Introduction: The impact of early pregnancy complications on completed family size is unknown. Here, we hypothesize that early pregnancy complications and adverse outcomes may influence family size. Material and methods: In this nationwide, registry-based study we included all 458 475 women born 1957–1972 who lived in Denmark from age 20–45 years with at least one registered pregnancy. The main outcome of the study was number of children per woman by age 45, estimated using a Generalized Linear Mixed Model. Exposures were: (a) total number of pregnancy losses experienced (0, 1, 2, ≥3); (b) highest number of consecutive pregnancy losses (0, 1, 2, ≥3); (c) sex of firstborn child; (d) outcome of first pregnancy (live birth, stillbirth, pregnancy loss, ectopic pregnancy, or molar pregnancy). Results: Number of live births was negatively influenced by maternal age and adverse first pregnancy outcomes, especially ectopic pregnancies. A 30-year-old woman with a first ectopic pregnancy was expected to have 1.16 children (95% CI 1.11–1.22) compared with 1.95 children (95% CI 1.86–2.03) with a first live birth. Three or more consecutive losses also decreased number of live births significantly: 1.57 (95% CI 1.50–1.65) compared with 1.92 (95% CI 1.84–2.0) with only live births. The total number of pregnancy losses had no effect before the age of 35 years. Sex of firstborn had no effect. Conclusions: Previous pregnancy history has a significant effect on number of children per woman, which is important at both individual and societal levels. Pathophysiological research of adverse pregnancy outcomes should be an urgent priority as the causes remain poorly understood.