"He politely told me I was overweight and it might help to lose it."
In one year, Mackenzie lost 3st 9lbs and found out she was pregnant on Boxing Day 2015.
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Liverpool Echo
Sarah Mackenzie is 20 weeks pregnant with her second child
Mackenzie, who is now 20 weeks pregnant, said she immediately joined Slimming World after the suggestion from her GP.
At the time, she weighed 13st 7lbs, which she was told was "too much" for her height of 5ft 3in.
The mother, who was studying Law at university, said she was "shocked" she weighed so much, having always been around 10 stone.
"Because Connor is autistic I couldn't study until he had gone to bed, which was often not until 11.30pm or later, because he switched my laptop off and took my text books," Mackenzie said.
"Sugary drinks and food, and energy drinks, were the only things keeping me awake to do what I had to do."
Mackenzie said she would sometimes skip breakfast and lunch, and have an unhealthy evening meal.
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Liverpool Echo
Sarah Mackenzie before she lost more than three stone
After the warning from her doctor, Mackenzie changed her diet and made sure she ate three healthy meals a day.
For breakfast, she had fruit with yoghurt. At lunch she always opted for brown bread for her sandwiches and for dinner she had chicken with vegetables or fish and rice.
Mackenzie also started exercising by running, and completed the 5k Race for Life, 3k Colour Run and 10k Commando Run throughout the year.
She also began swimming, which she enjoyed with her son.
In 12 months, the mother dropped 3st 9lbs and she credits her weight loss for allowing her to fall pregnant.
"Once I’ve had my baby and got my family, I am going to stay healthy for them."
According to the NHS, being underweight or overweight can lower your chances of conceiving.
Women who are underweight or overweight ovulate (release an egg) less regularly, or sometimes not at all, compared to women of a healthy weight.
Women with a body mass index (BMI) above 30 are likely to take longer to conceive, and GPs may recommend that they lose weight if they are planning to have a baby.
In January 2016, personal trainer Joe Wicks known as The Body Coach claimed his latest weight loss plan helped two women, who were struggling to conceive, fall pregnant.
Wicks, who is most known for his #LeanIn15 video meals on Instagram, said it was his 90-day, Shape, Shift and Sustain (SSS) programme focusing on fat loss that helped the women conceive.
"She did the plan and basically fell pregnant. She came over crying because she was so emotional and happy."
Pregnancy worries and words of comfort
I have no morning sickness! Is that bad news?(01 of10)
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You might have read things about how morning sickness signifies a healthy level of pregnancy hormones – but not having morning sickness does not mean you're lacking! Although many women suffer with it (and 'suffer' really is the word), many other women do not. Some women have it one pregnancy, but not in another. Attend all your usual checks and count yourself as one of the lucky ones! (credit:Alamy )
I drank before I knew I was pregnant, I might have harmed the baby(02 of10)
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This happens to many, many expectant mums, and it's unlikely to be a cause for concern at all. Mention it to your GP/midwife, and just keep off the booze now, until you can enjoy a celebratory glass of fizz when your bundle arrives. (credit:Alamy )
I'll lose the baby(03 of10)
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It's estimated about one in five pregnancies ends in early miscarriage, and it's thought most of those occur simply because the foetus wasn't developing properly. It does happen, but don't let it rule your thoughts because the vast majority of pregnancies do succeed. Try not to worry and remember that once you're into the second trimester, the chances of miscarriage is dramatically reduced. (credit:Alamy )
My baby might not be 'perfect'(04 of10)
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It's estimated that one in 16 babies in the UK is born with a birth defect – but this figure refers to all birth defects, and many are mild and can be treated. So it's likely your baby won't have a birth defect, and even if they do, they will be perfect in their own way – remember support is available for every eventuality. Take your folic acid and attend your antenatal screening appointments. (credit:Alamy )
I won't make it to the hospital on time(05 of10)
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You might have read terrifying stories about pregnant women giving birth in car parks and taxis – but these stories make it to the news because they are extraordinary, in the literal sense of the word! It very rarely happens, and most women get plenty of warning that labour is beginning. So plan well, and all is very likely to be fine. (credit:Alamy )
I might have to have a c-section(06 of10)
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If you do end up needing a c-section, you might feel disappointed – but believe us, in the moment the only thing you'll really care about is the safe delivery of your baby. It won't be the end of the world and you won't care a jot when your baby is in your arms. (credit:Alamy )
I won't be able to cope during labour(07 of10)
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There is just no telling how labour will be for you, so don't worry about it now. Make your birth plan, discuss it with your partner and midwife, and go with the flow on the day (it's okay to change your mind!). There will be lots and lots of help and support at your disposal. Not to mention drugs, should you need them. (credit:Alamy )
Labour will humiliating (will I poo on the bed?!)(08 of10)
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You've heard about that then? It can happen, but the doctors and midwives have seen it all – they have experienced every possible scenario. They won't be worrying about things like that, so neither should you. (credit:Alamy )
I don't know how to be a mum(09 of10)
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No-one does until they become one! Every new mum feels like they're winging it in the early days. As your baby grows and you get to know them, you'll learn. Trust in the fact that just about every mother has gone through it… and survived. (credit:Alamy )
I'm worried about gaining all that weight(10 of10)
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You will put on weight, yes – but it's normal and nothing to be afraid of! Much weight gain is actually down to the baby, the placenta, extra blood in your system and the retention of water. Pregnancy changes your body in myriad ways – just enjoy it, and let your body just do its thing at this special time. Remember, there's no need to 'eat for two'… but eat what you need and don't count calories. (credit:Alamy )