Baby Measuring Big?
- Julia Kitching
- Sep 3, 2023
- 7 min read
Updated: Jun 5
Have you been told that you are having a big baby?
Unfortunately, women and families being told that they are having a "big baby" is becoming more and more common in the UK and this often leads to unnecessary fear, worry and anxiety. There is no reliable measure to determine whether a baby will be born bigger than "normal" and the only real way of being able to determine the weight of a baby is when it is born.
Growth Scans For Babies Measuring Big
Ultrasound scans or growth scans, are not very reliable when trying to work out the weight of a baby. A recent Cochrane review (March 2023) states that "the estimation of the baby's weight is difficult before birth and not very accurate." The NICE guidelines consider a large baby for gestational age as having an estimated fetal weight above the 90th centile or weighing over 4000g on an ultrasound. Women who are told that their baby is considered a large baby for gestational age, are often recommended early induction or a planned caesarean section, to stop the baby growing too big. The reason for this is because large babies increase the risk of shoulder dystocia (05.% in non-diabetic women), needing help delivering the baby (e.g. forceps, ventouse) or an increased risk of severe perineal tearing, which would require repair in theatre.
When a woman is told that she is or might be having a big baby, this naturally creates anxiety and worry. For many women they have already heard people telling them that vaginal birth is "like s**tting a watermelon." If they are also told that their baby is bigger than an average sized baby, they then start to worry about how painful their birth is going to be. What many pregnant women aren't told though, is that the human body is incredible and your body is desired to birth a baby. Your body is designed to birth the right sized baby for you and during labour, the body adapts, stretches and makes space for your baby to come out. What is an average sized baby anyway? We are all different and there is no "one size fits all".
Big Baby Means a Change of Birth Plan
Many women who are told that they are having a big baby also start to worry about how this information will affect their birth plan. Does this mean that they will be encouraged to have an induced labour to reduce their baby getting too big in the womb? Will it mean that they are at an increased risk of needing an instrumental birth or caesarean section? Does it mean that they can't have a home birth, waterbirth or freedom of movement during labour?
Read the case study below about Lydia's experience of being told that she was having a big baby, when she was pregnant with her first baby.
Predicted Big Baby Case Study: Does this mean a change of birth plan and the end of the dream waterbirth?
When Lydia reached 35 weeks of her pregnancy, she went for her antenatal midwife appointment. At the appointment, her midwife measured Lydia's bump, using a tape measure. The midwife told Lydia that her baby was starting to measure big and it was now measuring on the 91st percentile. The midwife asked Lydia if there was any family history of "big babies" and Lydia explained that her husband was a big baby, when he was born. The midwife said that it looked like history was repeating itself and that there was going to be another big baby in the family. Lydia asked the midwife what would this mean for the birth and the midwife said that she would arrange for Lydia to have a growth scan at the hospital in the next few days and if the scan was predicting a big baby too, she would probably need to be induced and her dreams of a natural waterbirth would be out of the question.
Lydia left her appointment feeling worried, anxious and upset. She had been considered low risk throughout her pregnancy, with no complications. She had been reading a lot about the benefits of waterbirths and this was something that she had her heart set on. This new information of having a big baby changed everything. She spent that evening researching the risks of big babies, the pros and cons of induction and the process of caesarean sections. Her anxiety started to increase more and more and all she could now focus on, was her baby's birth and how hard it was going to be.
Two days after Lydia's midwife appointment, she got a call from the hospital, to say that they'd received the referral for a growth scan. However, due to the high volume of women being booked in for scans at the moment, they wouldn't be able to see her for another 5 days. This made Lydia feel so frustrated and upset, because she was worrying so much about the outcome of the scan and just wanted to know if her dream waterbirth was definitely off the cards and what the next steps would be.
The night before the scan, Lydia found it hard to sleep. She was imagining all kinds of scenarios for her birth. The day of the scan finally arrived and it was good news! Lydia's baby wasn't measuring big after all. He was exactly where he should be and was measuring on the 56th percentile. Lydia's dream of a natural waterbirth was back on. A few weeks later, Lydia birthed a beautiful baby boy. Her baby arrived just 2 days before his estimated due date, at home, in the birth pool, weighing a perfect 8lbs 6oz.
Unfortunately Lydia's experience isn't unusual and so many of my clients are being told that their baby is measuring big when they attend their antenatal appointments. It's almost becoming standard practice now and in most cases, these women are not carrying big babies at all and all that it creates is unnecessary worry and anxiety for a few days or even weeks. I had one previous client who had wanted to have a physiological birth, but was told that she needed to be induced due to an ultrasound scan estimating a big baby. Due to fear and coercion from her maternity team, she agreed to the induction. This induction led to complications at birth, which then lead to an unplanned, emergency caesarean section and what my client describes as a "negative birth experience". When her baby was born, he was not considered "big" at all. He was a healthy 7lb 9oz, but induced at 38weeks +5. He could have quite happily stayed in the womb until he was ready to be born and his Mother's birth experience could have been very different.
It is also worth mentioning here that if you are told that your baby is measuring big, this does not necessarily mean that you will experience shoulder dystocia during birth or that you will need to change your birth plan. RCOG, (2013) say that "shoulder dystocia is rare and only occurs in about one in 150 (0.7%) vaginal births. Shoulder dystocia is more likely with large babies but nevertheless there is no difficulty delivering the shoulders in the majority of babies over 4.5 kg (10 lb). Half of all instances of shoulder dystocia occur in babies weighing less than 4 kg (about 9 lb)."
You do not need to be induced if you don't want to be and you can still have a home birth if this is something that you would like. "Wherever you give birth, your midwife is trained to deal with shoulder dystocia." (RCOG, 2013). You might come up against some resistance from your care provider if you do choose to give birth at home, in water or decline an induction, but it is your choice where and how you give birth. Making an informed decision is what is important here.
The Big Baby Trial
A recent trial carried out in the UK, called "the big baby trial" displayed interesting results. Dr Sara Wickham (2025) says "Analysis according to random assignment, including the 25% of pregnancies in the standard care group that were also delivered early, showed no statistically significant difference in incidence of shoulder dystocia between the two study groups.”
"We already know that many of the women who are told that their baby is big after having an ultrasound scan, and who are then told they need induction because of this do not actually have a big baby. Many studies show a margin of error of 15%, and up to 20%. This is why so many of the women who are told that their baby is big end up giving birth to an average-sized baby." (Dr Sara Wickham, 2025).
You can read the full "big baby trial" in the Lancet and see the outcome of Induction of labour versus standard care to prevent shoulder dystocia in foetuses suspected to be large for gestational age in the UK (the Big Baby trial).
Inductions & Caesarean Section Risks
Inductions and caesarean sections come with their own risks. If you have been told that your baby is measuring big, weigh up the pros and cons of delivering an estimated large baby and the risks associated with that, verses the risks of inductions and c-sections. Also bear in mind, that inducing a baby early (37-38 weeks) could increase the risk of baby needing treatment when they are born. E.g. evidence indicates that early induction can increase your babies risk of jaundice at birth, which would require treatment and potentially a longer stay in hospital. Ultrasound scans are not very reliable at estimating a baby's gestation either. It could be that a baby being induced at 37 weeks, could in fact only be 35 weeks gestation at birth. Again, this could create additional issues at birth, where baby might need to go into the NICU (Neonatal Intensive Care Unit) for help and treatment.
Always use the BRAINS acronym when faced with a difficult decision, to help you to make informed decisions, that are right for you and your baby.
B - Benefits
R - Risks
A - Alternatives
I - Intuition
N - Do nothing
S - Second opinion
Dr Sara Wickham has some excellent information on her website about induction and big babies. Another great resource regarding big babies in pregnancy, is Evidenced Based birth.
Making informed decisions during pregnancy is not always easy, especially when there is a lot of conflicting information. My hypnobirthing courses and my antenatal and birth doula support packages provide non bias, evidence based information and teach you all about making informed decisions during pregnancy and birth and about how to navigate the complicated maternity system. If you would like to know more, visit my website or get in touch.
Julia x
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