Findings might explain previously observed link between lower fertility and heart disease, say researchers
The findings might explain the previously observed association between lower fertility and heart disease, suggest the Norwegian researchers.
Several studies have found higher rates of heart disease/stroke among women who have had only one or no children, say the researchers.
But it’s not clear if lower fertility and cardiovascular disease share certain biological factors in common that could help explain this association or whether one-time mums and childless women have a higher cardiovascular disease risk to begin with.
To try and tease this out further, the researchers looked at the potential impact of high cholesterol, triglycerides, and the ratio between the two types of blood fats before conception on the number of subsequent births.
They drew on national birth (MBRN) and health (CONOR) data, which included blood samples taken from women aged 20 and above living in several different regions of the country between 1994 and 2003, and information on lifestyle factors.
Some 4322 women were included in the final analysis: 1677 childless women; 488 one-time mums; and 2157 women with two or more children. One-time mums were defined as those who had had no further births six years after their first pregnancy.
Childless women and one-time mums had more potentially influential risk factors in that they tended to be older (34+), heavier (higher BMI), and to smoke more than women who had had two or more kids.
One-time mums also had fewer years of education, a higher prevalence of diabetes, and were more than twice as likely to have had fertility treatment.
Nevertheless, analysis of the data revealed an association between blood fat profile before pregnancy and the number of subsequent births.
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 percent more likely to be pregnant only once.
High levels of LDL and total cholesterol were also associated with greater odds of having no children, as were overweight and obesity.
But compared with women who had had two or more pregnancies, total cholesterol above the clinically recommended level was associated with greater odds of having no children, irrespective of BMI.
This is an observational study, so cannot establish cause, added to which the blood samples weren’t taken after fasting, nor was there any information on chemical markers known to compromise women’s fertility, all of which might have influenced the findings.
Nevertheless, their findings back previous studies, which found that metabolic irregularities among women of normal weight were an independent risk factor for impaired fertility, say the researchers.
And they conclude: “Pre-existing poor lipid and metabolic profiles could represent one of the possible linkages between previously observed fertility and later [cardiovascular disease].”