Hormonal
The association between underweight status (BMI <20) and fecundability is conditional on parity: it is associated with reduced fecundability in nulliparous women but increased fecundability in parous women.
If you are underweight (BMI <20), your fertility status depends on your history. If you have never had children, being underweight may make it harder to conceive. However, if you have had children before, being underweight might actually be associated with a higher chance of conceiving in each cycle.
Underweight was associated with reduced fecundability among nulliparous women (FR = 0.82, 95% CI = 0.63 –1.06) and increased fecundability among parous women (FR = 1.61, 95% CI = 1.08 –2.39).
Why this rating
The finding is based on stratified analysis, and the confidence interval for nulliparous women includes 1.0 (barely), suggesting weaker evidence for the negative effect in that group.
Source
An internet-based prospective study of body size and time-to-pregnancy
Lauren A. Wise et al. · Human Reproduction · 2009
DOI 10.1093/humrep/dep360
More from this paper
- Female overweight (BMI 25-29), obesity (BMI 30-34), and very obesity (BMI >=35) are associated with significantly reduced fecundability (longer time-to-pregnancy) compared to normal weight women, with the association strengthening when central adiposity (waist circumference) is controlled for.Good
- Weight gain of 15 kg or more since age 17 is associated with reduced fecundability (longer time-to-pregnancy), independent of current BMI at age 17.Good
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