Descriptive data of the study population.

NA = not available, i.e. questions not included in the questionnaire, Q1 = 1st quartile, Q3 = 3rd quartile.
1Not available for pregnancies before 1982.
ASame sex female twin pairs born 1926–1966.
BSame sex female and male twin pairs born 1944–1971.
CEach twin was living together with a partner in a long-term relationship. The adolescent child was 11–22 years old and was living together with the parents. The cousins were the same sex and not more than 4 years apart in age.

NA（Not Available，即问卷未纳入相关问题）；Q1（1st quartile，第一四分位数），Q3（3rd quartile，第三四分位数）。
[1] 1982年之前的妊娠相关数据不可用。
A组：1926–1966年出生的同性女性双生子对。
B组：1944–1971年出生的同性双生子对（含女性双生子对与男性双生子对）。
C组：每对双生子均与长期伴侣共同居住；受试青少年子女年龄为11–22岁，且与父母共同生活；表亲均为同性，且年龄差距不超过4岁。