Table 1

Descriptive characteristics of included studies

First author and year of publication	Countr(ies) and time of data collection	Study objective	Study design	Description of study area	Sample selection criteria and total study sample size	Sample size of adolescents and definition of adolescents
Nath et al 46 1993	India 1987–1989	Analyse breast feeding, the mechanisms that influence postpartum amenorrhoea, and the role of biological and sociocultural variables on resumption of postpartum menstruation in traditional Indian society using data collected in two states. Focus on roles of women’s age and child’s sex on duration of postpartum amenorrhoea	Cross-sectional retrospective study using household surveys	Areas of Karimganj district Assam (only scheduled castes) and eastern Uttar Pradesh	Married female mambers of sampled households, residing in studied area, not using family planning, woman not menopausal, both partners alive and woman <50 years; n=1449 in Assam and n=3702 in Uttar Pradesh	685 adolescents <20 years (233 in Assam and 452 in Uttar Pradesh) at the time of child’s birth
Bhattacharya et al 45 1995	India 1987–1988	Examine and discuss the effects of some sociocultural and economic factors on the proximate determinants of fertility in rural areas of eastern Uttar Pradesh (mainly interested in caste and wealth)	Cross-sectional retrospective study of 4448 households in 3 districts, retrospective recall	Three districts in Uttar Pradesh (Varanasi, Ghazipur and Azamgarh)	Married women, both partners alive and woman <50 years old, n=3702 women in analysis of lactational amenorrhoea method by age	452 adolescents <20 years of age at birth of child
Haggerty and Rutstein52 1999	18 countries in Sub-Saharan Africa, 4 in Near East/North Africa, 7 in Asia, and 8 in Latin America/Caribbean; 1990–1996	Examine the range of durations of postpartum effects including postpartum amenorrhoea and the use of lactational amenorrhoea method	Cross-sectional retrospective study of households	Nationally representative surveys (DHS)	Women aged 15 to 49 years living in sampled households and gave live birth within last 5 years. Sample size differs by country	In age group 15–19 years, range from 115 (Khazakhstan) to 8448 (India). Age at time of child’s birth
Rahman et al 47 2002	Bangladesh 1993–1995	Examine the variation in suckling patterns, morbidity status of the mother and infant, introduction of weaning food, sociodemographic status and selected maternal anthropometric measurements in mother from a poor urban area of Dhaka, Bangladesh	Prospective longitudinal observational study	Dhaka (poor urban area)	Mothers age 17–37 years coming to a maternal and child health clinic for antenatal care during normal pregnancy, in third trimester, residing near Mirpur, intending to breast feed at least 6 months, had regular menstrual cycle prior to pregnancy, not intending to use hormonal contraception during study period. After birth, only vaginally delivered singletons gestational age ≥37 weeks were included. No information about marital status. n=97 mother–infant pairs	23 mother–infant pairs among mothers <20 years (age in completed years at time of antenatal care)
Rahman et al 2005	Bangladesh timing of data collection not stated	Analyse the knowledge on contraceptive method among currently married adolescents	Cross-sectional retrospective study, both quantitative and qualitative data collected	Both urban and rural areas of Bangladesh	Married adolescents aged 10–19 years, excluded currently pregnant, widowed, divorced and separated adolescents. N=1881 (all included study participants were adolescents). Combination of adolescents who have never had children and those who have (no distribution by parity provided)	1881 married female adolescents (123 were 10–14 years and 1758 were 15–19 years old). Age at survey
Audu et al 50 2006	Nigeria timing of data collection not stated	Evaluate the correct knowledge and utilisation of the natural family planning methods: rhythm method, lactational amenorrhoea method and coitus interruptus among a population with low utilisation of modern contraceptive methods	Cross-sectional retrospective household survey, all married women in selected households interviewed	Urban Maiduguri and rural Gwoza, Konduga, Madgali in northeastern Nigeria	Married women age 15–45 years in sampled households. N=886 women. Not all have had children	Sample size in age group 15–19 not provided. Age at time of survey
Türk et al 49 2010	Turkey 2006	Investigate the status of the use of lactatioonal amenorrhoea as a family planning method by women with 6-month-old infants and the factors influencing its use	Cross-sectional retrospective study using semi-structured interview form during home visits	Kars, eastern Anatolia	Women who delivered at a provincial maternity and children’s hospital in the city of Kars and had 6-month-old infants, living in both urban and rural areas. No information about marital status as inclusion criterion, but all women in the sample have non-missing descriptive data on husband’s education level. n=188 women	10 adolescents age <20 years at the time of survey
Singh et al 51 2012	India 2009	Investigate the nature and pattern of duration of postpartum amenorrhoea and to check the relative influences of various sociodemographic factors on it	Cross-sectional retrospective study using community-based household survey	Four valley districts of Manipur: Bishnupur, Thoubal, Imphal West, Imphal East	Ever-married women with at least one live birth (most recent live birth analysed). n=1225 women	Adolescents were included in two age groups (<15 and 15–20 years at time of marriage). Sample size of adolescents not provided
Kaplanoglu et al 48 2015	Turkey 2010–2012	Evaluate the postpartum contraception preferences and their efficiency in adolescents	Cross-sectional retrospective study comparing adolescents and older women	Adiyaman hospital	Primigravida patients who gave birth in Adiyaman University Hospital at least 12 months before. If adolescents <19 years, called by phone and invited to clinic for follow-up, if they had no medical or surgical problems. N=560 adolescents and 1046 women age 20–35 (not stated whether these were also primigravida)	506 adolesents age 10–19 years ‘during the study’