Weight gain during pregnancy is specific to each woman and depends on several parameters. If there is no real rule about it, excessive weight gain can be dangerous for the health of the mother-to-be and her child by causing high blood pressure or gestational diabetes.

There is no ideal weight gain but a recommended range to avoid complications. These recommendations depend on the mother’s BMI (body mass index: weight in kg / height in m2) before pregnancy.

Recommended weight gain based on BMI according to the Institute of Medicine (IOM) (1)

This weight gain does not follow a regular curve. It is generally 500 g / month in the first trimester, then 1 kg / month in the second and 2 kg / month in the third trimester (2). Some expectant mothers may even lose weight in the first trimester due to severe nausea and vomiting.

Apart from the BMI, many other factors influence the weight gain of the expectant mother: genetic factors, age, possible health problems, socio-economic conditions, level of education, family and cultural background, attitude towards weight gain, etc.

The weight of the pregnant woman is closely monitored with a monthly weighing because excessive weight gain exposes the mother-to-be and her baby to various complications:

• hypertension, more common in expectant mothers who have gained more than 18 kg (3)
• induction of labor, more frequent in the event of weight gain greater than 18 kg (4)
• longer labor: the second phase of labor (cervical dilation) is longer in women who have gained more than 18 kg (5)
• more frequent use of instrumental extraction (forceps, suction cups) or cesarean section (6)
• gestational diabetes
• a macrosomia (“big baby”) which can cause various complications during childbirth (shoulder dystocia in particular)

Excessive weight gain during pregnancy exposes the mother to persistent overweight after pregnancy. In addition, several studies (7) (8) suggest a link between high weight gain during pregnancy and excess weight in children.

Weight distribution during pregnancy (9)

Childbirth causes the loss of a few pounds: those of the baby, the placenta, amniotic fluid and other fluids of pregnancy. Thus, it is not uncommon to have shed 6-8 kilos as soon as you leave the maternity ward. In the 10 days following childbirth, the body “deflates”, especially if the mother-to-be suffered from water retention. However, it takes two months for the uterus to return to its normal size and weight.

After these pounds lost naturally, there are often other “pregnancy pounds” that many expectant mothers want to lose quickly. However, specialists recommend moderate weight loss (no more than 2 to 3 kg per month) with a balanced diet. Before returning to sport, rehabilitation of the perineum and the abdominal strap is essential. It is prescribed during the post-natal visit (4 to 8 weeks after childbirth).

Regarding the effects of breastfeeding on post-pregnancy weight loss, the energy cost of breastfeeding leads, in theory at least, to weight loss with a dose-response effect between the degree of breastfeeding and this loss. The difference in weight loss between breastfeeding and non-breastfeeding mothers is most evident between 3 and 6 months, but this difference remains modest (10). A study (11) thus estimated the average weight loss during breastfeeding at 0,2 to 0,8 kg the first six months, and 0,1 to 0,2 kg the following 6 months. Ultimately, 12 months after childbirth, the difference in weight loss between breastfeeding and non-breastfeeding mothers is approximately 0,6 to 2 kg (12).