Optimal weight gain for pregnancy needs to reflect the woman's pre-pregnancy weight (22). The guidelines on recommended maternal weight gains are based on large obstetric surveys in non-diabetic women in the United States (23). The maternal weight gain required to minimise the frequency of small-for-gestational-age (SGA) infants is higher for underweight (BMI<19.8 kg/m2) than overweight or obese women, see Table 7.2. As the majority of women with pre-existing Type 2 and GDM are already obese it is important that the dietary advice given does not result in higher post-partum than pre-pregnancy weights.
When the pre-pregnancy BMI is >35 kg/m2, the risk of a SGA infant is low and even when little or no maternal weight gain occurs the risk of a SGA infant does not appear to increase (11). Overweight (BMI 26.1-29 kg/m2) and obese (BMI >29 kg/m2) women are more likely to give birth to a LGA infant than normal weight women and this risk increases with increasing maternal weight gain. The US obstetric recommendation for a minimum 7 kg weight gain for all obese women (23,24) may not be universally appropriate (11,25). Nutritional advice given in pregnancy should include appropriate weight gain targets set in early pregnancy and based on pre-pregnancy weight.
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