A study of 104 mums-to-be spotted the signals.
The analysis found that hydrogenated fats, as they are described on food labels, increase the body's resistance to the hormone insulin.
In turn, this boosts the levels of a substance which has been shown to increase the risk of a miscarriage, reports The Sun.
In the study, Dr Charles Glueck and his team in Ohio, US, found that a high intake of the fats - such as by eating junk food daily - proved a danger to the unborn child.
Experts say trans fats should form a maximum of one per cent of an adult's daily calories.