Incidence and risk factors of infertility among couples who desire a first and second child in Shanghai, China: a facility-based prospective cohort study

BACKGROUND: With the implementation of the two-child policy in China, more couples have expressed the desire to have another child. We conducted this study to evaluate the incidence of infertility and risk factors in couples intending to have a first and second child. METHODS: From 2013 to 2017, a prospective cohort study was conducted at the pre-pregnancy center of the International Peace Maternal and Child Health Hospital. The participants were selected by screening and random sampling couples who came to the pre-pregnancy center. Data regarding patient sociodemographic characteristics, reproductive and gynecological history, male disease history, and laboratory and imaging examination results were collected. Couples were followed up every 3 months until pregnancy or for 12 months, whichever came first. Multi-factor logistic regression was used to analyze risk factors for infertility. Adjusted odds ratios (aORs) and corresponding 95% confidence intervals (CIs) were calculated and adjusted for potential confounding factors. RESULTS: The overall infertility incidence was 16.95% (369/2177). The infertility incidence of “first child intention” and “second child intention” was 19.30% (355/1839) and 4.14% (14/338), respectively. This study found great differences in both infertility rate (P < 0.001) and risk factors between the two groups. Risk factors for “first child intention” infertility included advanced age (> 35 years) (aOR = 1.70, 95% CI 1.27–2.28), abnormal body mass index (BMI) (aOR = 1.58, 95% CI 1.31–6.26), longer menstrual periods (aOR = 4.47, 95% CI 2.25–8.88), endometrial polyps (aOR = 2.52, 95% CI 1.28–4.97), polycystic ovarian syndrome (PCOS) (aOR = 6.72, 95% CI 1.79–7.39), salpingostomy (aOR = 3.44, 95% CI 1.68–7.07), and history of mycoplasma (aOR = 1.54, 95% CI 1.09–2.40). However, in the “second child intention” group, clinical risk factors slightly differed and included leiomyoma (aOR = 5.60, 95% CI 1.06–29.76), and higher age (> 40 years) (aOR = 7.36, 95% CI 1.01–53.84). CONCLUSION: The overall infertility rate in Shanghai is similar to that of other large cities in China. Marriage at advanced ages has become increasingly common. As such, the government must consider subsidies to encourage childbirth at childbearing ages, which can improve fertility levels. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s12978-022-01459-x.