CI	Multivariate RR ^a	95% CI
Maternal Age (Years)	<25	39 (11.4)	2.21	1.38, 3.52	2.33	1.33, 4.05
	25-34	237 (69.1)	1.40	0.99, 1.97	1.45	1.01, 2.09
	≥35	67 (19.5)	1.00		1.0
Use of Dummy in the First Month	Yes	94 (28.3)	2.06	1.55, 2.75	1.62	1.20, 2.18
Use of Dummy in the First Month	No	238 (71.6)	1.00		1.00
Share Mother’s Bed at Three Months	Most of the night	13 (3.8)	0.38	0.16, 0.93	0.30	0.11, 0.83
	For breastfeeding only	152 (44.3)	0.83	0.64, 1.08	0.82	0.62, 1.09
	No	178 (51.9)	1.00		1.00
Share Room with Mother at Three Months	Yes	178 (51.9)	0.66	0.51, 0.85	0.69	0.51, 0.92
Share Room with Mother at Three Months	No	165 (48.1)	1.00		1.00
Formula Before One Month	Yes	106 (30.9)	3.08	2.36, 4.00	2.79	2.05, 3.80
Formula Before One Month	No	237 (69.1)	1.00		1.00

^a Adjusted for maternal age (younger than 25, 25 to 34), marital status, parity, income, full-time work, smoking, planed time of cessation of breastfeeding, inverted nipples, self-reported mastitis, daily use of dummy in the first month, sharing bedroom with mother at three months, bed-sharing with mother at three months.

Other Findings

The sample was predominantly European and middle-class and is typical of the deliveries at North Shore Hospital
The most common reason given by mothers for stopping breastfeeding was perceived insufficient milk
On univariate Cox regression, younger maternal age and return to full-time work in the first year was associated with shorter duration of breastfeeding
Obstetric and infant factors did not influence the duration of breastfeeding
Breastfeeding plans described by the mother at the time of delivery were significantly associated with the duration of breastfeeding. Mothers who stated that they planned to cease breastfeeding by six months of age and those who replied “don’t know” breast fed for a significantly shorter time. Mothers who stated that they planned to cease breastfeeding at a specific time after six months had the longest duration of breastfeeding.
Inverted nipples and perceived insufficient milk supply were associated with shorter duration of breastfeeding. Supplementation was associated with a shorter duration of breastfeeding.

Author Conclusion:

The sample excluded multiple births, small-for-gestational age infants and those with congenital anomalies. The participation rate was 79%. The reasons for non-participation are not known, but may include more mothers who choose not to breastfeed.
For an exposure with prevalence of 20% (such as maternal return to full-time work in the first year) a sample size of 300 was calculated to be sufficient to detect a relative risk of 1.8, with a 5% level of significance and 80% power. It was decided to recruit 350 participants to allow for potential loss to follow-up.
Excellent follow-up of cohort was achieved. Cox regression is a powerful technique for the analysis of survival of breastfeeding, as it effectively uses the data available from all time points.
Adjusted risk ratios of shorter duration of breastfeeding included daily dummy use 1.62 (1.20, 2.18).
Recommended that during the antenatal period attention be directed at mother’s plan for duration of breastfeeding, that mothers be encouraged to have their baby in the bedroom, and the use of formula and dummies should be discouraged in the first month of life.

Funding Source:

Reviewer Comments:

The limitations and critique of the study as stated by the authors seem appropriate.

Analytical longitudinal surveys refer to what epidemiologists term prospective or cohort studies. A cohort study is a study in which patients who presently have a certain condition or receive a particular treatment are followed over time and compared with another group that is not affected by the condition under investigation. Studies of this kind provide a better opportunity than one-time cross-sectional studies to examine whether certain behaviors do in fact lead to (or cause) the disease.

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?	Yes
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?	N/A
	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?	Yes
	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?		N/A
	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.)	N/A
	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?		Yes
	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?	N/A
	6.4.	Was the amount of exposure and, if relevant, subject/patient compliance measured?	N/A
	6.5.	Were co-interventions (e.g., ancillary treatments, other therapies) described?	N/A
	6.6.	Were extra or unplanned treatments described?	N/A
	6.7.	Was the information for 6.4, 6.5, and 6.6 assessed the same way for all groups?	N/A
	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?	Yes
	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?	Yes
	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)?	Yes
	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?	Yes
	8.7.	If negative findings, was a power calculation reported to address type 2 error?	N/A
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?	Yes
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