Dr Danie Schneider
Obstetrician and Gynaecologist, Somerset West

Weight gain in pregnancy

Pregnancy is a critical period during which maternal nutrition and lifestyle greatly influence the health of the mother and child. We therefore have a unique opportunity to influence the long term health of both the mother and infant. Modern obstetric care involves recording a woman’s weight, height and BMI early in the pregnancy and we do not weigh women repeatedly during pregnancy as a matter of routine. Weight gain is part of the physiological changes of pregnancy and we only weigh women again if clinical management can be influenced or if nutrition is a concern.

Why do I gain weight in pregnancy?

Physiological changes related to pregnancy result in a weight gain of about 11 kg. Weight gain during pregnancy can be attributed primarily to increases in maternal body water and fat. Most of the weight gain at term is distributed as follows: baby 3.2-3.6 kg, fat stores 2.7 to 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, uterus 0.9 kg and placenta 0.7 kg.

What happens to a woman’s metabolism during normal pregnancy?

Pregnancy is characterized by complex metabolic adaptations that are necessary to ensure a continuous supply of nutrients to the baby. From a metabolic point of view there are two different periods during gestation. In the first half of pregnancy there are maternal changes that lead to the storage of energy and nutrients and an increase in the mother’s lipid/fat stores (anabolic state). Your body therefore has in inbuilt system to store nutrients for later in the pregnancy. Late pregnancy is characterized by a catabolic (breakdown of nutrients) state, allowing greater substrate availability for fetal growth by preserving glucose and amino acids for transfer to the baby. At this stage of your pregnancy your body keeps the nutrients available in your system to accommodate the rapid growth of the baby.

What is healthy weight gain in pregnancy?

It is important to understand that there is no uniform definition of healthy weight gain in pregnancy. A recent worldwide study showed that about 50 % of national guidelines follow the 2009 American Institutes of Medicine (IOM) gestational weight gain guidelines. These guidelines have been drawn up to lower the risk of low birth weight babies and not actually for the prevention of excess weight gain, which is the problem of our modern society.

The IOM guidelines state that for a singleton pregnancy a normal weight woman (BMI 18.5-24.9 kg/m2) should gain 11.5 – 16 kg. If the BMI is under 18.5, then she should gain 12.5-18 kg. For overweight women (BMI 25-29.9) the weight gain should be 7-11.5 kg. For obese woman (BMI >30) the weight gain should be 5-9 kg.

For underweight and normal weight women, the guidelines therefore translate to about 0.5 kg weight gain per week in the second and third trimesters; for overweight and obese women, the guidelines translate to about 0.25 kg weight gain per week in the second and third trimesters.

What are dangers of excessive weight gain?

Studies have shown that excess weight gain has been associated with an increased risk of pregnancy-related hypertension, caesarean delivery, gestational diabetes, childhood overweight or obesity, as well as future adult obesity.

What are the dangers of sub optimal weight gain?

The major concern of gestational weight gain below IOM recommendations is an increased risk for low birth weight as well as preterm birth.

How can I control my weight gain in pregnancy?

If you have a BMI in the normal range then you should follow basic nutritional advice, continue to be physically activity throughout pregnancy and exercise ( see separate guidelines under heading “ exercise in pregnancy” ). It is important to understand that caloric intake does not need to increase in early pregnancy, as weekly weight gain in the first trimester should be minimal. This is obviously good news if you are struggling with morning sickness! You need to gain only about 0.5- 1.8 kg in the first few months and can do this by eating a healthy diet. Later in pregnancy, caloric intake needs to increase by only about 300 calories per day to achieve the 0.5 kg recommended weight gain per week. It is a myth that you “need to eat for two”. The most accurate way to monitor whether you’re getting the appropriate energy intake is to monitor your weight gain.

To help you choose the right amounts to eat during pregnancy, the MyPlate Daily Checklist for moms ( www.choosemyplate.gov ) can be very helpful. They also have a pregnancy weight gain calculator on the web page.

I fell pregnant before I could optimize my weight, now what?

It is important to appreciate that you are not alone! A recent review of more than 1million pregnant women showed that more than 47 % had gestational weight gain more than the IOM guidelines. It is important to note that because pregnancy is the only time in an overweight woman’s life when she is encouraged to gain weight, this can cause much uncertainty and confusion. A consultation with a nutritional specialist /dietician could therefore be of considerable help. It is important not to start dieting in pregnancy, but to follow the above dietary advice and to lose weight after the pregnancy.

Countless examples exist of women who made a mind shift and adopted a healthy lifestyle in pregnancy. It is important not to be sedentary as far as possible. Become active and build physical activity into your daily life by first walking and climbing stairs, rather than sitting for long periods. Build up to 15 minutes walking at a pace where you can still talk comfortably. Follow general exercise guidelines as discussed under the separate heading.

You can further lower your and your baby’s risks by quality antenatal care. It is important to appreciate that most women who are overweight have a straightforward pregnancy and birth and deliver healthy babies. However, being overweight does increase the risk of complications to both you and your baby. We will lower your risks by focusing on monitoring fetal growth, diagnosing diabetes or hypertension, involving an experienced anesthetist for a pre labour assessment if needed and preventing blood clots /thrombosis. Note that if you are overweight and gain less weight than prescribed by the IOM guidelines, we do not encourage extra weight gain as long as the baby is growing appropriately.

What about post-partum weight?

It is estimated that approximately 50% of gestational weight gain is lost in the first six weeks after delivery. There is a slower rate of loss through the first six months. Women who gain more than the IOM guidelines during the pregnancy are twice as likely to retain more than 9 kg weight after delivery. It is therefore important to start with a healthy exercise and meal plan during pregnancy and continue after birth.

It is important to understand that research has shown that gaining about 9 kg between pregnancies leads to an increased risk of pre-eclampsia, diabetes, big babies and caesarean section in the following pregnancy. Changes you make now can lower risks in future pregnancy.

Good news is that diet and exercise facilitate post-partum weight loss and is safe for breastfeeding and non-breastfeeding women. Research has shown that moderate reduction in caloric intake can be well tolerated by breastfeeding women and does not impair the function of your breasts or the growth of your baby. You can breastfeed; exercise and diet at the same time, but should limit caloric restriction and the rate of weight loss. You should not loose weight faster than 0.5 kg per week. Some experts suggest that a return to pre-pregnancy weight by 6 -12 months after birth is a safe guideline. Statistics show that exclusive breastfeeding has the added advantage of helping women avoid long-term postpartum weight gain.

Bottom line

Physiological changes in pregnancy result in weight gain. It is a myth that you need to eat for two. Do not diet during pregnancy. Get professional advice if unsure. Stay active and get regular exercise. Good antenatal care can lower risks for you and your baby.