The science behind a mum bum: How having a baby can alter your posterior in unlikely ways

Almost eight years ago it nearly stole the show at the wedding of the century, and remains a byword for peachiness and perfection. And when Pippa Middleton was photographed recently, out with her baby son, ‘that’ bottom of hers was still attracting attention — but not for the same reasons.

While the Duchess of Cambridge’s 35-year-old younger sister has undoubtedly regained her pre-pregnancy slenderness since giving birth to Arthur five months ago, there’s one significant difference: her bottom appears a little . . . flat.

While the concept of ‘Mum Tum’ is nothing new — we all know the toll having a baby can take on formerly flat abs — who knew our rumps can also bear the brunt of pregnancy?

Last month she was pictured 19 weeks after the birth of her son Arthur

Pippa Middleton nearly stole the show at her sister’s wedding in 2011 (left). And last month, she was pictured (right) 19 weeks after the birth of her son Arthur 

Hormones, posture, weight gain and childbirth all contribute to ‘Mum Bum’, according to experts, and even the best-maintained rears are susceptible.

But what causes it? And will Pippa ever get ‘that’ famous bottom back?

HORMONAL HORROR

Hormones flood through the body when you’re pregnant. Obviously they’re necessary for growing a healthy baby and preparing the body for birth, but there can be side-effects.

During pregnancy you produce a hormone called relaxin, which helps prepare the uterus and cervix for giving birth, and is the main culprit for making the bottom sag.

Produced by the placenta and ovaries, it relaxes ligaments and muscles, but the hormone does not differentiate, and affects the whole body — including the buttocks, although the skin and soft tissues are most affected.

Cheryl attending a premiere at the 69th Cannes Film Festival in 2016

Cheryl on the catwalk of the L'Oreal show at Paris Fashion Week in 2019

Cheryl Tweedy, 35, is now a mum to two-year-old Bear Payne (right), 17 years after the start of career

‘When someone comes to see me, I can tell just by looking at their bottom whether they’ve had children,’ says consultant plastic surgeon Marc Pacifico.

‘Your buttocks, or glutes, are composed of three muscle groups. There is the gluteus maximus, gluteus medius and gluteus minimus. These determine your basic bottom shape.’

They are big muscles, and changes will be immediately noticeable, particularly to a slim woman like Pippa, where the shape is not obscured by overlying fat.

This will not be the final assault on a woman’s rear: plummeting oestrogen levels as she approaches the menopause cause fat distribution to shift from the hips to the stomach, making the bottom appear flatter still.

DON’T BE FLOORED 

The state of your pelvic floor — the muscular base of the abdomen — affects the pertness of your bottom, as the weight of a baby in your uterus puts pressure on this group of muscles.

‘The pelvic floor is strong in women who haven’t had children, but is far less defined and weaker in those who have,’ says consultant obstetrician Clive Spence-Jones at the London Clinic.

Actress Eva Longoria at 70th Cannes Film Festival in 2017

The Desperate Housewives star is now a first-time mum

Actress Eva Longoria (left) is now a first-time mum after having her son last June (right)

‘Around 40 years ago, surgeons used to speak about “flat bottom syndrome” in women who’d had extensive pelvic floor trauma during, or as a result, of delivery,’

Everything needs to be toned for the buttocks to sit higher and not droop, Mr Spence-Jones says. As well as doing pelvic floor exercises to strengthen the muscles (special clenches which feel like the action of stopping the stream of urine), physiotherapy may help.

CHANGES IN FAT

However slim you may be, hormone fluctuation in pregnancy may affect the quality and consistency of your fat stores.

‘During pregnancy you store vital fat reserves, which you need for birth and breast feeding,’ says Mr Spence-Jones.

‘This is called centripetal fat and is formed under the influence of the extra oestrogen produced by the placenta. It’s structurally different to that which is formed by fat cells, and stored around the hips, buttocks, breasts and abdomen.’

All healthy women need to gain weight — and fat — in pregnancy; most put on 22-26lb according to the nhs.uk website.

‘During pregnancy, fat will be exposed to extra oestrogen throughout the body as well as producing its own,’ says Mr Pacifico. ‘This will potentially have an effect on the quality of the fat — meaning it is less firm.’

‘After oestrogen levels drop post-partum, the consistency of body fat will be softer than previously,’ says Mr Spence-Jones. ‘This will return to normal over the next few months.’

Emily Blunt pictured in 2013 at the 70th Golden Globe Awards

The Mary Poppins star has now had two little girls

Emily Blunt, seen in 2013 at the Golden Globe Awards (left), has now had two little girls as well as starring in blockbuster Mary Poppins

THE AGE FACTOR

we all know that age is a massive factor in how the body responds to pregnancy.

‘Good quality muscle and skin tone will contribute to a firm, rounded look,’ says Mr Pacifico. ‘But ageing causes laxity of muscle. As elasticity deteriorates, drooping skin means lack of support.’

‘Every decade we age more quickly, and pregnancy takes its toll,’ he adds. ‘A 20-year-old may go through pregnancy with barely a change, but by your mid-30s, the body responds more.’

SLOW AND STEADY

Losing weight too quickly after giving birth is not advisable if you want to maintain skin and muscle tone. ‘Slow and steady is the best way so the skin can contract slowly back to how it was,’ says Mr Pacifico.

‘If you reduce calorie intake too much and lose weight too quickly, it’s counter-productive,’ says personal trainer Cornel Chin.

‘A very calorie-restricted diet will burn fat and water but then start to consume muscle, too,’ he says.

Model Rosie Huntington-Whiteley

The 31-year-old has had a son with actor Jason Statham

Model Rosie Huntington-Whiteley, 31, now has a son (born in 2017) with actor Jason Statham

POSTURE PLEASE

Anyone who’s staggered around, arch-backed, during the latter stages of pregnancy knows good posture is difficult. ‘As the bump grows, so your centre of gravity shifts,‘ says yoga teacher Clare Maddalena, founder of LushTums pregnancy yoga classes.

She says that women often counterbalance the weight of the bump by thrusting the pelvis forwards, so the gluteus maximus muscle is deactivated. The hip flexor muscles, found at the front of the hip, become overactive and tight and the glutes generally under-active, leading to poor muscle tone.

‘Many of us already have dormant glutes, which need waking up and activating in order to perk up our posteriors, and pregnancy exacerbates this problem.’

Pregnant women often struggle to stand comfortably. ‘You may find that you put weight on one leg then the other, or lock knees. Ideally, to protect your lower back from aches, stand on both feet, hip distance apart, with a micro-bend in the knee and let the bottom drop a little. However, this can mean weaker glutes.’

TARGET AND TONE 

‘Resistance training is the best form of exercise for firming up the bottom,’ says Cornel Chin.

‘Such exercises as squats will firm up the gluteal muscles.

‘You can’t spot-reduce fat,’ he points out. ‘However, you can, target muscle toning.’

Clare Maddalena says: ‘One great exercise, which can be done while pregnant (as long as your doctor or midwife is happy) is getting on all fours, lifting one leg out straight behind you and doing small pulses — ten to 20. Keep the back as flat as possible. Do the other side, then another set.’

If you feel discomfort, especially around the pubic bone, stop.

Another exercise is a chair squat. ‘Stand with your feet hip-width apart and move into a semi squat, as though you’re lowering into a chair. Hover hips at least an inch higher than the knees.’

She points out that yoga (and Pilates) are both excellent for engaging the muscles in the abdomen, which also helps improve posture and to engage the glutes.

‘Remember that your body is post-natal for up to two years,’ she adds. ‘It takes quite a long time to get back to normal — don’t put too much pressure on yourself.

Rachel Weisz, pictured with Daniel Craig

She gave birth to their child last year aged 48

Rachel Weisz, pictured with Daniel Craig (left), gave birth to their child last year aged 48   

WALK BACK TO FITNESS

No one is saying new mothers ought to be pounding the pavements. ‘There is plenty of time to regain muscle tone, and it’s far more important that you rest when you can,’ says Mr Spence-Jones. But gentle exercise is a good idea, he adds.

Studies have shown that hours spent sitting, resting your weight on your bottom, means that fat cells thrive. Standing up literally takes the weight off them, as well as benefiting circulation and posture. Researchers also say if you sit down for longer, you are more likely to store fat in your bottom.

FEED YOUR MUSCLES

‘It’s impossible to control the bottom shape via diet and weight loss alone,’ says registered nutritionist Rob Hobson.

‘What you want to do is maintain muscle mass, improve skin tone and keep blood sugar levels stable so that you have enough energy,’ he says.

He emphasises the importance of losing weight steadily rather than trying to drop it as swiftly as possible.

‘There is a terrifying trend for women to go on faddish diets,’ he says. ‘Keep it simple and full of protein and fibre; oily fish, chicken breasts, nuts, seeds, wholegrain carbs and masses of vegetables, as well as three good meals a day.’

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