Weight gain during pregnancy goes with the territory because you are growing another human (or more than one) and this is partly made up of;
- baby on average weighs about 7lb (3.2kg)
- a placenta weighs approximately 1.2lb
- 600-800ml amniotic fluid (your waters) at term so approximately 1.7lb (0.8kg)
- 5L extra blood volume at term weighing approximately 3.5lb
So, in short without even gaining an additional pound of fat you can expect to gain around one stone (14lb or 6.35kg) just from growing your baby!
The NHS advises that an average woman should be gaining between 22-28lbs over the course of a full-term pregnancy, however, this is a guideline and if you have any concerns about your weight you should discuss this with your Midwife.
Why do we talk about weight during pregnancy?
At the start of your pregnancy, you will be invited to meet a Midwife for a “Booking” appointment:
- you will decide where you wish to birth your baby,
- your Midwife will take a comprehensive history from you about any previous pregnancies,
- your physical and mental health,
- any medications you may be taking,
- family health history,
- details of your partner if you have one,
- your pregnancy risk factors will be assessed,
- your booking bloods will be taken if you consent,
- blood pressure, urine test and height, weight and BMI will be calculated.
The reason we advise taking weight and height measurements is so that we are able to calculate your BMI. This is then presented as a number which is a measurement of body fat and categorises you as:
- <18.5 Underweight
- 5 – 25 Health Weight
- 1 – 29.9 Overweight
- > 30 Obese
The majority of women with a raised BMI will go on to have a normal pregnancy and a safe labour and birth, however, BMIs that are out of the Healthy Weight range are associated with increased risks during pregnancy, labour, birth and the postnatal period including:
- Thrombosis (blood clots)
- Gestational Diabetes
- Raised Blood Pressure and Pre-eclampsia
- Miscarriage/Preterm Labour/Stillbirth
- Induction of Labour
- Shoulder Dystocia
- Anaesthetic Complications
- Postpartum Haemorrhage
- Wound Infections
What can I do to reduce my risks of pregnancy complications?
If your BMI at booking is 30 or higher you will be advised to take a higher dose (5mg) of Folic Acid because your risk of baby developing a Neural Tube Defect such as Spina Bifida increases significantly. You will also be offered Consultant-led care where you may see a Consultant at some of your appointments so you and baby can be monitored to ensure your wellbeing. You will also be offered an Oral Glucose Tolerance Test (OGTT) to check if you have developed Gestational Diabetes, this usually takes place around 24 weeks gestation. You may be offered Low-Molecular Weight Heparin (LMWH) which is a daily injection to thin your blood and reduce your risk of developing blood clots (VTE).
Additionally, if your BMI is over 35 and you have any other risk factors for pre-eclampsia you will also be offered a prescription for aspirin (75-150mg daily). You will also be offered serial growth ultrasound scans to monitor the development of your baby as measuring your abdomen using a tape measure may be less accurate.
And, if your BMI is over 40 in addition to all of the above you will be advised to have an appointment with an Anaesthetist in the latter stages of your pregnancy to discuss pain relief and surgical options.
If you are at the other end of the BMI scale and are classed as being Underweight (less than 18.5) this can also have complications for you and baby during pregnancy including:
- Miscarriage
- Low Birth weight
- Premature Birth
- Fetal Growth Restriction
At your booking appointment you may be offered a dietician referral to support you to gain weight healthily during your pregnancy and additional growth ultrasound scans to monitor your baby’s development.
If you do have a raised BMI at your booking appointment you should not aim to lose weight during your pregnancy instead you may be offered, or you can request, a referral to a dietician for advice about healthy eating, and it is important to begin some low-impact activity such as walking or swimming for 30 plus minutes 3-5 times a week, sufficiently to raise your heart rate slightly but to still be able to hold a conversation. the famous philosopher, Hippocrates, once said that “Walking is man’s best medicine”. The Royal College of Midwives (RCM) has endorsed Slimming World as a partner to support women with healthy eating throughout the pre-conception to postnatal continuum so if you are looking for any advice this is a great place to start.
We also have a lot of useful information about healthy eating in pregnancy on our website so take a look at our blog What to eat when pregnant.
