Background
Methods
Primary objective
Primary outcome
Search strategy
Study selection and data abstraction
Statistical analysis
Primary analysis
Subgroup analyses
Heterogeneity assessment
Quality assessment
Results
Database search results
Characteristics of studies included in the review
Study, year | Country/ Study design | Study period/ Follow-up | Data source | Total sample | Interval used | Statistical tests used | Indication for Caesarean | Parity | Exclusions |
---|---|---|---|---|---|---|---|---|---|
Eijsink, 2008 [32] | Holland / Cohort | 1998-2002/ Follow-up to 2005 | Single hospital database | 547 | IPI (scale) | Kaplan-Meier curves | Breech emergency & elective | Primiparous | Multiple deliveries, congenital malformations, uterine anomalies |
Collin, 2006 [10] | Sub-Saharan Africa / Cohort | 1993-2003/ Minimum follow-up 3 years | Cross-sectional standardised survey data from 22 countries | 35,398 | IPI ( >1 or <5 years) | Cox regression | No | Multiparous | Women with >1 terminated pregnancy; women currently breastfeeding; abstaining from intercourse or using contraception; women in South Africa (due to high elective Caesarean rates); stillbirths; women outside 14–49 years of age |
Smith, 2006 [18] | Scotland / Cohort | 1980-1984/ Follow-up to 1999 | Population-based database | 109,991 | IPI (scale) | Logistic regression | Emergency, elective for breech, all other pre-labour Caesarean | Primiparous | Multiple births, preterm births, perinatal deaths, missing values |
Murphy, 2002 [7] | UK / Cohort | 1991-1992/ Minimum follow-up 3 years | Self-completed questionnaire data | 3,994 | IPI (>1 or >3 years) | Logistic regression | No | Multiparous | Women with unplanned pregnancies |
Zdeb, 1984 [33] | USA/ Cohort | 1975/ Follow-up for 5 years | Single hospital database | 5,513 | IPI (scale) | X2 analysis | No | Primiparous | Stillbirths, high-forceps, mid-forceps, breech, version and extraction deliveries |
Tollånes, 2007 [16] | Norway/ Cohort | 1969-1996/ Follow-up to 2003 | Nationwide Birth Register | 596,341 | BI (scale) | Logistic regression | Breech, pre-eclampsia, low-risk Caesarean groups | Primiparous | Women dying aged <50, women who changed partners, multiple pregnancies |
Tower, 2000 [17] | UK / Cohort | 1992-1993/ Follow-up for 5 years | Single hospital database | 1,152 | BI, IPI (scale) | Not stated | Failure to progress, fetal distress | Primiparous | None stated |
Huttly, 1990 [34] | Brazil/ Cohort | 1982/ Follow-up for 4 years | Data obtained from interview of mothers | 4,683 | BI (within 35–52 months) | Not stated | No | Multiparous | Tubal ligation/ sterilisation |
Hemminki,1987 [37] | Sweden/ Cohort | 1973, 1976/ Follow-up for 5 years | Nationwide Birth Register survey data | 12,918 | BI (<5 years) | X2 analysis | No | Primiparous | Hysterectomy, non-Swedish women, rare blood groups, multiple pregnancies, malformations, birth weight <2000g, perinatal death |
LaSala, 1987 [35] | USA/ Case control | 1978/ Follow-up for 3 years | Single hospital logbook | 570 | BI (>2 years) | X2 analysis | No | Primiparous | Missing hospital records, sterilisation, women using contraception |
Hemminki,1985 [36] | USA/ Cohort | 1957-1982/ Minimum 1 year follow-up, maximum 25 years | Nationwide Birth Register | 812 | BI (scale) | Kaplan-Meier curves | No | Primiparous | Women outside 15–44 years of age; women living in Alaska or Hawaii; women with no live births or more than two abortions; multiple births; missing data; perinatal deaths; birth weight <1500g; women who put their child up for adoption |
Primary outcome analysis
Subgroup analyses
Study characteristic | Number of studies included | Pooled OR estimate (95% CI) | I2% |
---|---|---|---|
Overall pooled estimate
| n = 5 | 0.90 [0.86, 0.93] | 30% |
Parity
| |||
Primiparous women only | n = 2 | 0.91 [0.87, 0.96] | 0% |
Not limited to primiparous women | n = 3 | 0.81 [0.73, 0.90] | 0% |
By publication date
| |||
Pre-2000 | n = 1 | 0.80 [0.68, 0.94] | NA |
Post-2000 | n = 4 | 0.90 [0.86, 0.94] | 19% |
Length of follow-up
| |||
<10 years | n = 3 | 0.81 [0.73, 0.90] | 0% |
>10 years | n = 2 | 0.91 [0.87, 0.96] | 0% |
Indication for mode of delivery
| |||
Specified* | n = 2 | 0.92 [0.88, 0.97] | 88% |
Not specified | n = 3 | 0.81 [0.73, 0.90] | 0% |
By cohort size
| |||
<35,000 | n = 2 | 0.79 [0.67, 0.92] | 0% |
>35,000 | n = 3 | 0.90 [0.87, 0.95] | 13% |
By definition of sub-fertility used
| |||
a. Birth Interval (BI) | n = 2 | 0.89 [0.84, 0.94] | 44% |
Inter-pregnancy interval (IPI) | n = 3 | 0.91 [0.85, 0.97] | 45% |
b. Categorical measure (e.g. > 3 years) | n = 3 | 0.81 [0.73, 0.90] | 0% |
Continuous measure (e.g. median IPI) | n = 2 | 0.91 [0.87, 0.96] | 0% |
Results of studies included in the systematic review (but not the meta-analysis)
Inter-pregnancy interval (IPI)
Study | Main Findings | Conclusions |
---|---|---|
Eijsink et al., 2008 [32] |
Median IPI: Elective CS breech (22mths), Emergency CS (18 mths), Vaginal breech (16 mths), Reference [home birth] (18 mths) | In women with a breech delivery, a longer IPI among the elective CS group was reported, however there were only 35 women in this group |
Zdeb et al., 1984 [33] |
Median IPI in mths: 21.8 | No significant difference in the timing of subsequent pregnancies among the two groups |
#Tower et al., 2000 [17] |
Median BI (IQR) in mths: CS failure to progress (32, 23–45); CS fetal distress (34, 25–46); SVD (32, 23–44) | No evidence that women delivering by Caesarean section have significantly longer waiting times to next pregnancy or birth |
Median IPI (IQR) in mths: CS failure to progress (28, 22–40); CS fetal distress (31, 24–44); SVD (29, 22–39) | ||
Hemminki, 1987 [37] |
BI: Subsequent pregnancy within 5 years 1973 cohort- RR (0.91, 95% CI 0.89, 0.93); 1976 cohort RR (0.91, 95% CI 0.89, 1.12) | Proportion of women with a previous Caesarean section less likely to have a subsequent delivery, although no significant difference found |
LaSala, 1987 [35] |
BI: CS delivery (5.5%) >2 years without conceiving; vaginal delivery (1.4%) >2 years without conceiving | Women with a previous Caesarean were less likely to have a subsequent birth and took longer to conceive than women with a previous vaginal delivery. However the sample size was very small |
Hemminki et al., 1985 [36] |
Median BI (mths): CS delivery (44.4); vaginal delivery (45.6) | No significant difference in waiting time to next birth among women with a previous Caesarean section compared to women with a previous vaginal delivery |
Birth interval (BI)
Heterogeneity assessment
Quality assessment
Study | Selection bias | Exposure bias | Outcome assessment bias | Confounding factor bias* | Analytical bias | Attrition bias | Overall likelihood of bias |
---|---|---|---|---|---|---|---|
Eijsink et al., 2008 [32] | Moderate | Low | Low | High (no adjustment for confounders reported, matched by maternal age and date of delivery) | Low | Minimal | High |
Collin et al., 2006 [10] | Low | Low | Low | Minimal (adjusted for age, parity, level of education, urban or rural residence and young age at first intercourse) | Minimal | Low | Low |
Smith et al., 2006 [18] | Minimal | Low | Low | Minimal (adjusted for marital status, deprivation, birth weight, infant sex, maternal age, maternal height and method of induction) | Minimal | Minimal | Low |
Murphy et al., 2002 [7] | Low | Low | Low | Minimal (adjusted for maternal and paternal age, co-habitation, oral contraceptive pill use, cigarette exposure, alcohol consumption, educational level, ethnicity, parity, change of partner, maternal BMI) | Minimal | Minimal | Low |
Zdeb et al., 1984 [33] | Low | Low | Low | Moderate (none reported). Matching by race, complications of pregnancy, maternal education and maternal age | Moderate | Low | High |
Tollånes et al., 2007 [16] | Minimal | Low | Low | Minimal (stratified by maternal age, level of education and infant survival). Sub-group analyses by low-risk group, pre-eclampsia and breech presentation | Low | Minimal | Low |
Tower et al., 2000 [16] | Low | Low | Low | Moderate (no adjustment for confounding). Matching by age and date of delivery | Moderate | Moderate | High |
Huttly et al., 1990 [34] | Low | Low | Low | Minimal (adjusted for income, age, education and parity) | Moderate | Moderate | Low |
Hemminki, 1987 [37] | Low | Low | Low | Moderate (no adjustment for confounders). Matching by year of birth, maternal age and infant sex | Moderate | Low | High |
LaSala et al., 1987 [35] | Moderate | Low | Minimal | Moderate (no adjustment for confounding reported). Matching by age and parity | Moderate | Moderate | High |
Hemminki et al., 1985 [36] | Low | Low | Minimal | Moderate (no adjustment reported). Matching by date of birth, mother’s age, race and marital status | Moderate | Minimal | High |