See BBC News article. It is such a shame that overweight people are mostly unaware - because the health professionals do not tell them - that reducing their intake of salt and salty food will reduce their excess weight by reducing their excess fluid retention/water weight, caused by sensitivity to salt. It is even more important, during pregnancy, that women keep their salt/sodium intake low, because the natural hormone changes that occur during pregnancy make them even more vulnerable to salt during the period of pregnancy. It is salt reduction, rather than calorie reduction, that should be advocated. Salt reduction would reduce the risk of miscarriage, as well as the risk of high blood pressure, pre-eclampsia, excessive weight gain and many other health problems associated with pregnancy, both IVF pregnancies and non-IVF pregnancies.
See Pregnancy Advice.