Weight gain in pregnancy

A bit of history… Before the 1970s, severe dietary restriction was a common obstetrical practice; it was believed that excessive weight gain caused a wide range of obstetric problems. In the 1930s, all pregnant women, irrespective of pre-gravid (pre-pregnancy) weight status, were advised to gain 15 pounds (6.8 kg). Yikes!

Luckily things changed when studies started showing that dietary restriction is associated with risk of low birth weight and infant neurological impairment. By the 1970s women were being recommended to gain 9-11kg during pregnancy.

So what actually contributes to maternal weight gain during pregnancy? At term (ie. by the time you deliver):
– Baby: 3.2-3.6 kg
– Fat stores: 2.7-3.6 kg
– Increased blood volume: 1.4-1.8 kg
– Increased fluid volume: 0.9-1.4 kg
– Amniotic fluid: 0.9 kg
– Breast enlargement: 0.45-1.4 kg
– Uterine hypertrophy: 0.9 kg
– Placenta: 0.7 kg

Anything more than this is usually laid down as fat stores. I’m sorry I know you didn’t want to hear that. But if I said your weight gain was due to an amazing large placenta, well, I’d be a liar.

By 2009, the following guidelines for weight gain in pregnancy were adopted by both the Institute of Medicine and the World Health Organisation:

Singleton pregnancy:
– BMI <18.5 kg/m2 (underweight): 12.5-18.0 kg
– BMI 18.5 to 24.9 kg/m2 (normal weight): 11.5-16.0 kg
– BMI 25.0 to 29.9 kg/m2 (overweight): 7.0-11.5 kg
– BMI ≥30.0 kg/m2 (obese): 5 to 9.0 kg

Twin pregnancy (at term):
– BMI <18.5 kg/m2 (underweight): no recommendation due to insufficient data
– BMI 18.5 to 24.9 kg/m2 (normal weight): 16.8-24.5 kg
– BMI 25.0 to 29.9 kg/m2 (overweight): 14.1-22.7 kg
– BMI ≥30.0 kg/m2 (obese): 11.4-19.1 kg

It is also recommended that all women try to be within the normal BMI range when they conceive.

Please remember these are guidelines only; and that they’ve been formulated from studies that have found adverse maternal and child outcomes with extremes of body weight. Also you shouldn’t be weighing yourself too frequently; some doctors only have their patients weighed at follow ups (ie. every few weeks). Of course you may be required to weigh yourself more frequently if you are having complications in your pregnancy, or you are either too light or too heavy going into or during your pregnancy. If in doubt, please ask your doctor.

References
1. George Macones, Susan M Ramin, Vanessa A Barss. Weight gain and loss in pregnancy. UpToDate 2012.
2. Singer JE, Westphal M, Niswander K. Relationship of weight gain during pregnancy to birth weight and infant growth and development in the first year of life. Obstet Gynecol 1968; 31:417.
3. Committee on Maternal Nutrition/Food and Nutrition Board, National Research Council: Maternal Nutrition and the Course of Pregnancy, Washington DC 1970.
4. www.iom.edu/CMS/3788/48191/68004/68230.aspx. (Accessed May 29, 2009).

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