Just like babies, bumps come in all shapes and sizes. Yours may be nice and neat like a watermelon, or so large, you feel like a beached whale in maternity pants. The fact is, there's no perfect size for your bump. And size is no indication of your baby's weight, either.
‘Mums-to-be are forever comparing bumps,' says midwife Lorna Bird. ‘But everyone's individual and just because someone has a big bump, it doesn't mean they'll necessarily have a big baby.
‘Bump size and shape depend on various things. With your first baby, you tend to have a neat bump as the stomach muscles are tight. But the more children you have, the more lax your muscles become. Your bump may be more spread out or bigger because the muscles aren't holding in the baby so well.
‘Bump size also depends on how many babies are in there, how much fluid you've got inside and the way your baby is lying. It might also depend on your stature and posture. If you're very slim and upright, for example, you might not have a big bump but you might have a big baby as there's more room for your baby to hide.'
Has your bump made an appearance yet? Read our article all about how early your bump will start to show
Your midwife is the most important person assessing your bump size as she is experienced in knowing whether your baby is the right size.
At each of your antenatal checks, she'll assess you by sight while you're standing up, then feel your bump while you're lying down. Lorna explains, ‘I'll start at the top of the bump, just under the breastbone. I then move down until I reach the top of the womb, called the fundus. Then I'll measure from the pubic bone to the fundus. The number of weeks pregnant you are should roughly correspond to the number of centimetres, so if you're 28 weeks, the measurement should be around 28cm.'
From about 28 weeks, your midwife will be looking to find out exactly which position your baby is lying in. He could be lying with either his head or his bottom down - known as the breech position - although babies can change their position up to 36 weeks, and sometimes even during labour. Or he could be lying sideways, which can make your bump look very wide.
There are several reasons why your bump size might be a cause for concern, but thankfully these are fairly rare. ‘If the bump is particularly small, it might be that the baby isn't growing,' says Lorna. ‘If it's particularly big, we'd look for signs of pregnancy-related diabetes. Or it could be that the mum is carrying a lot of fluid, which can be a sign of a problem.'
If your midwife has any worries, she'll refer you to a consultant clinic or arrange for an ultrasound scan to check that your baby's growth is normal.
5 things that can affect bump size
A Big bump...
...a lot of fluid. Too much amniotic fluid could make your bump seem large. It often occurs with diabetes and identical twins, and sometimes with congenital abnormalities. It can also affect how your baby is lying in the run-up to the birth.
Diabetes Gestational - or pregnancy - diabetes is when the pancreas doesn't produce enough insulin to cope with the amount of sugar in your body. If your sugar levels become too high, sugar crosses the placenta and your baby converts it into fat, muscle and, sometimes, enlarged organs. Diabetes in pregnancy is detected with urine and blood tests and can be controlled with diet, although some women need to inject themselves with insulin. It often leads to mums having big babies. This can affect the type and place of delivery, plus the baby's care in the first few days of life.
A small bump...
...lack of fluid. This makes your bump appear small and can be associated with the baby not growing at the normal rate, or with bladder or kidney problems. In either case, you'll be referred to a consultant for further tests.
High blood pressure. This causes the blood vessels in your placenta to constrict, cutting down on the oxygen your baby receives. If this happens, the baby diverts the available oxygen to his most important organs - the heart and brain - causing them to grow faster than the rest of his body, which may remain small. Pre-eclampsia has a similar effect on the baby. A scan can detect if your baby is growing properly. If you have high blood pressure before pregnancy, your midwife will monitor you carefully throughout. If you develop high blood pressure, or other signs of pre-eclampsia, later on, she'll refer you to a consultant obstetrician.
Smoking. Smoking reduces the amount of oxygen reaching your baby. Women who smoke are three times more likely to have a low birth-weight baby - up to 7oz or 200g lighter than normal - with an increased risk of complications after birth, too. If you need help giving up, call the NHS Pregnancy Smoking Helpline on 0800 169 9169 for support and advice.
Does size matter when your baby's born?
Healthy full-term babies really do come in all shapes and sizes. But there are times when your baby's size can affect his health, particularly in the first few days of life.
‘If a baby's small when he is born, he's in danger of his blood sugar levels dropping rapidly because he's used up all his energy stores in the womb and doesn't have any fat
stores left to convert,' says midwife Lorna. ‘So it's really important that he's fed and wrapped up well soon after he's born. He'll also get colder more quickly as he hasn't got as much body fat as a larger baby.
‘A big baby's blood sugar levels can drop too - especially if he's born
to a diabetic mum, and has high insulin levels. We'd carefully watch his temperature and his feeding. If he gets cold, his blood sugar could drop.'
Read more... How early will my baby bump start to show?