Table 1

Characteristics of the studies included in the systematic review

First author, yearCountryData collection periodNStudy designData collection siteData collection sourceMother’s socioeconomic statusQuality of the study
Lung function
Hanrahan, 199230USA25 March 1986–1 May 1989253Prospective cohortEast Boston Neighborhood Health Center.Interview, questionnaire and appointment. A questionnaire was collected at 2–4 weeks after birth. Lung function testing was performed at 4.2 weeks after birth.Not reported.8
Stick, 199631Australia1990–1991461Prospective cohortAntenatal clinic at King Edward Memorial Hospital.Questionnaire and appointment. Data collected as close as 48 hours after delivery as possible.Not reported.8
Lødrup Carlsen, 199732NorwayJanuary 1992–April 1993802Prospective cohortTwo leading birth clinics at Ulleval and Aker hospitals.Lung function was performed in as many babies as possible during the day. Lung function was measured at 2 days of life.Education
>12 years: 12
12–15 years: 55
>15 years: 14
8
Young, 200033AustraliaMay 1987–December 1991237Prospective cohortAntenatal clinic at Osborne Park Hospital.Interview, questionnaire and appointment. Lung function was measured at 1, 6 and 12 months of age.Not reported.6
Bisgaard, 200934Denmark1998–2001411Prospective cohortCOPSAC (Copenhagen Prospective Studies on Asthma in Childhood) clinical research unit.Personal interview, questionnaire and appointment. Lung function parameters were collected no later than 1 month after birth.Education:
At most college: 234
Medium: 99
University: 51
8
Owens, 201835Australia1987–1990235Retrospective cohortPrincess Margaret Hospital.Questionnaire and appointment. Lung function testing done at 1, 6 and 12 months of age.
Not reported.9
Apnoea
Gunnerbeck, 201136Nordic countries1999–2006609 551Retrospective cohortSwedish Medical Birth Register.Medical records. Children were younger than 6 months of life.Education years:
≥9 years: 27%
≥10 cigarettes/day: 34%
7
Ramos-Fernández, 201837Southern EuropeJanuary 2010–December 2015147Case–controlTertiary hospital in Southern Europe.Medical records. Included only newborns.Not reported.5
Wheezing
Gold, 199938USASeptember 1994–June 1996505Prospective cohortHome visits.Questionnaires. Home visit at 2–3 months of age and questionnaires were applied every 2 months.Family income:
>$50 000: 352
$30 000–$50 000: 88
$30 000: 43
Unknown: 16
8
Henderson, 200139UK, Czech Republic199914 369Retrospective cohortSelf-administered questionnaires at home.Self-reported questionnaire. Questionnaires were applied at 6 months of age.Not reported.6
Murray, 200440UKOctober 1995–July 1997369Prospective cohortHome visits.Questionnaire. Home visits made after birth and at 1 year of age.Not reported.6
Borrego, 200941Portugal and LondonSeptember 2005–September 200780Case–controlOutpatient clinic in Hospital Dona Estefania, Lisbon and children recruited to epidemiological studies at UCL (University College London) Institute of Child Health, London, UK.Questionnaire. Infants with recurrent wheeze.Not reported.6
Hunt, 201142USAApril 2001–August 2001103Prospective cohortHome visits.Interval questionnaire administration, physical examination and collection of a urine specimen. Collected data of infants from 1 to 11 months of age. Questionnaires were applied every 3 months.Education:
At least high school: 55%
Less than high school: 45%
7
Duijts, 201243The NetherlandsApril 2002– January 20063867Prospective cohortQuestionnaires completed at home.Questionnaire about active smoking data and questionnaires with parental report of wheezing. Questionnaire was applied at 1 year of age.The first trimester of pregnancy only smoking group:
Primary or secondary: 48.1% (204)
Higher: 51.7% (219)
Missing: 0.2% (1)
Continued smoking group:
Primary or secondary: 72.3% (460)
Higher: 25.2% (160)
Missing: 2.5% (16)
6
Fuentes-Leonarte, 201544Spain2003–20082039Prospective cohortHospital visits at the third trimester of pregnancy and at first year of life of the infant.A structured questionnaire administered to the parents by paediatricians. A questionnaire was applied at 14.8 months of age, asking about the first 12 months of life.Socioeconomic status:
CS I+II*: 52
CS III†2: 84
CS IV+V‡:193
Education:
Primary: 125
Secondary: 160
University: 43
8
van der Zalm, 201145The NetherlandsNot reported1105Prospective cohortQuestionnaire completed at enrolment. Lung function measured at the hospital when the child is less than 2 months old.Questionnaire. Included infants at the age of 2–3 weeks of age, before any respiratory symptoms have occurred, and followed until they reached 1 year of age.Not reported.7
Tariq, 200022UKJanuary 1989–February 19901456Prospective cohortSt Mary’s Hospital.Hospital records and appointment. Included records of children who had asthma at 1 year of age.Not reported.9
Davidson, 201023UK1963–1999, and 1975–1999248 612Retrospective cohortTwo health districts of Oxfordshire and West Berkshire.Hospital records from children admitted for asthma from 0 to 12 months of age.Socioeconomic status:
CS I+II*0: 29.7%
CS III†: 48.1%
CS IV+V‡2: 22.2%
7
Goudarzi, 201846Japan2003–20123296Prospective cohortQuestionnaires conducted by investigators during pregnancy, medical birth records and self-administered questionnaire at home.Medical birth records, self-administered questionnaire 4 months after delivery, postnatal questionnaires collected at age 1 and ISAAC (International Study of Asthma and Allergies in Childhood) questionnaire. The postnatal questionnaire was collected at 1 year of age.Not reported.7
Gray, 201947Australia20131074Prospective cohortLocal hospital at region of Barwon Area, Victoria, Australia.Self-administered questionnaire and medical records checked when available. A validated questionnaire was collected at 1, 3, 6, 9 and 12 months. Parents reported on any wheeze episodes since the previously completed review.Low: 357 (33.2%)
Middle: 353 (32.9%)
High: 351 (32.7%)
Unknown: 13 (1.9%)
8
Lundholm, 202048Sweden2005–2015788 508Prospective cohortBased on national registry data.Data regarding smoking in pregnancy were retrieved from the Medical Birth Register, and outcomes data were retrieved from the Swedish Prescribed Drug Register and the National Patient Register.Father’s disposable income:
First quintile: 76% non-smokers vs 10.4% smokers.
Second quintile: 78.4% non-smokers vs 8.1% smokers.
Third quintile: 79% non-smokers vs 6.5% smokers.
Fourth quintile: 80.7% non-smokers vs 4.7% smokers.
7
  • *SC (social class) I+II: managerial and senior technical staff, intermediate occupations and commerce managers.

  • †SC (social class) III: skilled non-manual workers.

  • ‡SC (social class) IV + V: skilled and partly-skilled manual workers and unskilled manual workers