Can obesity affect IVF embryo development even when blood pressure and blood sugar are normal? A study of 3,770 women linked overweight or obesity to lower normal fertilization and high-quality blastocyst formation rates, without clear differences by metabolic health.
It can be tempting to assume that the absence of diabetes or hypertension means body weight has little bearing on IVF. The findings suggest the picture is more complicated.
Researchers at the Reproductive Medicine Centre of Jiangxi Maternal and Child Health Hospital in China reported the study in the Journal of Ovarian Research.
Lower embryo-development measures despite good metabolic health
The team retrospectively analyzed 3,770 women with tubal-factor infertility undergoing their first IVF or intracytoplasmic sperm injection (ICSI) cycle between January 2016 and March 2026.
Participants had normal ovarian reserve, limiting the influence of other infertility causes such as polycystic ovary syndrome or diminished ovarian reserve.
Using blood pressure, glucose and lipid measures, the researchers classified 1,849 women as metabolically healthy and 1,921 as metabolically unhealthy. They compared fertilization, embryo development and pregnancy outcomes by body mass index (BMI).
Overweight or obesity was associated with a 3.4-percentage-point lower normal fertilization rate in conventional IVF. In ICSI, normal fertilization was 3.9 percentage points lower and the proportion of mature oocytes was 4.1 percentage points lower.
In conventional IVF, high-quality blastocyst formation was 3.5 percentage points lower. A blastocyst is an embryo that has developed for approximately five to six days after fertilization, an important stage for deciding which embryos to transfer or freeze.
These associations did not differ significantly by metabolic-health status. Favorable glucose, blood pressure and lipid results did not eliminate the observed weight-related differences.
More eggs does not automatically mean better embryos
Higher BMI was also associated with more oocytes retrieved. An indirect pathway involving follicle-stimulating hormone (FSH) was estimated to explain approximately 4.7–6.3% of that association.
Yet retrieving more eggs does not necessarily yield more high-quality embryos. Egg number, maturity, normal fertilization and blastocyst development measure different aspects of treatment.
The findings support looking beyond the retrieval count when assessing IVF outcomes.
Did the differences translate into fewer live births?
The researchers also examined clinical pregnancy, miscarriage and live birth. After adjustment for multiple comparisons, they did not find statistically significant associations for these outcomes. Absolute differences in clinical pregnancy and live-birth rates were within 2.5 percentage points.
This study therefore cannot establish that obesity reduces IVF live-birth success by a particular amount. More research is needed to determine how differences in fertilization and embryo development translate into pregnancy and birth.
The authors proposed that adiposity itself may be associated with reproductive outcomes apart from metabolic abnormalities. However, the absence of a statistically significant difference by metabolic health does not rule out metabolic influences.
This observational study concerned first treatment cycles in women with tubal-factor infertility and normal ovarian reserve. It cannot be applied equally to all patients, nor does it prove that weight loss will improve embryo quality or live birth.
Normal blood pressure or glucose alone may not exclude weight-related associations. Fertility care needs to consider metabolic health and body weight alongside age, ovarian function and treatment timing.
Study source
Xiaoju Wan, Min Yu, Jun Tan and colleagues, Jiangxi Maternal and Child Health Hospital: “Beyond metabolic comorbidity: metabolic health stratification reveals BMI–ART associations in tubal factor infertility,” Journal of Ovarian Research (2026). DOI: 10.1186/s13048-026-02248-x. PMID: 42860527.
Related reading
For another example of why embryo-development measures need careful interpretation, read about slow embryo development and normal chromosomes.
Illustration created with generative AI (ChatGPT, OpenAI); it does not depict an actual patient.
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