Young women with unhealthy levels of fat in their blood before pregnancy are more likely to only have one or no child at all, finds a study explaining the previously observed association between lower fertility and heart disease.

Women with an "unhealthy" blood fat profile of high LDL ('bad') cholesterol, triglycerides, and a high triglyceride to HDL ('good') ratio, as well as low levels of HDL cholesterol, measured years before they conceived, were 20 to 100 per cent more likely to be pregnant only once. High levels of LDL, total cholesterol and obesity were also associated with greater odds of having no children. "Pre-existing poor lipid and metabolic profiles could represent one of the possible linkages between previously observed fertility and later (cardiovascular disease)," said the researchers, including Aleksandra Pirnat from the University of Bergen, Norway.

For the study, published in the journal BMJ Open, the team analysed blood samples from 4,322 women, aged 20 and above, which included 1677 childless women, 488 one-time mothers, and 2,157 women with two or more children. The analysis showed that childless women and one-time mothers tended to be overweight and older. They were also found to smoke more than women who had had two or more kids.

Further, one-time mothers also had a higher prevalence of diabetes, and were more than twice as likely to have had fertility treatment. When compared with women who had two or more pregnancies, total cholesterol above the clinically recommended level was associated with greater odds of having no children, irrespective of BMI.

However, since this is an observational study, cause cannot be established. Nevertheless, the findings back previous studies, which found that metabolic irregularities among women of normal weight were an independent risk factor for impaired fertility, the researchers noted.