Table 1. Characteristics of 14 studies included in the E2C2 pooled analysis.
| Study | Location | Period of ascertainment | Cases (n) | Controls (n) | Age range (years)a | Matching parameters | Infertilityb prevalence in controls | Study-specific infertility definitionb |
|---|---|---|---|---|---|---|---|---|
|
Case-control | ||||||||
| Alberta Case-Control Study on Endometrial Cancer (ALBERTA) | Canada | 2002–2006 | 542 | 1032 | 28–79 | Age (±5 years) | 39% | Before the reference date, were there any periods of 12 months or longer when you could have become pregnant but did not? |
| Australian National Endometrial Cancer Study (ANECS) | Australia | 2005–2007 | 1444 | 741 | 26–80 | Age (5-year group), state | 24% | Have you ever had regular sexual intercourse without any kind of birth control for more than 1 year without getting pregnant? |
| Connecticut Endometrial Cancer Study (CECS) | USA | 2004–2009 | 668 | 665 | 35–80 | Age (5-year group) | 30% | Have you ever tried for at least 6 months to become pregnant, but were unable to (i.e., when you didn't use any contraception)? |
| Estrogen, Diet, Genetics, and Endometrial Cancer (EDGE) | USA | 2001–2005 | 469 | 467 | 23–97 | Age (5-year group) | 45% | Did you ever have unprotected intercourse, once a week or more often, for a period of 6 months or longer without getting pregnant? |
| Hawaii Endometrial Cancer Study (HAW) | USA | 1988–1993 | 332 | 511 | 27–80 | Age (±2.5 years), ethnicity | 12% | Have you ever tried to become pregnant for 2 straight years or more, and not been able to get pregnant during that time? |
| New York University Women's Health Study (NYU)c | USA | 1985–1990 | 128 | 340 | 39–89 | Birth year, cohort entry | 13% | Have you ever tried to get pregnant for ⩾2 years, and during this time not become pregnant? |
| Polish Endometrial Cancer Study (PECS) | Poland | 2000–2003 | 551 | 1925 | 24–75 | Age (±5 years), site | 13% | Have you ever tried to become pregnant for two straight years or more, and during that time, not become pregnant? |
| Patient Epidemiologic Data System (PEDS) | USA | 1982–1998 | 541 | 541 | 26–94 | Age (±5 years) | 13% | Have you ever had difficulty getting pregnant? Did this problem last for >1 year? |
| Shanghai Endometrial Cancer Study (SECS) | China | 1997–2004 | 1199 | 1212 | 30–69 | Age (±5 years) | 5% | If you have never been pregnant, the reason is: (includes your husband is infertile, you are infertile) |
| Turin Case-Control Study (TURIN) | Italy | 1998–1999 | 297 | 307 | 40–75 | None | 8% | Did you ask for a doctor visit because of difficulty in becoming pregnant? |
| US Endometrial Cancer Study (US) | USA | 1987–1990 | 433 | 320 | 25–78 | Age (±5 years), race, telephone exchange | 15% | Have you ever tried to become pregnant for 2 straight years or more, and during that time, not become pregnant? |
| USC LA Case-Control Study (USC) | USA | 1987–1993 | 833 | 791 | 50–74 | Age (±5 years) | 60% | Did you not get pregnant for 7 or months while trying to get pregnant or while sexually active and making no effort to avoid getting pregnant? |
|
Cohort | ||||||||
| Iowa Women Health Study (IWHS) | USA | 1986–2007 | 553 | 2212 | 55–90 | Birth year, cohort entry, race, area | 18% | Did you ever try for 1 straight year or more to become pregnant and during that time not become pregnant? |
| Women's Lifestyle Health Study (WLHS) | Sweden | 1991–2011 | 163 | 649 | 31–66 | Birth year, cohort entry | 19% | Clinical data from population-based national registries |
| Pooled studies | — | — | 8153 | 11 713 | — | — | 22% | |
Abbreviation: E2C2=Epidemiology of Endometrial Cancer Consortium.
a
Age at diagnosis for cases and at reference date for controls.
b
Study-specific infertility definition.
c
Cohort study with infertility data collected in case-control interviews.