Weight gain during pregnancy: What’s best for baby and for Mum?

Discovering there’s a new baby on the way is a time of great excitement. However, the excitement is likely to be accompanied by some apprehension about juggling work, relationships, finances and households. Weight gain during pregnancy is often overlooked in our pregnancy planning, yet it essential for maximising the health of mum and baby. Gaining too much or too little weight during pregnancy can increase complications during pregnancy, labour and childbirth. Research shows that nourishment of the baby during pregnancy not only impacts on the health of that baby throughout infancy and childhood, but also throughout adolescence and into adulthood.

First things first: A healthy weight before pregnancy

A healthy weight prior to conception assists with fertility and also reduces complications during pregnancy, labour and childbirth. Once pregnant, women with a higher body mass index (BMI) are more likely to have complications, including gestational diabetes, blood pressure disorders (including pre-eclampsia), prolonged labour and delivery, increased intervention (induction, assisted delivery, caesarean deliveries) and large for gestational age (LGA) babies. Babies born to overweight or very overweight mothers have an increased risk of childhood obesity and long-term health problems. Women with low BMIs are more likely to have premature and small for gestational age (SGA) babies.

If you are underweight or overweight (above or below BMI 19-25) and trying to conceive, a dietitian can work with you to support you in making changes to achieve a healthy weight to increase your chance of conceiving and having a healthy baby.

Why does weight gain during pregnancy matter?

Weight gain during pregnancy affects the growth of the baby. Women who gain too much weight during pregnancy are more likely to have a baby that is too large for gestational age (LGA*). Women who gain too little weight during pregnancy are more likely to have a baby that is too small for gestational age (SGA**).

There are risks for both LGA and SGA infants.

Babies that are LGA are often more difficult to deliver and are associated with more prolonged delivery time, difficult birth and birth injury. Babies that are LGA are also more likely to be overweight or obese as children and adults.

Babies that are SGA are more likely to have complications at birth including decreased oxygen levels, low blood sugar levels, too many red blood cells and difficulty maintaining normal body temperature. During infancy, SGA babies are at higher risk of failure to grow, slow cognitive development and chronic diseases in adulthood.

Both LGA and SGA babies are more likely to be delivered by Caesarean section.

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*LGA: Large-for-gestational age

LGA is a term used to describe babies who are born weighing more than the usual amount for the number of weeks of pregnancy. LGA babies have birthweights greater than the 90th percentile for their gestational age, meaning that they weigh more than 90 percent of all babies of the same gestational age.

**SGA: Small-for-gestational age

SGA is a term used to describe babies who are born weighing less than the usual amount for the number of weeks of pregnancy. SGA babies have birthweights less than the 10th percentile for their gestational age, meaning that they smaller than 90% of babies for birthweight at the same gestational age.

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Monitoring the baby’s growth during pregnancy

Growth of the baby is one of the key measurements used to reflect the intrauterine environment to which the baby was exposed. During pregnancy, a baby’s growth can be measured and birthweight can be estimated. One way of doing this is by measuring the height of the fundus (the top of a mother’s uterus) from the pubic bone. This measurement, in centimetres, usually corresponds with the number of weeks of pregnancy. If the measurement is high for the number of weeks, the baby may be larger than expected. If the measurement is low for the number of weeks, the baby is likely to be smaller.

Small and large babies may reflect a normal physiological variance and genetics plays a part, however, the growth of the baby is strongly influenced by the mother’s weight gain during pregnancy and appropriate weight gain reduces the risk of having an LGA or SGA baby.

So how much weight should be gained during pregnancy to maximise the health of mother and baby?

The amount of weight gain recommended during pregnancy is based on the mother’s BMI before pregnancy. You can calculate BMI by using the calculator on the Get Healthy website (http://www.gethealthynsw.com.au/healthier-you/tools-and-calculators/bmi-calculator/).

If your pre-pregnancy BMI was…	The recommended weight gain during pregnancy is…
Less than 18.5 kg/m²	12.5 to 18kg
18.5 to 24.9 kg/m²	11.5 to 16kg
25 to 29.9 kg/m²	7 to 11.5kg
Above 30 kg/m²	5 to 9kg

Should weight gain be different in each trimester?

First Trimester: Women can expect to gain 2-3 kg in the first 3 months of pregnancy.

Second and Third Trimesters:

If your pre-pregnancy BMI was…	The recommended rate of weight gain is…
Less than 18.5kg/m²	0.5kg per week
18.5 to 24.9 kg/m²	400g per week
Above 25 kg/m²	Less than 300g per week

How much extra food is needed for healthy weight gain?

The table below provides an example of the extra food needed for healthy weight gain in women whose pre pregnancy BMI is in the healthy weight range (18.5 to 24.9). Women with a BMI below 18.5 need slightly more food than shown above and women with a BMI over 24.9 needs less food than shown above to support healthy weight gain during pregnancy.

Trimester	Calorie Intake	Extra food equivalent
1st Trimester	0	N/A
2nd Trimester	330 cals/1380kJ	200g yoghurt + 50g red meat
3rd Trimester	400 cals/1670kJ	200g yoghurt + 50g red meat + 1 slice multigrain grain

Healthy eating during pregnancy

A healthy pattern of weight gain during pregnancy is vital for the health of mum and baby. Dietary intake determines weight gain as well as maintaining health and supporting the growth and development of the baby. Pregnant women need to consume a variety of foods to ensure that the baby receives a sufficient amount of nutrients, while supporting healthy weight gain. If you are pregnant or planning a pregnancy, speak with an Accredited Practising Dietitian.

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