What does this research mean for the field?

Maternal BMI has a non-linear, context-dependent association with cumulative intrauterine insemination (IUI) success, where live birth probability increases up to a BMI of approximately 21.2 kg/m² and plateaus or declines thereafter depending on basal FSH levels and treatment protocols. Novelty: ClaimNovelty.INCREMENTAL. Consensus alignment: ConsensusAlignment.NEUTRAL.

What question did this study set out to answer?

This study evaluates the independent and non-linear relationship between maternal BMI and cumulative live birth rates in women undergoing intrauterine insemination.

June 6, 2026Open Access

Non-linear and context-dependent association of maternal BMI with cumulative live birth in Chinese women undergoing intrauterine insemination: a retrospective study of 3788 cycles

Key Points

This study evaluates the independent and non-linear relationship between maternal BMI and cumulative live birth rates in women undergoing intrauterine insemination.
Retrospective analysis of data from 1951 couples across 3788 cycles.
Used multivariable generalized linear models, generalized estimating equations, and Cox proportional hazards models for analysis.
Generalized additive model and two-piecewise linear regression characterized non-linear patterns and thresholds.
No significant association between maternal BMI and clinical pregnancy or live birth in the first cycle (all P > 0.05).
Per-cycle analysis showed modest positive correlations for pregnancy (aOR 1.04, P = 0.004) and live birth (aOR 1.03, P = 0.030).
Cumulative success showed a non-linear pattern with increased live birth probability up to a BMI of approximately 21.2 kg/m² (aHR: 1.12, P = 0.007) before plateauing.

Abstract

Background Evidence regarding maternal body mass index (BMI) and intrauterine insemination (IUI) outcomes remains controversial. This study aimed to evaluate such independent associations, focusing on potential non-linear patterns, clinical thresholds, and population-specific heterogeneities. Methods Data from 1951 couples (3788 cycles) were retrospectively analyzed. Multivariable generalized linear models (GLM), generalized estimating equations (GEE), and Cox proportional hazards models assessed first-cycle, per-cycle, and cumulative success, respectively; generalized additive model (GAM) and two-piecewise linear regression characterized non-linear patterns and thresholds. Results While maternal BMI showed no significant independent association with clinical pregnancy or live birth in the first cycle (all P 0.05), per-cycle analysis of 3788 cycles revealed a modest positive correlation (pregnancy: aOR 1.04, P = 0.004; live birth: aOR 1.03, P = 0.030). Notably, cumulative success followed a non-linear pattern ( P LRT = 0.027), with live birth probability increasing until a BMI of approximately 21.2 kg/m² (aHR: 1.12, P = 0.007) but plateauing thereafter, potentially linked in part to an exploratory observation of higher spontaneous abortion rates in the obesity group (29.03%, P = 0.087). Subgroup analyses suggested potential heterogeneities in these associations across basal FSH levels and treatment protocols used in the first cycle ( P interaction = 0.030 and 0.009, respectively). Specifically, for the FSH 8mIU/mL group, a non-linear association was suggested ( P LRT = 0.020), with success increasing up to approximately 21.2 kg/m² (aHR: 1.12, P = 0.011) and plateauing thereafter. Similarly, for patients whose first cycle used a gonadotropin protocol, a potential reversal was observed beyond approximately 21.0 kg/m² ( P LRT = 0.020), where the trend shifted to a significant decline (aHR: 0.81, P = 0.023). Conclusions Maternal BMI appears to exhibit a non-linear, context-dependent association with cumulative IUI success, underscoring the potential need for individualized preconception management.

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