The greatest risk is among those whose body mass index (BMI) falls by five points or more between pregnancies, researchers have discovered.
By far the healthiest option - for mother and baby - is for the woman to get back to her weight before she first became pregnant.
However, researchers warn mothers who keep on the pounds between pregnancies that they greatly increase their chances of complications second time around.
Even an increase of just one or two extra units on the BMI scale significantly increases the risk of pre-eclampsia, diabetes, and hypertension with the second pregnancy. A weight gain of more than three on the BMI scale heightens the chances of a stillbirth.
(Source: British Medical Journal, 2007; 335: 169).